Power-Programmierung/CD1.mdf/rexl/rexlref.doc

Text File | 1992-08-16 | 240KB | 7,769 lines

                     RExL  Version 2.11


     A Rule-based Applications Development Environment

                            From

                    The Software Loft,
                    Kiemar House,
                    Shanakiel Road,
                    Cork City,
                    Ireland.

                    Tel: [+353] 21-302511
                    Fax: [+353] 21-343562

          Internet:      [e-mail]

          Compuserve:    100042,1237



              -- Part II -- The Appendices --




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                --|       |    |-------------------
                  |   ____|__  |  Association of
                  |  |       |_|  Shareware
                  |__|   o   |    Professionals
                -----|   |   |---------------------
                     |___|___|    MEMBER




This program is produced by  a member of the Association  of
Shareware Professionals (ASP). ASP  wants to make sure  that
the shareware principle works for you. If you are unable  to
resolve a shareware-related  problem with an  ASP member  by
contacting the member directly, ASP may be able to help. The
ASP Ombudsman can help you resolve a dispute or problem with
an ASP member,  but does not  provide technical support  for
members' products. Please write to the ASP Ombudsman at  545
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message via CompuServe Mail to ASP Ombudsman 70007,3536.

                             o

Information in this  document is subject  to change  without
notice and does  not represent a commitment  on the part  of
The Software Loft.   The software  described in this  manual
may be  used and  copied within  the  terms of  the  license
agreement.

Turbo C, Turbo Pascal and Sidekick are registered trademarks
of  Borland  International.    dBase  III+  and  dBase   are
registered trademarks of Ashton-Tate.

(C)  Copyright,  The  Software  Loft,  1992.    All   rights
reserved.  If you have  any difficulties, please contact  us
at the address above.


































                       Contents



     Chapter 1  Function Families                     3
        1.1  Introduction . . . . . . . . . . . . . . 3
        1.2  Array handling . . . . . . . . . . . . . 3
        1.3  Binary operations  . . . . . . . . . . . 4
        1.4  Database operations  . . . . . . . . . . 4
        1.5  Date and time manipulation . . . . . . . 5
        1.6  RExL error handling functions  . . . . . 6
        1.7  Keyboard handling functions  . . . . . . 7
        1.8  Operating system interface functions . . 7
        1.9  Financial functions  . . . . . . . . . . 8
        1.10  Mathematical functions  . . . . . . . . 8
        1.11  Screen handling functions . . . . . . . 9
        1.12  Miscellaneous functions . . . . . . . . 9

     Chapter 2  The Database Module                  11
        2.1  Introduction to Databases  . . . . . .  11
        2.2  Indexes  . . . . . . . . . . . . . . .  13
        2.3  Using Database Files . . . . . . . . .  15
           2.3.1  Opening and selecting files . . .  15
           2.3.2  Reading and writing to files  . .  16
              2.3.2.1  Using functions  . . . . . .  16
              2.3.2.2  Direct field access  . . . .  18
           2.3.3  Moving around in a file . . . . .  20
           2.3.4  Miscellaneous functions . . . . .  20
              2.3.4.1  Statistical analysis of
                       data . . . . . . . . . . . .  20
              2.3.4.2  Deletion of information  . .  20
              2.3.4.3  Other functions  . . . . . .  21

     Chapter 3  Function Reference                   23

     Chapter 4  Keystroke reference                  95
        4.1  Editor keystrokes  . . . . . . . . . .  95
        4.2  Screen designer keystrokes . . . . . .  97
        4.3  Debugger keystrokes  . . . . . . . . .  99





                             i



     Chapter 5  Error Messages                      101
        5.1  Error messages common to runtime and
             editor . . . . . . . . . . . . . . . . 101
           5.1.1  Bad help file format  . . . . . . 101
           5.1.2  Cannot locate system  . . . . . . 101
           5.1.3  Cannot open print file  . . . . . 101
           5.1.4  Couldn't open file  . . . . . . . 101
           5.1.5  Macros nested too deep (20=max) . 102
           5.1.6  Help file index is not loaded . . 102
           5.1.7  Unable to locate help file  . . . 102
           5.1.8  Macro recursion not allowed . . . 102
           5.1.9  Error loading configuration
                  file  . . . . . . . . . . . . . . 102
           5.1.10  Zero memory allocation
                   request! . . . . . . . . . . . . 102
           5.1.11  Not enough memory to perform
                   selected operation . . . . . . . 103
           5.1.12  This window is not movable . . . 103
           5.1.13  No directories available . . . . 103
           5.1.14  No files in directory  . . . . . 103
           5.1.15  No macros defined  . . . . . . . 103
           5.1.16  --- Out of memory ---  . . . . . 103
           5.1.17  No screens defined . . . . . . . 103
           5.1.18  Not enough memory to load
                   system . . . . . . . . . . . . . 103
           5.1.19  No unused rules available  . . . 104
           5.1.20  No unused screens available  . . 104
           5.1.21  No variables defined . . . . . . 104
           5.1.22  Rule is not used in current
                   listing  . . . . . . . . . . . . 104
           5.1.23  Error saving configuration
                   file . . . . . . . . . . . . . . 104
           5.1.24  Screen is not used in current
                   listing  . . . . . . . . . . . . 104
           5.1.25  Screen file is corrupt . . . . . 104
           5.1.26  Too many files open  . . . . . . 105
           5.1.27  Too many keys in macro
                   (500=max)  . . . . . . . . . . . 105
           5.1.28  Variable is not used in current
                   listing  . . . . . . . . . . . . 105
           5.1.29  Wrong source file format . . . . 105
           5.1.30  Wrong screen file format . . . . 105
           5.1.31  Error opening screen file  . . . 105
        5.2  Error messages unique to editor  . . . 106
           5.2.1  Incorrect format in listing
                  file  . . . . . . . . . . . . . . 106
           5.2.2  Cannot nest fields  . . . . . . . 106



                             ii



           5.2.3  Can only delete recursed rule from
                  first level of recursion  . . . . 106
           5.2.4  Unable to locate runtime module . 106
           5.2.5  Area crosses fields . . . . . . . 106
           5.2.6  Can't have a field of this type in
                  this screen . . . . . . . . . . . 107
           5.2.7  Illegal array dimension . . . . . 107
           5.2.8  Maximum number of fields
                  reached . . . . . . . . . . . . . 107
           5.2.9  Memory low, should save now!  . . 107
           5.2.10  Not used in listing  . . . . . . 107
           5.2.11  This is the main rule and is called
                   to start the kbs . . . . . . . . 107
           5.2.12  Cannot change rule name to one
                   already existing . . . . . . . . 107
           5.2.13  This screen already exists . . . 108
           5.2.14  Toggle fields must be more than 5
                   and less than 75 characters
                   wide . . . . . . . . . . . . . . 108
           5.2.15  Unable to create screen file . . 108
           5.2.16  Error saving file  . . . . . . . 108
           5.2.17  Error loading file . . . . . . . 108
           5.2.18  Error loading screen file  . . . 108
           5.2.19  Cannot change name of Main
                   Program  . . . . . . . . . . . . 108
        5.3  Error messages unique to runtime-
             debugger . . . . . . . . . . . . . . . 109
           5.3.1  Array bounds overflow . . . . . . 109
           5.3.2  Can't set a breakpoint here . . . 109
           5.3.3  Cannot open printer for output  . 109
           5.3.4  Cannot find editor  . . . . . . . 109
           5.3.5  Divide by zero  . . . . . . . . . 109
           5.3.6  String-numeric collision  . . . . 109
           5.3.7  Can't have string for radio button
                  parameter . . . . . . . . . . . . 110
           5.3.8  Stack underflow . . . . . . . . . 110
           5.3.9  Stack overflow  . . . . . . . . . 110
           5.3.10  Numeric value out of range . . . 110
           5.3.11  Rule stack overflow  . . . . . . 110
           5.3.12  Invalid database file handle . . 110
           5.3.13  Unable to allocate rule stack  . 111
           5.3.14  Math error : Parameter out of range
                   in function XXX  . . . . . . . . 111
           5.3.15  Math error : Parameter singularity
                   in function XXX  . . . . . . . . 111
           5.3.16  Math error : numeric overflow  . 111
           5.3.17  Math error : numeric underflow . 111
           5.3.18  Math error : precision loss  . . 111


                            iii



        5.4  Critical Errors  . . . . . . . . . . . 111
           5.4.1  Write protect error . . . . . . . 112
           5.4.2  Drive not ready . . . . . . . . . 112
           5.4.3  Printer out of paper  . . . . . . 112
           5.4.4  Write fault . . . . . . . . . . . 112
           5.4.5  Read fault  . . . . . . . . . . . 112
           5.4.6  General Failure . . . . . . . . . 112
           5.4.7  Sector not found  . . . . . . . . 113
           5.4.8  Unknown unit  . . . . . . . . . . 113
           5.4.9  Unknown command . . . . . . . . . 113
           5.4.10  CRC error  . . . . . . . . . . . 113
           5.4.11  Bad request structure length . . 113
           5.4.12  Seek error . . . . . . . . . . . 113
           5.4.13  Unknown media type . . . . . . . 113

     Chapter 6  Extra Utilities                     115
        6.1  RExLPC . . . . . . . . . . . . . . . . 115
        6.2  RDU  . . . . . . . . . . . . . . . . . 117
           6.2.1  Introduction  . . . . . . . . . . 117
           6.2.2  Loading and Running . . . . . . . 117
           6.2.3  RDU menu system . . . . . . . . . 117
              6.2.3.1  File Menu  . . . . . . . . . 117
           6.2.4  Edit Menu . . . . . . . . . . . . 119
           6.2.5  Search Menu . . . . . . . . . . . 121
           6.2.6  Utilities Menu  . . . . . . . . . 122
           6.2.7  Options Menu  . . . . . . . . . . 124
        6.3  RExLRD . . . . . . . . . . . . . . . . 125
        6.4  RExLRT . . . . . . . . . . . . . . . . 126
        6.5  ScrList  . . . . . . . . . . . . . . . 127
        6.6  ScrFix . . . . . . . . . . . . . . . . 128
        6.7  ScrGrab  . . . . . . . . . . . . . . . 129
        6.8  ScrXtrct . . . . . . . . . . . . . . . 130
        6.9  ScrAdd . . . . . . . . . . . . . . . . 131
        6.10  MI  . . . . . . . . . . . . . . . . . 131
        6.11  KbdSpeed  . . . . . . . . . . . . . . 134
        6.12  KbdScan . . . . . . . . . . . . . . . 134

     Chapter 7  Afterword                           137












                             iv









                        Tables


     Table 1.1: Functions in AR function family . . . 3
     Table 1.2: Functions in BT function family . . . 4
     Table 1.3: Functions in DB function family . . . 5
     Table 1.4: Functions in DT function family . . . 5
     Table 1.5: Functions in ER function family . . . 6
     Table 1.6: Functions in KB function family . . . 7
     Table 1.7: Functions in OS function family . . . 8
     Table 1.8: Financial functions . . . . . . . . . 8
     Table 1.9: Math functions  . . . . . . . . . . . 9
     Table 1.10: Screen functions . . . . . . . . . . 9
     Table 1.11: Miscellaneous functions  . . . . . .10
     Table 2.1: Simple Database Record Structure  . .12
     Table 2.2: dBase Expression Compatibility with
                RExL  . . . . . . . . . . . . . . . .14
     Table 2.3: Miscellaneous Database Functions  . .21
     Table 3.1: ARsize() Input Indexing . . . . . . .26
     Table 3.2: BEEP() Frequencies  . . . . . . . . .29
     Table 3.3: Color Attribute Codes . . . . . . . .30
     Table 3.4: DISPLAY() escape sequences  . . . . .51
     Table 3.5: Valid Format Specifiers for
                DTformat()  . . . . . . . . . . . . .54
     Table 3.6: OSdir() File Attribute Coding . . . .74
     Table 3.7: OSdriveok() return values . . . . . .76
     Table 3.8: OSstat() Return Indexing  . . . . . .78
     Table 3.9: CPU Type Return Coding  . . . . . . .79
     Table 3.10: Coprocessor Type Return Coding . . .79
     Table 3.11: Video Adapter Type Return Coding . .79
     Table 3.12: Color Attribute Codes  . . . . . . .81
     Table 4.1: Cursor movement keys  . . . . . . . .95
     Table 4.2: Hilite bar movement keys  . . . . . .95
     Table 4.3: Modifier keys . . . . . . . . . . . .96
     Table 4.4: Editor list keys  . . . . . . . . . .96
     Table 4.5: Editor miscellaneous keys . . . . . .96
     Table 4.6: Screen designer movement keys . . . .97
     Table 4.7: Screen designer field definition
                keys  . . . . . . . . . . . . . . . .97
     Table 4.8: Screen designer line draw keys  . . .97
     Table 4.9: Screen designer miscellaneous keys  .98
     Table 4.10: Screen designer block mark keys  . .98


                             v



     Table 4.11: Debugger hilite bar movement keys  .99
     Table 4.12: Debugger list keys . . . . . . . . .99
     Table 4.13: Debugger miscellaneous keys  . . . .99
     Table 4.14: KB function return values  . . . . 100
     Table 6.1: Keystrokes in structure create  . . 122













































                             vi
  - Appendices.                         Page: 3 -








                         Chapter 1

                     Function Families


1.1  Introduction


This appendix gives a brief  introduction to the use of  and
the design behind  the the seven  function families in  RExL
and the various miscellaneous functions.


1.2  Array handling


There are nine functions which are used to manipulate arrays
and determine information about them.  The functions are  as
follows:

         Table 1.1: Functions in AR function family

ARavg()        ARcount()      ARinit()
ARmax()        ARmin()        ARsize()
ARstd()        ARsum()        ARvar()

The functions fall into two groups, the smaller first  group
has two  functions  in  it:  ARinit()  and  ARsize().    The
ARinit() function is used to  initialise the contents of  an
array, while the second determines, at runtime, the size  of
a particular dimension of an array.

The other functions in this family are used for  statistical
analysis of the contents of the arrays.  The function  names
are based upon  similar functions  found in  Lotus 123,  and
where appropriate, the parameter lists are the same.








 - RExL  Version 2.11  Copyright 1992, The Software Loft -
  - Appendices.                         Page: 4 -


1.3  Binary operations


There are six functions, using the initial letters BT  which
are used to perform binary operations.  The functions are as
follows:

         Table 1.2: Functions in BT function family

BTand()        BTnot()        BTor()
BTshl()        BTshr()        BTxor()

The function  names  are  based  upon  the  equivalent  8086
assembly language functions.   All the BT functions  convert
their  parameters  to  sixteen  bit  words,  any  parameters
greater than 65535  being set  to 65535  and any  parameters
less than 1 being set to 0.

Typically, these functions are used in conjunction with  the
four memory access  functions, PEEK(),  PEEKW(), POKE()  and
POKEW() to determine  information which  cannot be  obtained
through the other system functions.

For example, to determine if the NumLock state is active  or
not, the following line could be used:

          [Expr] NumLockOn:=BTand(PEEK(0,1047),32)

The use of the memory access functions should be avoided  if
you intend  your  application  to run  on  widely  different
machines.


1.4  Database operations


The thirty-nine dBase file and index manipulation  functions
use the initial letters DB.  The functions are as follows:












 - RExL  Version 2.11  Copyright 1992, The Software Loft -
  - Appendices.                         Page: 5 -


         Table 1.3: Functions in DB function family

DBappend()     DBavg()        DBbottom()
DBcloseall()   DBclosedbf()   DBclosendx()
DBcount()      DBcountflds()  DBdelete()
DBdeleted()    DBexact()      DBgo()
DBlocate()     DBmax()        DBmin()
DBmkdbf()      DBmkndx()      DBnext()
DBpack()       DBprev()       DBrecall()
DBreccount()   DBrecno()      DBreindex()
DBreplace()    DBrnum()       DBrstr$()
DBseek()       DBseldbf()     DBselndx()
DBskip()       DBstd()        DBstruct()
DBsum()        DBtop()        DBusedbf()
DBusendx()     DBvar()        DBzap()

Because of the size and complexity of the database module in
RExL, it is treated on its own in the next appendix.


1.5  Date and time manipulation


The eighteen date  and time manipulation  functions use  the
initial letters DT.  The functions are as follows:

         Table 1.4: Functions in DT function family

DTdate()       DTdate$()      DTdatevalue()
DTday$()       DTdayno()      DTformat()
DThourno()     DTminuteno()   DTmonth$()
DTmonthno()    DTnow()        DTsecondno()
DTsetdate()    DTsettime()    DTtime()
DTtime$()      DTtimevalue()  DTyearno()

The date functions  are again, based  largely upon those  in
Lotus 123, with a few minor inconsistencies removed.

The date  module can  use dates  in  any of  the three  most
common date formats, European,  American and Japanese.   The
exact format which is in use initially is determined by  the
settings in the CONFIG.SYS file  in your machine.  If  there
is no  specific format  set up,  then the  date format  will
default to American.  The DTformat() command can be used  to
set the  date and  time formats  and separators  explicitly,
overriding the defaults.




 - RExL  Version 2.11  Copyright 1992, The Software Loft -
  - Appendices.                         Page: 6 -


Date and  time  information  are  stored  in  RExL  as  real
numbers.  The integer portion  of a date-time number is  the
Julian day number  while the  fractional part  is the  time,
expressed as a fraction of 24 hours.

The Julian day number of a particular date is the number  of
days elapsed since and including the first of January,  4713
BC (the  reasons for  this exact  date being  chosen as  the
origin are  historically amusing).   The  Julian day  number
system is used widely in date calculations and should not be
confused with the Julian Calendar.   The algorithms used  in
RExL to calculate the Julian day number do not take  account
of the ten  day transition from the  Julian Calendar to  the
Gregorian  Calendar  which  occurred  from  October  5th  to
October 15th  in 1582  in Rome  and at  various other  later
dates around the rest of the world.

Dates before 0 AD cannot be represented in RExL.  Apart from
any other  considerations, there  was no  standard  calendar
then, rendering calculations somewhat useless.

Date and time functions which  return a date or time  number
will return zero if the date or time was invalid.


1.6  RExL error handling functions


The five error  handling functions use  the initial  letters
ER. The functions are as follows:

         Table 1.5: Functions in ER function family

ERclear()      ERmsg$()       ERnum()
ERok()         ERwatch()

Whenever an error  occurs in  the runtime  portion of  RExL,
internal variables save the text of the error and the  error
number.  These  variables can be  interrogated by using  the
ERmsg$() function (to  retrieve the text  of the error)  and
ERnum() (to retrieve the error code).

If no  errors have  occurred, then  calls to  ERmsg$()  will
return an  empty string  and calls  to ERnum()  will  return
zero.  Once an error has occurred, the text and error number
remain fixed until the next error occurs, an application  is
LOAD()'ed or the ERclear() function is used.



 - RExL  Version 2.11  Copyright 1992, The Software Loft -
  - Appendices.                         Page: 7 -


While the  development of  an  application is  in  progress,
errors should be left on, to detect errors such as divide by
zero, which  would otherwise  not be  seen.   In  the  final
distribution version, the error display can be disabled with
the ERwatch() function.


1.7  Keyboard handling functions


The five keyboard handling functions use the initial letters
KB.  The functions are as follows:

         Table 1.6: Functions in KB function family

KBclear()      KBlast()
KBread()       KBready()
KBwait()

The IBM PC uses a keyboard buffer to store keystrokes  until
they can be processed by a program.  The normal size of  the
buffer is 15 keystrokes.  The KBclear() function resets  and
empties the  keyboard buffer,  while the  KBready()  reports
whether a keystroke is pending  in the keyboard buffer.  The
other two functions  in the  group are  used for  retrieving
keystrokes from the  buffer, optionally  waiting a  variable
time span for one.   When a screen has been terminated,  the
KBlast() function  can be  used to  determine the  keystroke
which caused its termination.

If a keystroke returned by RExL is a character key, then the
ASCII code of  the character will  be returned  immediately.
Keys that  do not  have ASCII  codes, such  as the  function
keys, return a more complex coding, the details of which are
not necessary. The complete  list of function return  values
is listed in appendix D, with the other keystrokes RExL  can
return.   Note that  the <Insert>  key  is captured  by  the
runtime module and is not returned to the application.


1.8  Operating system interface functions


The thirteen operating system interface functions, which use
the initial letter code OS, are as follows:





 - RExL  Version 2.11  Copyright 1992, The Software Loft -
  - Appendices.                         Page: 8 -


         Table 1.7: Functions in OS function family

OScd()         OScmd()   OScopy()
OSdel()        OSdir()   OSdrive()
OSexists()     OSmd()    OSnumber()
OSrd()         OSren()   OSstat()
OSwd$()

These functions  perform  most  of the  operations  commonly
needed to interface  with the operating  system under  which
RExL is  working.    The commands  are  modelled  after  the
corresponding DOS commands and require the same parameters.

The OSstat()  function is  the only  function in  the  group
which has no direct DOS counterpart.  It returns the  status
of the machine,  including the  processor, co-processor  and
display adapter type as well as the operating system version
and information about the currently selected disk.


1.9  Financial functions


The financial functions in RExL are used in the  calculation
of ordinary annuities.   There are  seven functions in  this
group which does not use a common initial two-letter group.

               Table 1.8: Financial functions

CTERM()        FV()
PMT()          PV()
RATE()         SLN()
SYD()          TERM()

The functions in  this group are based  upon those in  Lotus
123.  The annuity due for the FV() and PV() functions may be
calculated easily by multiplying the result of the  ordinary
annuity by the expression 1+rate, where rate is the periodic
interest rate.


1.10  Mathematical functions


As with the financial functions,  the math functions do  not
have a  common  initial  letter pair.  The  thirty-one  math
functions are as follows:



 - RExL  Version 2.11  Copyright 1992, The Software Loft -
  - Appendices.                         Page: 9 -


                 Table 1.9: Math functions

ABS()     ACOS()    AND()
ASIN()    ATAN()    CEIL()
COS()     DEG()     DIV()
EQV()     EXP()     FALSE()
FLOOR()   IMP()     LOG()
LOG10()   MAX()     MIN()
MOD()     NOT()     OR()
PI()      POW()     RAD()
RAND()    ROUND()   SEED()
SIN()     SQRT()    TAN()
TRUE()    XOR()

All math functions  requiring an angle  parameter must  have
the angle expressed in radian measure.  The RAD() and  DEG()
functions can be used to convert degrees to radians and vice
versa.


1.11  Screen handling functions


The functions in this section are used for handling screens:
input, output, box drawing and painting areas as well as for
loading screens.  There are fifteen functions in this group:

                Table 1.10: Screen functions

BEEP()         CODE()         ATTRXY()
BOX()          CHAR$()        CHARXY$()
CLS()          DISPLAY()      FILL()
GOTOXY()       INPUT()        INPUT$()
INVERSE()      LOADSCR()      PAINT()


1.12  Miscellaneous functions


This final group of functions  fall into no clearly  defined
grouping.  The functions in the group are as follows:









 - RExL  Version 2.11  Copyright 1992, The Software Loft -
  - Appendices.                         Page: 10 -


            Table 1.11: Miscellaneous functions

ESCWATCH()     EXACT()        FIND()
IIF()          IF$()          INIT()
LEFT$()        LENGTH()       LOAD()
LOWER$()       MID$()         OUTPUT()
PAUSE()        PEEK()         PEEKW()
POKE()         POKEW()        QUIT()
REPEAT$()      REPLACE$()     RIGHT$()
SOUNDEX$()     STRING$()      SUFFIX$()
TRIM$()        UPPER$()       VALUE()
VERSION()






































 - RExL  Version 2.11  Copyright 1992, The Software Loft -
  - Appendices.                         Page: 11 -








                         Chapter 2

                    The Database Module


The database function family, the largest single grouping of
functions, in RExL is fully compatible with the database and
index file format used in dBase III+.  Since this feature is
central to RExL,  it's treated on its  own in this  appendix
which contains  a  complete  introduction  to  the  database
facilities in RExL.


2.1  Introduction to Databases


There are a few terms relating to databases which need to be
understood before we can move on to the next section.

Most database formats, including the dBase format used here,
store their information in fixed fields.  A field is  simply
storage area of fixed length (known as the field size) which
is referenced from  RExL through a  field name.   The  field
names follow the  same conventions as  RExL variable  names,
save that the  dollar character `$'  is not  used to  denote
strings. The maximum width of a field name in the dBase file
format is ten characters.

Each field can be one of the following four different types:

    o  Numeric: which are used to store numeric  information
       within a fixed number of  digits.  The maximum  field
       width of  a numeric  field is  nineteen digits.    If
       there are decimal  fractions to be  stored, then  the
       field must contain space for a decimal point and  the
       field must also have a fixed decimal fraction  width,
       at most two less than the size of the field.

    o  String: These fields are  used to store character  or
       string information with a maximum field width of  255
       characters.   Because of  the limit  of 80  character
       long strings  in the  current  release of  RExL,  any


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       fields  which  are  wider  then  80  characters   are
       truncated.

    o  Date: This field,  used to store  dates, has a  fixed
       field width  of  8  characters.  Since  there  is  no
       intrinsic  date  type  in   RExL,  date  fields   are
       converted to Julian day numbers, compatible with  the
       date system in use elsewhere in RExL.

    o  Logical: This  final field  type stores  yes-no  type
       logical information.  As with the date fields,  there
       is no intrinsic logical data type in RExL, so logical
       information is  returned as  a  numeric type,  0  for
       False and 1 for True.

Traditionally, to avoid having to repeat the field types too
often, the types are abbreviated  to single letter: `N'  for
numeric, `C'  for  character,  `D'  for  date  and  `L'  for
logical.  The memo type, which is not commonly used in dBase
applications, is not supported in RExL.

Fields  are   collected   together   to  form   records   of
information.

Whenever an application  has a database  open for use,  RExL
maintains a pointer, known as  the record pointer, into  the
database pointing  at the  record which  all operations  are
based upon.   When a database  is first  opened, the  record
pointer is placed at the first record in the database.

As a  complete example  of a  record structure,  a  customer
database might be designed as follows:

        Table 2.1: Simple Database Record Structure

Field Name     Type      Width          Decimal Places
CUSTNAME       `C'       30
BALANCE        `N'       8                   2
MAILSHOT       `L'       1
NEXTBILL       `D'       8

The above  database structure  demonstrates the  use of  the
four different field types.  When databases are created, the
width of the  logical and date  fields is set  automatically
and does not have to be specified, the same is true for  the
decimal places specifier in character field types.




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Databases are  stored  on  disk with  a  file  extension  of
".DBF",  so  the   above  structure  could   be  stored   as
"CUSTOMER.DBF".


2.2  Indexes


Databases are  designed for  the  storage and  retrieval  of
large amounts of information.  If the information is held in
an random  manner  (like  a shuffled  pack  of  cards)  then
searching for a  particular item of  information can  become
prohibitively slow if there are large numbers of records  in
the database. The dBase file format specifies a way in which
indexes may be  generated through  which it  is possible  to
access information rapidly in a large database.

An index file, used to store the indexing information, is  a
separate DOS file (using the extension ".NDX") which is used
in tandem  with a  database file  to allow  rapid access  to
specific information.   This  rapid  access is  achieved  by
storing the indexing information in strict order (alphabetic
or date or numeric).

The function of the index file is analogous to a card  index
system in a library, where  a box contains a sorted list  of
cards, one  for each  book in  the library.   When  somebody
looks for a  book, the card  index can  be searched  quickly
(since it is sorted) and upon finding the wanted book  name,
the card will contain some information on how to locate  the
book in  the  library.  In  the same  way,  the  index  file
contains sorted information  together with  pointers to  the
records in the database which  match the information in  the
index file.

The index  is  generated  using an  index  expression  which
defines the order in which  the records in the database  are
to be  retrieved in.   Initially,  when the  index is  first
created, the index expression  is evaluated for all  records
in  the  database.    Subsequently,  whenever  a  record  is
modified, added or removed from  the database, the index  is
updated to reflect the new contents of the database.

In the example from the end of the previous section, if  the
developer decided that  the records were  to be sorted  with
respect to the name of the customer, then an index could  be
generated with the  index expression CUSTNAME.   Thus,  when
the user  of the  end system  wanted  to view  a  particular


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customer's record, the customer  name would be entered,  the
name would then  be searched for  in the  index file and  if
located, would then be returned to the user of the system.

Since the index  files used by  RExL may  also be used  with
dBase, Clipper and other packages which adhere to the ".NDX"
standard, the search expression  must be a dBase  expression
and not a  RExL expression. The  simplest dBase  expressions
are simply  field  names  and for  most  purposes,  this  is
sufficient.  The  RExL call  to generate  the customer  name
index from the previous paragraph would be as follows:

            [Expr] DBmkndx("CUSTndx","CUSTNAME")

This  would  create  an  index  file  called  "CUSTndx.NDX",
sorting  the  records  with  respect  to  the  field   named
"CUSTNAME".

The dBase expression parser built into RExL also copes  with
more complicated expressions involving dBase function  calls
and mathematical  operators.   The following  table gives  a
brief summary  of  the  functions and  operators  supported:
(dBase  does  not   follow  the   dollar  character   string
convention, so some of the  functions in the table may  seem
slightly at odds with the rest of RExL.)

    Table 2.2: dBase Expression Compatibility with RExL

Function       Meaning
* + - / ^      Ordinary mathematical operators
>= <= >
< = <>         Ordinary relational operators
DATE()         Return system date as `D'
DELETED()      Return delete of current record as `L'
DTOC()         Convert date field to `C'. (not recommended)
DTOS()         Convert date field to `C'. (recommended)
CTOD()         Convert string to date.
IIF()          Equivalent to RExL IIF()
RECNO()        Returns the current record number
RECCOUNT()     Returns the number of records in the database
STR()          Convert number to string as STRING$()
SUBSTR()       Equivalent to RExL MID$()
TIME()         Return system time
VAL()          Convert string to number
UPPER()        Equivalent to UPPER$()
SOUNDEX()      Equivalent to SOUNDEX$()




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The  DTOC()  function  is  supported,  although  is  is  not
recommended as  an  index  expression function:    Since  it
returns the  year  as a  two  digits  instead of  four,  the
function can only cope with  dates in a single century.  The
DTOS() function returns the date as a string with the format
"yyyymmdd" (y for year,  m for month and  d for day) and  is
therefore more suitable for indexing since it can deal  with
multiple centuries.

A full description of the database functions above is beyond
the scope of this introduction.   Consult your dBase  manual
for precise  details on  how these  functions and  operators
operate.


2.3  Using Database Files


2.3.1  Opening and selecting files

The handling of database files  is based largely around  the
concept of  file  handles, which  are  very similar  to  the
notion of work-spaces used in the dBase documentation.  When
a data file is opened (using DBusedbf()) or an index file is
opened (using DBusendx()), a file handle (a reference number
greater than zero)  is returned to  RExL, through which  the
application can make references to that file or index.   The
advantage of the file handle system is that a  theoretically
arbitrary number of  files and indexes may  be kept open  at
any one time and any file or index can be referenced through
its file handle.   In practice  however, the  number of  DOS
files which may be opened simultaneously is limited (by DOS)
to twenty,  five of  which cannot  be reassigned,  so up  to
fifteen database and index files may be open simultaneously.
(Note that beginning  with version 2.10,  it is possible  to
access  multiple  database  files  without  having  to  make
repeated calls to DBseldbf().)

speech For  example, assuming  that  the database  file  and
index file from the previous sections have been created  and
exist in the work directory.  The following code can be used
to open and select the two files:

[Expr] DBFhandle:=DBusedbf("customer")
[Expr] NDXhandle:=DBusendx("custndx")
[Expr] DBseldbf(DBFhandle)
[Expr] DBselndx(NDXhandle)
[Expr] DBtop()


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The first line opens the  customer database and returns  the
database file handle  which RExL has  assigned to  it.   The
second line opens the index file and assigns the index  file
handle  to  NDXhandle.    Next,  the  database  file  opened
previously is selected  or made  the current  work file,  at
this point the records are  not yet sorted, since the  index
file has not been selected. The fourth line applies the sort
order to the current database.  Finally, the current  record
number is set to the first record in the database (it's good
practice always to know what the current record is).

In a real-life application,  the return values of  DBFhandle
and NDXhandle would  be checked for  validity, to make  sure
that they had been opened correctly.

2.3.2  Reading and writing to files

There are two  ways in which information  can be written  to
and read  from  database  files.    The  first  method  uses
specific functions to read and  write database files and  is
compatible with RExL version 2.00, but is cumbersome to use.
The second, newer and more efficient method is to use the  @
notation introduced  in  version  2.10, generally  known  as
`direct field access'.  The  next two subsections deal  with
both methods.

2.3.2.1  Using functions

There are four  functions which are used  to read and  write
the currently selected database file.  These are DBappend(),
used to  append a  blank  record to  the  end of  the  file,
DBreplace() to write to the file and DBrnum() and  DBrstr$()
to read from it.

a) Writing to a file

The DBreplace() command requires  two parameters, the  first
is the field name while  the second parameter, which may  be
either string or  numeric in  type, specifies  the value  to
place into the  field.  This function  is equivalent to  the
dBase  command  REPLACE.    The  action  of  DBreplace()  is
slightly more complicated than it may at first seem.   First
of all, if the field is numeric and the number being written
is too wide  for the field,  then the field  will be set  to
zero.  If the field  is string and the string being  written
is too long, then it will be truncated.




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It is also possible to write string values to numeric fields
(although the strings must clearly contain numeric value for
this to work) and to write numeric values to string  fields,
where \rexl\  will  attempt to  convert  the number  into  a
string before writing  it to  the field.   Generally,  these
cross-breed replacements should be avoided where possible.

For logical fields, a value of \true\ will be written to the
field if the second parameter is numeric and non zero, or if
it is string and equal to  "Y" "y" "T" or "t". In all  other
cases, the value written will be  false.  If the field is  a
date field,  then the  second parameter  will be  internally
converted to a date number and written to the field.

The DBappend()  command is  used to  place a  new and  blank
record at the end of  the currently selected database  file.
If this  has been  performed successfully,  then the  record
pointer will be placed there.

b) Reading from a file

The two functions DBrnum() and DBrstr$() are used to extract
information from the current  record.  DBrnum() returns  the
field expressed as a number, where possible, while DBrstr$()
returns the field  expressed as  a string,  which is  always
possible.

DBrstr$() is subject to much the same caveats as DBreplace()
as regards reading strings: If  the field contains a  string
longer than 80  characters, then it will  be truncated.   As
with DBreplace()  it is  possible, but  not recommended,  to
perform cross-breed reading, from  numeric fields to  string
variables and string fields to numeric values.

When the two  field reading  functions are  applied to  date
fields, the  return value  will be  the value  of the  field
converted to the appropriate  type.  Thus DBrstr$()  applied
to a date  field will return  a date  string in the  current
date format, while  a call to DBrnum()  applied to the  same
field  will  return  the  Julian  day  number  of  the  date
specified in the field.

The two functions  can also  be applied  to logical  fields,
where DBrnum() will return 1.0 for a true value in the field
and 0.0 for a false value. DBrstr$ will return "Y" for  true
and "N" for false.




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2.3.2.2  Direct field access

a) Basics

The `@' operator is used to access database fields  directly
and is mapped  internally to a call  to either DBrstr$()  or
DBrnum().  There  are two forms of  the operator, the  first
which corresponds  to DBrstr$(),  is `@$'  and is  used  for
accessing the value  of a field  as a  string.  The  second,
taking the place of the DBrnum() function, is the `@' symbol
on its own and is used to access  the value of a field as  a
string.

To use the access operator, it is simply placed at the start
of the database  field name. For  example, to  read a  field
called `CUSTNO', and  assign its  value to  a variable,  the
following expression could be written:

          [Expr] customer:=@custno

Similarly, the contents of a character field may be returned
to a string as follows:

          [Expr] name$:=@$name

where `NAME' is a character field.

As with  the read  functions  DBrstr$() and  DBrnum(),  full
cross-type read operations  are permitted.   This again,  is
most noticeable  when  using  date fields:    using  the  @$
operator on a  date field will  return a  date string  while
using the @  operator will return the  Julian Day Number  of
the date specified in the field.

Information may  also be  written to  the database  file  in
exactly the same manner as it is read, so that a string  may
be assigned to a string field using:

          [Expr] @$name:="Joe Smith"

and to a numeric field using:

          [Expr] @age:=24


b) Accessing multiple database files




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The syntax of  the @  operator can  be extended  to allow  a
single   token   to    access   multiple   database    files
simultaneously.   The  general  format  of  the  extended  @
operator is:

          Numeric value:      @<num_variable>.<field>
and
          String value:       @$<num_variable>.<field>

where <num_variable>  is a  simple (ie.  non-array)  numeric
variable whose value is the file handle for a database file,
the dot is a full stop character and <field> is the name  of
the field whose value is being assigned or retrieved.

If, for  example,  two database  files  had been  opened  as
follows:

          db_one:=dbusedbf("customer")
          db_two:=dbusedbf("orders")

then a character  field, NAME, in the  customer file can  be
accessed using the expression:

          @$db_one.name

while a numeric field `ORDERVAL'  in the orders file can  be
accessed using:

          @db_two.orderval

Note again  that only  simple numeric  variables can  appear
between the  @symbol  and the  full  stop.   Direct  numeric
values, expressions and arrays are not allowed.

This extension to  the format of  the @  operator is a  very
powerful feature and extends  considerably the power of  the
language in interrogating database files.  In particular, it
does away with  the need  to select  and reselect  different
database files in  order to use  them and  also reduces  the
likelihood of introducing bugs by having the wrong  database
open at a particular time.

Perhaps its  greatest benefit  is that  it allows  a  single
screen to access  multiple database  files, something  which
was extremely cumbersome in the previous version.





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2.3.3  Moving around in a file

There are  six functions  used to  move the  record  pointer
within the file  from one record  to another.   With all  of
these functions, the movement is carried out with respect to
the current index file, if one is open.

The first two  functions, DBtop() and  DBbottom(), move  the
record pointer to  the first and  last records  in the  file
while DBprev()  and  DBnext()  move the  previous  and  next
records.

DBskip() will skip, forward or backward through the file  by
a specified number of  records.  If an  index is open,  then
index ordering will  be used.  DBgo() is  used to  go to  an
absolute record  number, but  unlike DBskip(),  it does  not
obey any index.

There are two functions used to find information in a  file.
The first of these, DBlocate() is used to locate a  specific
string or  number  in a  database  field (date  and  logical
fields are  not currently  supported by  DBlocate()).   This
function is based upon the LOCATE command in dBase.

In a large file, locating a record may take some time, since
it must read  and check every  record to  see if the  search
condition is  met.    It  is  therefore  usually  better  to
generate an index and use  it with the DBseek() function  to
find information.  DBseek(), based upon the SEEK command  in
dBase, is used  to find information  in a  file through  its
current index.   Because the index  file is  kept in  strict
order, the seek can be performed very rapidly.

2.3.4  Miscellaneous functions

2.3.4.1  Statistical analysis of data

There  are  seven  functions,  based  largely  upon  similar
functions in Lotus 123, which  can be used to perform  basic
statistical analysis upon the data in a database file.   The
functions, covered fully in  the function reference, are  as
follows:  DBavg(),  DBcount(),  DBstd(),  DBsum(),  DBvar(),
DBmax() and DBmin().

2.3.4.2  Deletion of information

Four  functions  are   used  to  control   the  removal   of
information  from  database  files.  These  are  DBdelete(),


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DBdeleted(),  DBpack()  and  DBrecall().  When  a  call   to
DBdelete() is made to delete a record, the record is  marked
for deletion  and  not  physically removed  from  the  file.
Thus, a further call to DBrecall() can be made to unmark the
record to return it to its normal status.

The DBdeleted() function can be used to determine whether  a
record has  been  marked  for deletion  or  not,  while  the
DBpack() function will permanently  remove all records  from
the database which have been marked for deletion.

2.3.4.3  Other functions

There are nine  other functions  in the  database packed  in
RExL which are used to  perform maintenance on the  database
file itself.  These functions are

        Table 2.3: Miscellaneous Database Functions

Function       Use
DBcountflds()  Returns the number of fields in the database
DBexact()      Turn database case sensitivity on and off
DBmkdbf()      Create a database
DBmkndx()      Create an index file
DBreindex()    Re-create an index file
DBreccount()   Return the number of records in a database
DBrecno()      Return the current record number
DBstruct()     Return the current database structure
DBzap()        Remove all records from a database

By default, the database module is case sensitive,  contrary
to the rest of RExL.   This is for reasons of  compatibility
with dBase  which  is  case  sensitive.    However,  if  the
database files  will  not  be used  with  dBase,  then  case
sensitivity can  be  safely set  to  off.   If  index  files
generated with  case sensitivity  off are  used with  dBase,
then the  results are  unpredictable, since  the index  file
format is not identical.












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                         Chapter 3

                     Function Reference


--------------------------------------------------------------------

ABS(number)

ABS()  returns  the  absolute  value  (or  modulus)  of  the
parameter.

Returns:  The parameter expressed as a positive number

See also: FLOOR CEIL ROUND

Example:  val:=ABS(-10) Returns 10 to the variable val

Example:  val:=ABS(10) Returns 10 to the variable val

--------------------------------------------------------------------

ACOS(number)

Returns the arc-cosine of the parameter. The return value is
expressed in radians. To convert radians to degrees, use the
DEG() function. The value returned  will be in the range  of
zero radians to pi radians.

Returns:  A number

See also: ASIN ATAN DEG

Example:  val:=ACOS(0.5) Returns 1.04719775 radians to val.

--------------------------------------------------------------------
AND(log1,log2)

AND() performs a logical AND operation upon the two  logical
parameters passed to the function and returns the result  of
the  test.  The  function  returns  True  if  both   logical
parameters are True otherwise it returns False.


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Returns:  A number

See also: NOT EQV XOR OR IMP

Example:  val:=AND(TRUE(),FALSE())

          Returns False to to the variable val.

---------------------------------------------------------------------
ARavg(num[#],start,end)

ARavg() returns  the  average of  the  elements of  the  one
dimensional numeric  array parameter  between the  specified
start and end elements. Note that unlike ARcount(),  ARavg()
takes account of zero values in its calculation.

In order  to  determine if  the  value  for the  average  is
meaningful, you should also calculate the standard deviation
of the data, using the ARstd() function.

Returns:  A number

See also: ARcount ARsum DBavg

Example:  avg:=ARavg(score[#],0,9)

          Returns, to  the  variable  avg,  the  average  of
score[#] over the first to tenth elements inclusive.

---------------------------------------------------------------------
ARcount(numstr[#],start,end)

ARcount() counts the elements  of the one dimensional  array
parameter which are  nonzero, if  the array  is numeric,  or
nonempty, if  the array  is of  type  string. The  count  is
performed between  the  specified  start  and  end  elements
inclusive.

Returns:  The number of nonempty elements

See also: ARavg ARsum DBcount

Example:  n:=ARcount(name$[#],0,2)

          Returns, to the variable n, the number of nonempty
strings in the string array, name$[#], between the first and
third elements.



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---------------------------------------------------------------------
ARinit(numstr[#])

ARinit() clears all  elements of an  array, setting  numeric
array values  to  0  and  string array  values  to  "".  The
function accepts arrays of any dimension.

Returns:  True

Example:  ARinit(name$[#])

          Resets all elements of name$[#] to "".

---------------------------------------------------------------------

ARmax(num[#],start,end)

ARmax() returns  the  maximum  value of  the  numeric  array
parameter between the specified start and end elements.

Returns:  A number

See also: ARcount ARmin

Example:  mmax:=ARmax(score[#],0,9)

          Returns, to the variable  mmax, the maximum  value
of the  numeric  array  score[#] over  the  first  to  tenth
elements inclusive.

---------------------------------------------------------------------

ARmin(num[#],start,end)

ARmin() returns  the  minimum  value of  the  numeric  array
parameter between the specified start and end elements.

Returns:  A number

See also: ARcount ARmax

Example:  mmin:=ARmin(score[#],0,9)

          Returns, to the variable  mmin, the minimum  value
of the  numeric  array  score[#] over  the  first  to  tenth
elements inclusive.

---------------------------------------------------------------------


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ARsize(numstr[#],dimension)

ARsize() returns the  size of  the specified  array, in  the
specified dimension. The dimensions are defined as follows:

             Table 3.1: ARsize() Input Indexing

Dimension           Meaning
     1              x dimension (first dimension)
     2              y dimension (second dimension)
     3              z dimension (third dimension)

Returns:  The size of the specified dimension

Example:  ARsize(name$[#],1)

          Returns the size of the first, or x, dimension  of
the string array name$[#].

---------------------------------------------------------------------

ARstd(num[#],start,end)

ARstd() returns  the population  standard deviation  of  the
values  in  num[#]  between  the  specified  start  and  end
elements,  inclusive.  This  function  uses  the  n   method
(biased)  to  determine  the   standard  deviation  of   the
population data.

The standard deviation can be thought of as a measure of the
validity of the average of the set of data. If the deviation
is small,  then the  average is  good, if  the deviation  is
large, then the value for the average could be meaningless.

Returns:  A number

See also: ARvar ARavg ARcount

Example:  std:=ARstd(score[#],0,9)

          Returns,  to  the   variable  std,  the   standard
deviation of the value of  score[#] over the first to  tenth
elements inclusive.

---------------------------------------------------------------------

ARsum(num[#],start,end)



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ARsum() returns the summation of the elements in the  num[#]
array  between  the  specified   start  and  end   elements,
inclusive.

Returns:  A number

See also: ARvar ARstd ARavg ARcount

Example:  sum:=ARsum(score[#],0,9)

          Returns, to the variable sum, the sum of the first
ten elements of the array score[#]

---------------------------------------------------------------------

ARvar(num[#],start,end)

ARvar() returns  the population  variance of  the values  in
num[#]  between  the  specified  start  and  end   elements,
inclusive. This  function  uses  the n  method  (biased)  to
determine the standard deviation of the population data.

ARvar() is  also  equal  to the  sqaure  of  the  population
standard deviation of the array, as returned by the  ARstd()
function.

Returns:  A number

See also: ARstd ARavg ARcount

Example:  var:=ARvar(score[#],0,9)

          Returns, to  the    variable var,  the  population
variance of the value of  the array score[#] over the  first
to tenth elements inclusive.

---------------------------------------------------------------------

ASIN(number)

Returns the inverse sine of the parameter. The return  value
is expressed in radians and  can range in value from from  -
pi/2 to pi/2.

Returns:  A number

See also: ACOS, ATAN



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Example:  val:=ASIN(0.5)

          Returns 0.52335987756 radians to val

---------------------------------------------------------------------

ATAN(number)

Returns the  inverse tangent  of the  parameter. The  return
value is expressed  in radians and can  range from -pi/2  to
pi/2.

Returns:  A number

See also: ASIN, ACOS

Example:  val:=ATAN(0.5)

          Returns 0.463647609 radians to val

---------------------------------------------------------------------

ATTRXY(xpos, ypos)

This function returns the attribute (or color value) of  the
character displayed at position (xpos,ypos).  The entry  for
BOX() has a table of color values which can be used to  work
out the actual colors used on the screen.

Returns:  A number between 0 and 255

See also: PAINT CHARXY

Example:  col:=ATTRXY(10,10)

          Returns the attribute  value of  the character  at
screen co-ordinates (10,10).

---------------------------------------------------------------------
BEEP(frequency,time)

Sounds the  computer's internal  speaker. The  frequency  is
measured in  Hertz  and  time  is  measured  in  millseconds
(thousandths of a second). If the time parameter is set to 0
then the  sound  will be  generated  until another  call  to
BEEP() is made.  If time  set to -1, the beeper is  switched
off. The following  is a  table of  natural frequencies  and
their corresponding musical notes.   time can be as long  as


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65534 milliseconds, or  about 65  seconds.   A frequence  of
440Hz is A below Middle C.

               Table 3.2: BEEP() Frequencies

  Note   Frequency Note   Frequency
     C    130.810   C    523.250
     D    146.830   D    587.330
     E    164.810   E    659.260
     F    174.610   F    698.460
     G    196.000   G    783.990
     A    220.000   A    880.000
     B    246.940   B    987.770
     C    261.630   C    1046.500
     D    293.660   D    1174.700
     E    329.630   E    1318.500
     F    349.230   F    1396.900
     G    392.000   G    1568.000
     A    440.000   A    1760.000
     B    493.880   B    1975.500

Returns:  True

Example:  BEEP(523.250,1000)

          Sounds the beeper at middle C for one second.

---------------------------------------------------------------------

BOX(x, y, w, h, color, type)

Draws a character box on screen. The parameters specify  the
coordinates of the top left corner and the desired width and
height of the box. The sixth parameter specifies the type of
box: type is zero for a single line box and one for a double
line box. The color  parameter specifies the attribute  with
which the box is to be  drawn. The interior of the box  will
be filled with spaces.  Attributes are calculated by  adding
the color number of the background (paper color) to that  of
the foreground  (ink) color.  The  following are  the  color
numbers:









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              Table 3.3: Color Attribute Codes

Color     Foreground     Background
Black          0              0
Blue           1              16
Green          2              32
Cyan           3              48
Red            4              64
Magenta        5              80
Brown          6              96
Light Gray     7              112
Dark Gray      8              (128)
Light Blue     9              (144)
Light Green    10             (160)
Light Cyan     11             (176)
Light Red      12             (192)
Light Mgnta    13             (208)
Yellow         14             (224)
White          15             (240)
Blink          128            -

If the  last  screen  displayed  during  execution  had  the
flash-intensity bit set to `intensity', then a further eight
background colors, indicated above by the bracketed numbers,
are available, at  the expense  of blinking.  Note that  the
background colors are derived from the foreground colors  by
multiplying by sixteen.

Returns:  True

See also: PAINT INVERSE

Example:  BOX(0,0,79,24,31,1)

          Draws a double lined white on blue box around  the
screen.

---------------------------------------------------------------------

BTand(bit1,bit2)

BTand() performs  a  bitwise  and  operation  upon  the  two
parameters. As with all the bit manipulation functions,  the
values are  internally converted  to sixteen  bit words,  so
numbers greated than 65535 are treated as 65535 and  numbers
less than 1 are treated as zero.

Returns:  A number between 0 and 65535


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See also: BTnot BTor BTshl BTshr BTxor

Example:  bt:=BTand(6,4)

          Returns a value of 4 to the variable bt

---------------------------------------------------------------------

BTnot(bits)

BTnot() performs  a  bitwise 16  bit  NOT operation  on  its
numeric parameter.

Returns:  A number between 0 and 65535

See also: BTand BTor BTshl BTshr BTxor

Example:  bt:=BTnot(65535) Returns  a  value  of  1  to  the
variable bt

---------------------------------------------------------------------

BTor(bit1,bit2)

BTor() performs a bitwise or operation upon two  sixteen-bit
parameters.

Returns:  A number between 0 and 65535

See also: BTnot BTand BTshl BTshr BTxor

Example:  bt:=BTor(6,4)

          Returns a value of 6 to the variable bt

---------------------------------------------------------------------

BTshl(bit1,bit2)

BTshl() performs a bitwise left shift of the first parameter
by the number of bits specified by the second parameter. The
return value of BTshl() is equivalent to the product of  the
first parameter and  two raised to the  power of the  second
parameter.

Returns:  A number between 0 and 65535

See also: BTnot BTor BTand BTshr BTxor


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Example:  bt:=BTshl(2,2)

          Returns a value of 8 to the variable bt

---------------------------------------------------------------------

BTshr(bit1,bit2)

BTshr()  performs  a  bitwise  right  shift  of  the   first
paremeter by  the number  of bits  specified by  the  second
parameter. The return value of BTshr() is equivalent to  the
quotient of the first parameter divided by two raised to the
power of the second parameter.

Returns:  A number between 0 and 65535

See also: BTnot BTor BTshl BTand BTxor

Example:  bt:=BTshr(8,2)

          Returns a value of 2 to the variable bt

---------------------------------------------------------------------

BTxor(bit1,bit2)

BTxor() performs a bitwise  exclusive or operation upon  the
two sixteen bit parameters.

Returns:  A number between 0 and 65535

See also: BTnot BTor BTshl BTshr BTand

Example:  bt:=BTxor(32767,16)

          Returns a value of 32751 to the variable bt

---------------------------------------------------------------------

CEIL(number)

CEIL()  returns  the  smallest   number  greater  than   the
parameter.

Returns:  A number

See also: FLOOR



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Example:  a:=CEIL(5.5)

          Returns the value 6.0 to the variable a.

---------------------------------------------------------------------

CHAR$(asciicode)

Returns the ASCII character whose ASCII code is asciicode.

Returns:  A one-character string

See also: CODE

Example:  t$:=CODE(65)

          Returns the letter "A", whose ASCII code is 65, to
the variable t$.

---------------------------------------------------------------------

CHARXY$(xpos,ypos)

CHARXY$() returns the ASCII code of the character  displayed
at the  screen coordinates  (xpos,ypos). The  top left  hand
corner of the screen is position (0,0) and the bottom  right
corner is position (79,24).

Returns:  A number

See also: CHAR$ ATTRXY

Example:  asciival:=CHARXY(0,0)

          Assigns the ascii value of the character displayed
at position (0,0), the top left corner.

---------------------------------------------------------------------

CLS()

CLS() clears the screen. The screen will be set to white  on
black and the cursor  position will be set  to the top  left
hand corner.

Returns:  True

Example:  CLS()


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          Clears the screen.

---------------------------------------------------------------------
CODE(character$)

Returns the ASCII  code of the  first letter  of the  string
parameter.  See appendix F for a table of ASCII codes.

Returns:  A number

See also: CHAR$

Example:  asciival:=CODE("A")

          Returns 65  to asciival,  the ASCII  code for  the
letter "A".

---------------------------------------------------------------------

COS(angle)

Calculates the  cosine  of the  angle,  where the  angle  is
measured in radians. The return  value will be in the  range
of -1  to 1.  The ACOS()  function  is used  to convert  the
cosine of an angle to the angle.

Returns:  A number

Example:  val:=COS(0.5)

          Returns 0.8775825619 to the variable val.

---------------------------------------------------------------------

CTERM(rate, end, start)

CTERM() returns the number of compound periods it would take
for the start value, at the specified interest rate to  grow
to the end  value. The  rate should  be the  specified as  a
decimal fraction rather than a percentage.

Returns:  A number

See also: FV PMT PV RATE TERM

Example:  yrs:=CTERM(0.1,100,10)




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          Returns 24.1588 interest  periods to the  variable
yrs, indicating that it would  take 24 years and two  months
for an amount of $10  to grow to $100 at  a rate of 10%  per
annum.

---------------------------------------------------------------------

DBappend(none)

Adds a new blank record to the end of the currently selected
database file.

Returns:  True if successful, False otherwise

See also: DBreplace

Example:  DBappend()

---------------------------------------------------------------------

DBavg(field$,start,end)

DBavg() returns the average of  the fields of the  currently
open database, between the specified start and end   fields.
(Note that  unlike  the  function DBcount(),  DBavg()  takes
account of zero values). Note that the specified field  must
be numeric and not string.

Returns:  A number

See also: DBcount DBsum DBavg

Example:  avg:=DBavg("AMOUNT",1,10)

          avg is assigned the average of the field  "AMOUNT"
in the current database between the first and tenth  records
inclusive.

---------------------------------------------------------------------

DBbottom()

Places  the  record  pointer  at  the  last  record  in  the
currently selected database file in index order.

Returns:  True if successful, False otherwise

See also: DBtop


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Example:  DBbottom()

          This will go  to the  last record  in the  current
database using the current index.

---------------------------------------------------------------------

DBcloseall()

Closes all  open  database and  index  files. It  is  better
practice to close each file separately using DBclosedbf().

Returns:  True if successful, False otherwise.

Example:  DBcloseall()

---------------------------------------------------------------------

DBclosedbf()

Closes the currently  open database file.  Any active  index
files will also  be closed.  It will  fail if  there are  no
files open.

Returns:  True if successful, False otherwise

See also: DBcloseall DBclosendx

Example:  DBclosedbf()

---------------------------------------------------------------------

DBclosendx(num)

Closes the index  file addressed  by the  index file  handle
num.

Returns:  True if successful, False otherwise

See also: DBusendx

Example:  DBclosendx(names)

          Closes the index file  linked to the index  handle
names.

---------------------------------------------------------------------



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DBcount(field$,start,end)

DBcount()  counts  the  fields   of  the  currently   active
database,  between  the  specified  start  and  end  records
elements, which are  nonzero, if  the field  is numeric,  or
nonempty, if the field is of type string.

Returns:  The number of nonempty fields

See also: DBavg DBsum DBcount

Example:  n:=DBcount("DONATION",1,DBreccount())

          n  is  assigned  the  number  of  records  in  the
currently open database which have nonempty DONATION fields.

---------------------------------------------------------------------

DBcountflds()

DBcountflds() returns the  number of fields  in a record  in
the currently selected database file. This function is  most
useful for determining if a call to DBstruct() would  result
in an error from too many fields in the database.

Returns:  A number

Example:  ARsize(name$[#],1)<DBcountflds()

          This line fails if the size of the name$[#]  array
is smaller than the number  of fields in the database.  This
is a  useful check  to perform  whenever an  application  is
dealing with unknown databases.

---------------------------------------------------------------------

DBdelete()

Marks the current record in the currently open database  for
deletion. It may  be physically deleted  using the  DBpack()
command and  recalled  from  deletion using  the  DBrecall()
function.

Returns:  True if successful, False otherwise

See also: DBpack DBrecall DBdeleted

Example:  DBdelete()


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---------------------------------------------------------------------

DBdeleted()

Returns True if  the current database  record is marked  for
deletion.

Returns:  True if marked, False otherwise

See also: DBpack DBrecall DBdelete

Example:  DBdeleted()

---------------------------------------------------------------------

DBexact(number)

DBexact() switches case sensitivity off, if the parameter is
zero or  on for  nonzero values.  By default,  the  database
module is  case sensitive,  to maintain  compatibility  with
dBase index files.  If you intend to  use the same  database
and  index  files   with  dBase,  you   should  leave   case
sensitivity on.

Returns:  True

Example:  DBexact(0)

          Switches case sensitivity  off, to follow the RExL
convention.

---------------------------------------------------------------------
DBgo(recnum)

DBgo() moves  the current  record pointer  to record  number
recnum in  the  currently  selected database.  The  function
returns false if  the specified record  number is less  than
one or greater than the number of records in the database.

Returns:  True if successful, False otherwise

See also: DBrecno DBskip

Example:  DBgo(DBreccount())

          This positions  the  record  pointer at  the  last
record in the currently selected database. This performs the
same action as DBbottom().


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  - Appendices.                         Page: 39 -


---------------------------------------------------------------------

DBlocate(field$,numstr,start,direction)

DBlocate() will locate  the number or  string numstr in  the
field  field$,  in  the  currently  open  database.   Unlike
DBseek(), it does not  require an index to  be open and  the
search can be  carried out  on any  field in  the file.  The
search starts from record number start and moving  backwards
if direction is negative and  forwards if zero or  positive.
In the  current release,  only numeric  and string  database
fields may be used with DBlocate().

Returns:  True if located successfully, False otherwise

See also: DBseek

Example:  DBlocate("CUST","MCCA01",0,1)

          Tries to  find the  string  "MCCA01" in  the  CUST
field of the current database starting from the first record
in the database moving forward.

Example:  DBlocate("CUSTNUM",1234)

          Tries to find the number 1234 in the field CUSTNUM
in the current database.

---------------------------------------------------------------------

DBmax(field$,start,end)

DBmax()  returns  the  maximum  value  of  the  field  named
"field$" in  the  current  database, between  the  specified
start and end records. Note that the specified field must be
numeric and not string.

Returns:  A number

See also: DBcount DBsum DBavg DBmin

Example:  q:=DBmax("PAYMENT",1,10)

          Returns, to the variable  q, the maximum value  of
the PAYMENT field in the current database between the  first
and tenth records, inclusive.

---------------------------------------------------------------------


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  - Appendices.                         Page: 40 -


DBmin(field$,start,end)

DBmin() returns the minimum value of the field specified  by
field$ in the current database, between the specified  start
and end records. The specified field must be numeric.

Returns:  A number

See also: DBcount DBsum DBavg DBmax

Example:  q:=DBmin("PAYMENT",1,10)

          Returns, to the variable  q, the minimum value  of
the PAYMENT field in the current database between the  first
and tenth records, inclusive.

---------------------------------------------------------------------

DBmkdbf(name$,num,n$[#],t$[#],len[#],dec[#])

DBmkdbf() creates a new database file name$ with num  number
of fields. The specifictions for the fields are contained in
the arrays passed  to the  function: The  first array  n$[#]
specifies the list  of field names in  the file, the  second
t$[#] defines the  types of  the fields  ("C" for  character
fields, "N" for  numeric, "D" for date  and "L" for  logical
fields), the third array contains field widths and the final
array specifies  the number  of decimal  places for  numeric
fields.

Returns:  True if successful, False otherwise.

Example:  DBmkdbf("NEWFILE",4,n$[#],t$[#],len[#],dec[#])

          Creates a database  called NEWFILE.DBF, with  four
fields as defined by the arrays.

---------------------------------------------------------------------

DBmkndx(indexname$,keyname$)

Creates an index file  for the currently selected  database.
The first parameter  specifies a  file name  and the  second
specifies a field name to index it on. The file extension of
the index file will be  ".NDX". irrespective of whether  one
was specified or not.  The index will be opened after it has
been created.



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  - Appendices.                         Page: 41 -


Returns:  True if successful, False otherwise

See also: DBusendx

Example:  idx:=DBmkndx("test","name")

          Creates an  index called  "test.ndx" which  orders
the currently selected database on the NAME field.

---------------------------------------------------------------------

DBnext()

Increments the record pointer to  the next record, in  index
order if an index  is open. It will  return an error if  the
record pointer is already at the end of the file.

Returns:  True if successfully moved, False otherwise

See also: DBprev

Example:  DBnext()

          Goes to the  next record in  the current  database
using the current index.

---------------------------------------------------------------------

DBpack()

Removes all the records in the currently open database  file
which have  been marked  for deletion  using the  DBdelete()
function.    Deleted  records   cannot  be  recovered   with
DBrecall() after a call to this function has been made.

Returns:  True if successful, False otherwise

See also: DBrecall DBdelete

Example:  DBpack()

          Deletes all records marked for deletion.

---------------------------------------------------------------------

DBprev()




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Decrements the  current  record  pointer  to  point  at  the
previous record,  in index  order if  one is  open. It  will
return an  error if  the record  pointer is  already at  the
beginning of the file.

Returns:  True if successfully moved, False otherwise

See also: DBnext

Example:  DBprev()

---------------------------------------------------------------------

DBrecall()

Undoes the  effect of  a DBdelete()  call by  resetting  the
deletion marker on the current  record. The record will  not
then be removed in a subsequent call to DBpack().

Returns:  True

See also: DBpack DBdelete

Example:  DBrecall()

          Recalls the current record from deletion.

---------------------------------------------------------------------

DBreccount()

Returns the  number of  records  in the  currently  selected
database.

Returns:  A number

See also: DBrecno DBgo

Example:  maxrec:=DBreccount()

          Sets the variable maxrec to the number of  records
in the database.

---------------------------------------------------------------------

DBrecno()




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  - Appendices.                         Page: 43 -


Returns the number  of the current  record in the  currently
selected database.

Returns:  A number

See also: DBreccount DBgo

Example:  currec:=DBrecno()

          Sets the  variable  currec  to the  current  recor
number.

---------------------------------------------------------------------

DBreindex(indexhandle)

Reindexes an  index  file  addressed  by  indexhandle.  This
command is used if you  have an index file which has  become
out of date  with respect  to its  corresponding data  file,
caused by adding or deleting records from the database while
having the index closed.

Returns:  True if successful, False otherwise

See also: DBmkndx

Example:  DBreindex(ihandle)

          Reindexes the index file  referenced by the  index
handle ihandle.

---------------------------------------------------------------------

DBreplace(fieldname$, numstr)

Writes the string or number numstr to the field specified by
fieldname$. The value will be stored accurate to the  number
of places available in  the data file, or  as zero if it  is
too large.  See the  `Introduction  to Databases'  for  more
information on how this function behaves.

The action of this function has been superseded by the  more
convenient `@' database field access notation, introduced in
version 2.10.

Returns:  True if successful, False otherwise

See also: DBrstr$ DBrnum


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Example:  DBreplace("custcode",10)

          Writes the value 10 to the CUSTCODE field.

Example:  DBreplace("custname","RH")

          Writes the string "RH" to the CUSTNAME field.

---------------------------------------------------------------------

DBrnum(fieldname$)

Returns the value of the field named fieldname$ as a number.
See the `Introduction to Databases' for more information  on
how this  function behaves.  This function  is included  for
compatibility with  earlier versions  of RExL  and has  been
superceded by the `@' and `@$' operators.

Returns:  A number

See also: DBrstr$

Example:  a:=DBrnum("custcode")

          Returns the  value of  the field  CUSTCODE to  the
variable a.

---------------------------------------------------------------------

DBrseek(dbf_handle, numstr)

DBrseek() finds  an  index key  value  of the  type  variant
parameter numstr  in the  database  file referenced  by  the
handle dbf_handle. If  the seek  value in  numstr is  longer
than the index key expression,  then the seek value will  be
truncated. If the database file has no index attached to  it
then an error will be generated and the function will fail.

This function is extremely powerful as it adds a measure  of
relational database capability to RExL.

Returns:  1 if a successful seek was performed
          2 if a partial match was located
          0 if no match could be found.

See also: DBlocate DBseek

Example:  [Expr] DBrseek(cust, "Robin")


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  - Appendices.                         Page: 45 -


          Positions the record pointer  at the first  record
in the database  file referenced  by the  file handle  cust,
which contains a key field value of "Robin".

Example:  [Expr] DBrseek(orders,@cust.orderno)

          Finds the first occurrence  (in the database  file
referenced by the  file handle orders) of  the value in  the
orderno field of the database file referenced by the  handle
cust. This   example illustrates  the  power  of  DBrseek(),
where the  contents  of one  database  can   be   used    to
retrieve  information immediately from another database.

---------------------------------------------------------------------

DBrstr$(fieldname$)

Returns the value of the field named fieldname$ as a string.
See the `Introduction to Databases' for more information  on
how this  function behaves.  This function  is included  for
compatibility with  earlier versions  of RExL  and has  been
superceded by the `@' and `@$' operators.

Returns:  A string

See also: DBrnum

Example:  a$:=DBrstr$("custname")

          Returns the  value of  the field  CUSTNAME to  the
variable a$.

---------------------------------------------------------------------

DBseek(numstr)

Finds a  matching key  value in  a numeric  or string  field
using the  current index.  A value  will be  found which  is
accurate to the fields width. If there is no index file open
and selected, then this function call will fail.

Returns:  1 if  successful, 2  for partial  match, 0  if  no
match

See also: DBlocate

Example:  DBseek(37.2)



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  - Appendices.                         Page: 46 -


          Positions the record pointer  at the first  record
in the database which contains a key field value of 37.2.

Example:  DBseek("String")

          Finds the first occurrence of the string  "String"
in the index key field.

---------------------------------------------------------------------

DBseldbf(filehandle)

Selects the database file addressed by filehandle and  makes
it the current database.   The file handle is linked to  the
file using the  DBusedbf() command.  If there  was an  index
file associated  with  the  database, then  the  index  will
automatically be selected.

Returns:  True if successful, false otherwise

See also: DBusedbf

Example:  DBseldbf(names)

          Makes the file linked to the file handle names the
currently selected database file.

---------------------------------------------------------------------

DBselndx(ihandle)

Selects an open index file,  referenced by the index  handle
ihandle,  with  which  to   order  the  currently   selected
database. The number passed is the index handle generated by
DBusendx().

Returns:  True if successful, false otherwise

See also: DBusendx DBclosendx

Example:  DBselndx(names)

          Selects the  index file  referenced by  the  index
file handle  names  and applies  it  to the  currently  open
database.

---------------------------------------------------------------------



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  - Appendices.                         Page: 47 -


DBskip(numrecs)

Skips past  the next  numrecs number  of records,  in  index
order if one is open. It will return an error if you attempt
to skip beyond the end of the file.

Returns:  True if successful, False otherwise

See also: DBgo

Example:  DBskip(1)

          Goes to the next record in index order.

---------------------------------------------------------------------

DBstd(field$,start,end)

DBstd() returns  the population  standard deviation  of  the
field$ field  in the  current database,  over the  range  of
start to end  fields. The  specified field  must be  numeric
type and not string. The deviation is calculated using the n
method (unbiased), as in the ARstd() function.

Returns:  A number

See also: DBvar DBsum DBavg

Example:  stddev:=DBstd("PAYMENT",1,10)

          Returns, to  the  variable  stddev,  the  standard
deviation of  the  PAYMENT  field in  the  current  database
between the first and tenth records, inclusive.

---------------------------------------------------------------------

DBstruct(n$[#],t$[#],len[#],dec[#])

Returns the number of fields in the currently open database.
The parameters  return a  list of  the field  names,  types,
widths and defined decimal places. The function will  return
with an error if the arrays  are not big enough to hold  the
information required.

Returns:  Number of fields if successful, False otherwise

See also: DBcountflds



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Example:  n:=DBstruct(n$[#],t$[#],len[#],dec[#])

          Returns the number  of fields in  the database  to
the variable n and places the names of the fields in  n$[#],
the field types  in t$[#], their lengths  in len[#] and  the
decimal field width of numeric fields in dec[#].

---------------------------------------------------------------------

DBsum(field$,start,end)

DBsum() returns the  sum of the  field named  field$ in  the
current database, over  the range of  start to end  records.
The specified field must be of numeric type.

Returns:  A number

See also: DBcount DBavg

Example:  sum:=DBsum("PAYMENT",1,DBreccount())

          Returns, to the sumiable sum, the sum of "PAYMENT"
field in the current database for all records in the file.

---------------------------------------------------------------------

DBtop()

Positions the  record pointer  at the  first record  in  the
currently open database.  If there  is an  index active,  it
will go to the first record in this index. An error will  be
reported if  no  database  has  been  selected,  or  if  the
database is empty when the returned value will be zero.

Returns:  True if successfully moved, False otherwise

See also: DBbottom

Example:  DBtop()

---------------------------------------------------------------------

DBusedbf(filename$)

DBusedbf() opens  a  database file  for  use and  returns  a
database file handle with which the file may be accessed.  A
database file may be made current by selecting the  database
handle using DBseldbf().


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Returns:  Database  file   handle   if   successful,   False
otherwise

See also: DBseldbf DBclosedbf

Example:  f:=DBusedbf("test")

          Opens  a  database  file  called  "TEST.DBF"   and
returns its file handle to the variable f.

---------------------------------------------------------------------

DBusendx(indexname$)

DBusendx() opens an  index file for  use with the  currently
selected database file and returns an index file handle. The
default and necessary index file extension is ".NDX",  which
is aupplied automatically  if omitted.   When the index  has
been opened using this function,  it may be activated  using
the DBselndx() command.

Returns:  Index file handle, False if error

See also: DBclosendx DBselndx

Example:  idx:=DBusendx("test")

          Returns  an  index  handle  to  the  variable  idx
through which the index file "TEST.NDX" may be accessed.

---------------------------------------------------------------------
DBvar(field$,start,end)

DBvar() returns the population variance of the field$  field
in the  current database,  over the  range of  start to  end
fields. The specified  field must  be numeric  type and  not
string. The  variance  is  calculated  using  the  n  method
(unbiased), as in he ARvar() function.

Returns:  A number

See also: DBstd DBsum DBavg

Example:  var:=DBvar("PAYMENT",1,10)

          Returns,  to  the   variable  var,  the   standard
deviation of  the  field  named  "PAYMENT"  in  the  current
database between the first and tenth records, inclusive.


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---------------------------------------------------------------------

DBzap()

DBzap()  removes  all  records  from  the  currently  active
database, irrespective of the  status of the deletion  flag.
Use this command with care!

Returns:  True if successful, False otherwise

See also: DBpack DBdelete

Example:  DBzap()

          Erases the contents of the current database.

---------------------------------------------------------------------

DEG(radianangle)

Converts from radian angle measure to degrees. Note that all
trigonometric functions in RExL use radian measure for input
and output.

Returns:  A number

See also: RAD

Example:  degangle:=DEG(0.5)

          Returns 28.64788 degrees to the variable degangle.

---------------------------------------------------------------------

DISPLAY(text$)

Displays text$ at  the current cursor  position. The  cursor
position may be set using the GOTOXY() function.   DISPLAY()
also uses five `escape sequences' (which are identical those
found in the C language).  An escape sequence consists of  a
backslash followed  by  some  character.    In  the  current
version the following escape sequences are defined:








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           Table 3.4: DISPLAY() escape sequences

\t   Move one tab stop to the right
\n   Move to beginning of next line
     scrolling the screen if needed
\r   Move cursor to start of current line
\a   Ring the terminal bell
\\   Output the backslash character

Returns:  True

Example:  DISPLAY("Hello, world\n\t")

          Displays the  string  "Hello, world",  moving  the
cursor down one line and one tab stop to the right.

---------------------------------------------------------------------

DIV(number, divisor)

Returns the  result of  the integer  division of  the  first
number by  the second.  Both parameters  must be  less  than
2,147,483,647 for this function to produce a correct  value,
otherwise an overflow will occur.

Returns:  A number

See also: MOD

Example:  x:=DIV(25,3)

          Returns 8 to the variable x.

---------------------------------------------------------------------

DTdate(year,month,day)

DTdate() takes  three parameters,  year, month  and  day-of-
month and returns the julian  day number of that date, or  0
if the date is invalid. See the section on date functions in
appendix A for information on Julian day numbers.

Returns:  A number

See also: DTdate$ DTdatevalue

Example:  days:=DTdatevalue(1991,11,2)



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          Returns the internal date number for the second of
November, 1991.

---------------------------------------------------------------------

DTdate$(daynumber)

DTdate$() will return a date string representing the date of
the Julian day number daynumber. Ensure that the date format
is set  up  correctly  by  using  the  DTformat()  function,
otherwise your application may misinterpret the date  string
returned.

Returns:  True if successful, False otherwise

See also: DTformat DTdatevalue

Example:  a$:=DTdate$(DTnow())

          If the date  is the  5th of  December, 1991,  then
this call  returns  "5/12/1991"  with European  date  format
current,  "12/05/1991"   with   American  date   format   or
"1991/12/05" with Japanese format current.

---------------------------------------------------------------------

DTdatevalue(date$)

DTdatevalue() takes a single string parameter, interprets it
as a date string according  to the current date format,  and
returns the Julian day number of that date.  Take care  that
the date format is set  correctly for your country by  using
DTformat().

Returns:  A number

See also: DTdate$

Example:  days:=DTdatevalue("2.1.1900")

          Returns 2  to the  variable days  if the  European
date is the default (2nd of January), otherwise returns 33 (
1st of February in American format).

---------------------------------------------------------------------

DTday$(date)



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DTday$() will return the name of the day specified by  date,
interpreted as a Julian day number.

Returns:  A string

Example:  day$:=DTday$(DTnow())

          Returns  the  name   of  today  (ie   "Wednesday",
"Thursday" and so on) to the variable day$.

---------------------------------------------------------------------

DTdayno(date)

DTdayno() will  return the  day-of-month for  the  specified
internal date number.

Returns:  A number between 1 and 31

Example:  d:=DTdayno(DTnow())

          Returns the number of the current day of the month
to the variable d.

---------------------------------------------------------------------

DTdayofyear(date)

DTdayofyear() takes a Julian Day Number, `date', and returns
the day number of the year in which that date fell.

Returns:  A number from 1 to 366

See also: DTdayno

Example:  d:=DTdayofyear(DTdatevalue("01-01-1992"))

          Returns 1 to d

Example:  d:=DTdayofyear(DTdatevalue("29-02-1992"))

          Returns 60 to d

---------------------------------------------------------------------

DTformat(formatnumber,time$,date$)




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Sets the  format  and separator  for  date strings  and  the
separator only for time strings.  Failure to set the  format
correctly  could  lead  to  unpredictable  results  if  your
application depends on a specific date format. Valid  values
for formatnumber are as follows:

     Table 3.5: Valid Format Specifiers for DTformat()

0    Return format in use
1    mm/dd/yyyy (American standard)
2    dd/mm/yyyy (European standard)
3    yyyy/mm/dd (Japanese standard)

time$ and date$ define the number separators for use in time
strings and date strings respectively. By default, these are
set up from  values specified in  the country  line of  your
"CONFIG.SYS" file.   If  you want  to  leave either  of  the
separators unchanged, pass the empty string, "".

Returns:  True if  valid parameters  passed and  set,  False
otherwise

Example:  DTformat(1,":","/")

          This line  sets the  current  date format  to  the
American standard  of mm/dd/yyyy,  the time  separator to  a
colon (to give  time strings like  "13:00:00") and the  date
separator to a forward slash.

---------------------------------------------------------------------

DThourno(time)

DThourno() will return the hour of the time specified by the
parameter, expressed in RExL's internal time format.

Returns:  A number between 0 and 23

See also: DTminuteno DTsecondno

Example:  d:=DThourno(DTnow())

          Returns the current hour to the variable d.

---------------------------------------------------------------------

DTminuteno(time)



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DTminuteno()  will  return  the  minute  specified  by   the
parameter, expressed in RExL's internal time format.

Returns:  A number between 0 and 59

See also: DThourno DTsecondno

Example:  d:=DTminuteno(DTnow())

          Returns the number  of the current  minute to  the
variable d.

---------------------------------------------------------------------

DTmonth$(datenum)

DTmonth$() returns  the name  of the  month upon  which  the
specified Julian day number datenum, fell.

Returns:  A string

See also: Date functions

Example:  mth$:=DTmonth$(DTnow())

          This will set mth$ to  be the name of the  current
month.

---------------------------------------------------------------------

DTmonthno(date)

DTmonthno() will return the month-of-year for the  specified
Julian day number.

Returns:  A number between 1 and 12

Example:  d:=DTmonthno(DTnow())

          Returns the  number of  the current  month of  the
year to the variable d.

---------------------------------------------------------------------

DTnow()

Returns the RExL's internal date  and time in the form of  a
real number. The  integer part of the  number is the  Julian


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day number and the decimal fraction part is the current time
of day,  expressed in  direct  fractional form.  Appendix  A
gives more information on the Julian day numbering system.

Returns:  A number

Example:  a$:=DTdate$(DTnow()) Will set a$ to be the current
date in the current date format as set by DTformat().

---------------------------------------------------------------------

DTsecondno(time)

DTsecondno()  will  return  the  second  specified  by   the
parameter, expressed in RExL's internal time format.

Returns:  A number between 0 and 59

See also: DThourno DTminuteno

Example:  d:=DTsecondno(DTnow())

          Returns the number  of the current  second to  the
variable d.

---------------------------------------------------------------------

DTsetdate(newdate)

Initializes the system  date to  the date  specified in  the
numeric parameter interpreted as a Julian day number.

Returns:  True if successful, False otherwise

See also: DTdate$

Example:  DTsetdate(DTnow()+7)

          Set the date to be one week in the future.

---------------------------------------------------------------------

DTsettime(newtime)

DTsettime() sets the system time.   The time is measured  in
decimal  fractions  of  a  day.    See  appendix  A  for   a
description of RExL's time format.



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Returns:  True

See also: DTtime$ DTtime

Example:  DTsettime(0.5) Sets the time to be midday.

---------------------------------------------------------------------

DTtime(hour,minute,second)

DTtime() takes the specified hour, minute and second  values
and returns the internal time fraction representing the time
specified. If the  time is invalid,  then the function  will
return zero.

Returns:  A time fraction

See also: DTtimevalue DTtime$

Example:  DTsettime(DTtime(13,0,0))

          This will set the current  time to one o'clock  in
the afternoon.

---------------------------------------------------------------------

DTtime$(dayfrac)

DTtime() converts the dayfrac numeric parameter from  RExL's
internal format to a time string using the currently  active
time separators.

Returns:  A string

See also: DTtimevalue DTtime

Example:  newtime$:=DTtime$(0.5)

          This will set newtime$ to be "12:00:00".

---------------------------------------------------------------------

DTtimevalue(t$)

Converts the specified time  string to RExL's internal  time
format. If the time is invalid the function returns a  value
of 0.



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Returns:  A number

See also: DTtime$ DTtime

Example:  frac:=DTtimevalue("13:00:00")

          This   will   set   frac   to   RExL's    internal
representation of one o'clock in the afternoon, 0.5416667.

---------------------------------------------------------------------

DTyearno(date)

DTyearno() will return the year for the specified Julian day
number.

Returns:  A number

Example:  d:=DTyearno(DTnow())

          Returns the  number of  the  current year  to  the
variable d.

---------------------------------------------------------------------

EQV(log1,log2)

EQV() performs  a  logical  equivalence test  upon  the  two
logical parameters  passed  to  the function.  The  function
returns True if both logical parameters are True or if  both
are False, otherwise it returns False.  Note that EQV(l1,l2)
is equivalent to NOT(XOR(l1,l2)).

Returns:  A number

See also: NOT AND XOR OR IMP

Example:  val:=EQV(TRUE(),FALSE())

          Returns False to to the variable val

---------------------------------------------------------------------

ERclear()

ERclear() clears  all  error  flags so  that  ERmsg$()  will
return a empty string and ERok() will return True, until the
next error occurs.


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Returns:  True

See also: ERwatch ERok ERmsg$

Example:  ERclear()

---------------------------------------------------------------------

ERmsg$()

Return the last error message  generated, or a empty  string
if there has been no errors since starting or since the last
use of the ERclear() function.

Returns:  A string

See also: ERwatch ERok

Example:  a$:=ERmsg$()

          Returns an  empty string  if  there have  been  no
errors since the  start of execution,  or the  last call  to
ERclear().

---------------------------------------------------------------------

ERnum()

ERnum()  returns  the  error   number  of  the  last   error
generated, or zero  if there  has been  no errors  generated
since the last  call to ERclear()  or since the  application
began.  This  function should be  used with  care since  the
error numbers may change in future versions of RExL.

Returns:  A number

See also: ERwatch ERok ERmsg$

Example:  ERnum()

---------------------------------------------------------------------

ERok()

ERok() will return true if no error has been reported  since
starting or  the last  ERclear(). It  is used  to check  for
`hidden' failures such as divide-by-0's (and so on) which do
not fail statements, and hence are more difficult to detect.


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Returns:  True if error has occurred, False otherwise

See also: ERmsg$ ERwatch

Example:  ERok()

---------------------------------------------------------------------

ERwatch(number)

ERwatch() turns the error reporting  feature on and off.  If
the numeric  parameter  is  non-zero, then  errors  will  be
displayed on the bottom line of the screen as is the default
condition of RExL. If the parameter is zero, error reporting
will be  disabled, although  the error  messages and  number
will be set up regardless.

Returns:  True

See also: ERok ERmsg$

Example:  ERwatch(TRUE())

          Enable error reporting.

---------------------------------------------------------------------

ESCWATCH(number)

ESCWATCH() is used to enable and disable the trapping of the
<Esc> and <Alt-D> keys  during execution of an  application.
In the default condition of on (a value for number of 1), an
`error' is flagged, prompting the user to see if he wants to
terminate the application.  If the parameter  is zero,  then
RExL will  not scan  for the  key.  During debugging  of  an
application, it's best to leave watching on.

Returns:  True

Example:  ESCWATCH(TRUE())

          Monitor the  <Esc> and  <Alt-D> keys  for  presses
during execution of an application.

---------------------------------------------------------------------

EXACT(num)



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EXACT() defines whether the string comparisons and tests are
carried  out  respecting  the  case  of  the  letters  being
compared (when num = 1)  or irrespective of case (num =  0).
In its default condition, RExL is not sensitive to the  case
of letters.

Returns:  True

Example:  EXACT(TRUE())

          Turns on case sensitivity.

---------------------------------------------------------------------

EXP(number)

Returns the  exponential e  (2.71828) to  the power  of  the
single numeric parameter.

Returns:  A number

See also: LOG

Example:  x:=EXP(1)

          Returns 2.718281828 to the variable x.

---------------------------------------------------------------------

FALSE()

Returns the value zero. It is used to fail a rule or part of
a rule.

Returns:  False

See also: TRUE NOT

Example:  value:=NOT(FALSE())

          Returns 1 to the variable value.

---------------------------------------------------------------------

FILL(x, y, w, h, char$)

Fills an area  of the screen  with the specified  character.
The  first  four  parameters  specify  the  horizontal   and


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vertical coordinates of  the top left  hand corner (x,y)  of
the bounding box and its width w and height h  respectively.
The fifth parameter  specifies the ASCII  character to  fill
the area with. The attributes of the box remain unchanged by
this command.

Returns:  True

See also: PAINT BOX

Example:  FILL(0,0,79,24,"A")

          Fills the screen with the letter A.

---------------------------------------------------------------------

FIND(substr$, superstr$)

Locates the first occurrence of substr$ within superstr$. If
the substring is  not in superstr$,  then the function  will
return False. The value returned is zero based, meaning that
if the substring  starts at  the first  character, then  the
return value will be zero. This behaviour is comatible  with
C language, where all string positions are zero-based.

Returns:  String index if located, -1 otherwise

Example:  pos:=FIND("lo","Hello")

          Returns a value of 3 to the variable pos.

---------------------------------------------------------------------

FLOOR(number)

FLOOR() returns  the largest  number less  than the  numeric
parameter.

Returns:  A number

See also: CEIL

Example:  a:=FLOOR(5.5)

          Returns the value 5.0 to the variable a.

---------------------------------------------------------------------



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FV(pmt,rate,periods)

Calculates the future value of equal payments of amount  pmt
of a simple ordinary annuity, earning at a periodic interest
rate for the  number of payment  periods. The interest  rate
should be expressed as a decimal rather than a percentage.

Returns:  A number

Example:  x:=FV(1000,0.1,10)

          Returns $15937.43 to the variable x.

---------------------------------------------------------------------

GOTOXY(xpos, ypos)

Positions  the  text  cursor  on  the  text  screen  at  the
specified  horizontal  co-ordinate  xpos  and  vertical  co-
ordinate ypos, taking (0,0) to be the top right hand  corner
of the screen.   If the  coordinates are  out of range,  the
GOTOXY() will return False.

Returns:  True if successful, False otherwise

See also: DISPLAY

Example:  GOTOXY(0,0)

          Sets the cursor to the top left hand corner of the
screen.

--------------------------------------------------------------------

HELP(log)

HELP() is used to turn  the online help feature on and  off.
When `log' is true, <F1>  will display the currently  active
help screen when pressed from within a dialog screen.   When
`log' is  false, <F1>  keystrokes will  be returned  to  the
application.

Returns:  True

Example:  HELP(1)

          Turns on <F1> monitoring.
---------------------------------------------------------------------


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IIF(boolexp, anstrue, ansfalse)

Returns one of the parameters anstrue or ansfalse  depending
on the value of the  boolean expression passed as the  first
parameter, boolexp. If the boolexp is true (non-zero),  then
anstrue is returned,  otherwise ansfalse  is returned.  This
behaviour is compatible with the Clipper IF command.

Returns:  Either of the second two parameters

See also: IIF$

Example:  a:=IIF(x,1,2)

          If the value of x is non-zero, then A is  assigned
the value 1, otherwise the value 2.

---------------------------------------------------------------------

IIF$(boolexp, anstrue$, ansfalse$)

IIF$()  will  return  anstrue$  if  the  boolean  expression
boolexp is true,  or ansfalse$, if boolexp  is false.   This
behaviour is compatible with the Clipper IF command.

Returns:  A string

See also: IIF

Example:  a$:=IIF$(x,"Y","N")

          If the value of x is non-zero, then A$ is assigned
the value "Y", otherwise the value "N".

---------------------------------------------------------------------

IMP(log1,log2)

IMP() performs  a  logical  implication test  upon  the  two
logical parameters  passed  to  the function.  The  function
returns True if the first  parameter is True and the  second
is False, otherwise it returns False.

Returns:  A number

See also: NOT AND XOR OR EQV

Example:  val:=IMP(TRUE(),FALSE())


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          Returns True to to the variable val.

---------------------------------------------------------------------

INIT()

Clears out all variables currently defined, setting  numeric
variables to 0.0 and setting strings to zero length.

Returns:  True

Example:  INIT()

---------------------------------------------------------------------

INPUT(x,y,w,p,value)

Generates an input field of width w and decimal precision  p
at  the  horizontal  and  vertical  coordinates  (x,y).  The
initial value of the input is value  The attribute at  (x,y)
will be extended to the width of the input. If value is  too
large to display in the  assigned area, then overwriting  of
the surrounding screen may occur.   The input area will  not
be affected by this. The maximum width of input is 19 digits
and the maximum precision is 17 digits.

Returns:  The number input

See also: INPUT$

Example:  n:=INPUT(5,10,10,2,1.2)

          Accepts the input of a number a column 5, row  10,
with a width of 10  places and including room for 2  decimal
places, with an  initial value of  1.2. The  number will  be
stored in the variable n.

---------------------------------------------------------------------

INPUT$(x,y,width,value$)

Generates a string input field of width w at the  horizontal
and  vertical  coordinates  (x,y)  specified,  setting   the
initial value of the input to value$.

Returns:  The string input

See also: INPUT


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Example:  t$:=INPUT$(5,10,10,"Test")

          Accepts input of a string at column 5 row 10, with
a width of 10 places and an initial value of "Test".

---------------------------------------------------------------------

INVERSE(x1, y1, x2, y2)

Inverts the attributes of an  area of screen. The first  two
parameters define the top left  corner. The last two  define
the bottom right corner. If you invert the same area  twice,
you will be  left with the  same area. This  can be used  to
flash an  area.    The inverse  attribute  is  generated  by
xor'ing the current attribute with 7Fh.

Returns:  True

Example:  INVERSE(0,0,79,24)

          Inverts the attributes for the whole screen.

---------------------------------------------------------------------

KBclear()

Clears all keystrokes from the keyboard buffer.

Returns:  True

Example:  KBclear()

---------------------------------------------------------------------

KBlast()

KBlast() returns the last keystroke typed by the user.   The
function can be used to determine the keystroke which caused
the termination of a dialog screen (for example, if the user
pressed <PgUp>, <PgDn>, <Enter> and so on).  If no keys have
been pressed since the application started running, or since
the last  call of  KBclear(), then  KBlast() returns  False.
See appendix D for a list of return values.

Returns:  Key code  for  last  key pressed,  False  if  none
present

See also: KBwait


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Example:  key:=KBlast()

---------------------------------------------------------------------

KBread()

Waits until  a key  is pressed  and  then returns  the  code
associated with it. If the key is a character key, the ASCII
code will be returned, otherwise, the internal code for  the
key will be returned.  See  appendix D for a list of  return
values.

Returns:  Key code for key pressed

See also: KBwait

Example:  key:=KBread()

          Waits for a key to be pressed and returns keyboard
code in the variable key.

---------------------------------------------------------------------

KBready()

KBready() returns the value of a keystroke, if one is  ready
and waiting in the keyboard  buffer. If there is no  pending
keystroke, the function returns immediately with a value  of
zero, otherwise it returns the keystroke code, as listed  in
appendix D.

Returns:  Key code for key waiting, zero otherwise

Example:  KeyWaiting:=KBready()

---------------------------------------------------------------------

KBwait(time)

Waits for the specified number of seconds time for a key  to
be pressed. The  function then returns  the coded value  for
that key or zero if no key was pressed.  See appendix D  for
a list of keystroke codes.

Returns:  Key code if key pressed, False if no key pressed

Example:  key:=KBwait()



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---------------------------------------------------------------------

LEFT$(str$,num)

Returns a  string  comprising  the leftmost  num  number  of
characters from the string str$. If the number specified  is
greater than the length of the string then the entire string
will be copied.

Returns:  A string

See also: RIGHT$ MID$

Example:  a$:=LEFT$("Hello",2)

          This sets a$ to be "He"

---------------------------------------------------------------------

LENGTH(string$)

Returns the length  of a  character string  string$. If  the
string is empty, then the value 0 will be returned

Returns:  A number

Example:  lgth:=LENGTH("System")

          This will set lgth to be 6.

---------------------------------------------------------------------

LOAD(filename$)

Loads in and  passes control to  another listing. LOAD()  is
not nested so that when the second listing finishes, control
is not  passed  back to  the  original listing.  LOAD()  may
return False if the second  listing is too big, or does  not
exist.  If the specified application image does not exist in
the current directory, then the  list of paths specified  in
the RExL environment variable will be searched in  sequence.
If the  application  is  located,  then  all  databases  are
closed, the internal error variables are reset and execution
begins at the master rule of the new application.  The stack
of screens stored by PUSHSCR() and POPSCR() are not cleared,
so screenfuls  of  information  may be  passed  between  two
applications.



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Applications  compiled  with   the  postfix  compiler   must
exercise caution  when using  the  LOAD function,  which  is
implemented slightly  differently  in  the  executable  file
library.  The section on  the postfix compiler RExLPC  gives
more details on this.

Returns:  False if listing could not load

Example:  LOAD("2ndpart")

          Loads and passes control to the application  image
with the DOS file name "2ndpart.rxl".

---------------------------------------------------------------------

LOADSCR(filename$, x, y)

Loads in  a small  area of  the  screen from  the  specified
filename. The  x  and y  coordinates  specify the  top  left
corner of where the screen is to appear. Any fields that are
contained with the  screen will  then be  activated. If  you
wish to load the screen to its original x or y position then
set the relevant parameter to  -1.  Any parts of the  screen
being loaded  which  do not  fit  will  be ignored  and  not
displayed.

Returns:  True if loaded ok, False otherwise

See also: SAVESCR

Example:  LOADSCR(n$,10,-1)

          Get the screen named n$ and place it at column  10
with the row being the same as that from where it was saved.

---------------------------------------------------------------------

LOG(number)

Returns the natural logarithm (log  to base e (2.71828))  of
the parameter.

Returns:  A number

See also: EXP

Example:  nl:=LOG(0.51)



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          This will set nl to be -0.673344553

---------------------------------------------------------------------

LOG10(number)

Returns the base-10 logarithm of the parameter.

Returns:  A number

Example:  lg:=LOG10(0.51)

          This will set lg to be -0.292429824

---------------------------------------------------------------------

LOWER$(string$)

LOWER$() returns the  parameter string  translated in  lower
case.  The  European ASCII characters are  left as they  are
and are not translated to lower case.

Returns:  A string

See also: UPPER$

Example:  a$:=LOWER$("hELlO")

          Returns the string "hello" to a$.

---------------------------------------------------------------------

MAX(num1, num2)

Returns the larger of the two numeric parameters.

Returns:  A number

See also: MIN

Example:  bigger:=MAX(5,4)

          This will set bigger to be 5

---------------------------------------------------------------------

MID$(source$, start, count)



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Returns count characters,  starting at  position start  from
the string source$. If start  is past the end of the  string
or count is less than or equal to zero, then an empty string
is returned.

Returns:  A string

See also: LEFT$ RIGHT$

Example:  a$:=MID$("ABCDEF",2,2)

          This will set a$ to be "CD"

---------------------------------------------------------------------

MIN(number1, number2)

Returns the smaller of the two parameters.

Returns:  A number

See also: MAX

Example:  small:=MIN(5,4)

          This will set small to be 4.

---------------------------------------------------------------------

MOD(number1, number2)

Returns the remainder of the division of number2 by number1.
Mathematically, this operation is known as modulo division.

Returns:  A number

See also: DIV

Example:  remainder:=MOD(10,3)

          This will set remainder to be 1.

---------------------------------------------------------------------

NOT(boolean)





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Returns  the  logical  inverse  of  the  parameter:  If  the
parameter evaluates to false, the function will return True,
otherwise it will return False.

Returns:  True or False

See also: BTnot

Example:  NOT(TRUE()) Returns False.

---------------------------------------------------------------------

OR(log1,log2)

OR() performs a logical OR  upon the two logical  parameters
passed to the function. The function returns True if  either
of the two logical parameters are True otherwise it  returns
False.

Returns:  A number

See also: NOT EQV XOR AND IMP

Example:  val:=OR(TRUE(),FALSE())

          Returns False to to the variable val.

---------------------------------------------------------------------

OScd(path$)

Changes directory to  the path  specified by  path$. If  the
directory cannot  be  accessed  then  the  function  returns
false, otherwise  true.  To  change the  current  drive  use
OSdrive().

Returns:  True if successful, False otherwise

See also: OSdrive OSrd OSmd

Example:  OScd("\rexl\demo")

          Sets the directory to be \rexl\demo on the default
drive.

---------------------------------------------------------------------

OScmd(command$)


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Allows external programs to be loaded and run. The parameter
contains the program name and  any parameters which must  be
passed to it.  OScmd() returns True if the command  executed
and False if  it failed to do  so.  Note  that RExL must  be
able to access the command  interpreter to run the  command.
The command interpreter is  usually the file  "COMMAND.COM",
located in  the root  directory of  the  boot drive  and  is
referenced by the COMSPEC environment variable.

Returns:  True if successful, False otherwise

Example:  OScmd("edit c:\autoexec.bat")

          Executes the program  or batch  file named  "edit"
and  passes  the  string   "c:\autoexec.bat"  to  it  as   a
parameter.

---------------------------------------------------------------------

OScopy(source$,dest$)

Copys a  file from  the source$  to dest$.  The  destination
parameter, unlike its  MS-DOS equivalent,  must contain  the
name of the file to which the file will be copied. The  wild
card characters ? and  are not allowed in either  parameter.
If you need  to perform a  wild card  copy, use the  OScmd()
function.

Returns:  True if successful, False otherwise

See also: OScmd

Example:  OScopy("TEST.DOC","\T.TXT")

          Copies a file "TEST.DOC" in the current  directory
to the root directory, naming it "T.TXT".

---------------------------------------------------------------------

OSdel(filename$)

Deletes the specified file from  the disk. If the file  does
not exist, or could not  be deleted then this function  will
return false, otherwise true.  filename$ may specify a  full
path including drive specifier.

Returns:  True if successful, False otherwise



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  - Appendices.                         Page: 74 -


See also: OSexists

Example:  OSdel("TEST.RXL")

          Deletes the file called "TEST.RXL" in the  current
directory.

---------------------------------------------------------------------

OSdir(mask$, attr, n$[#], sz[#], dt[#], at[#])

OSdir() is used to obtain  DOS diretory listings from  disk.
The first parameter specifies the  DOS file mask to use  for
the search and  may include  drive and  path designators  as
well as wild card characters. The second parameter specifies
the file attribute  to search for. To  search for more  than
one file  type,  add  the search  attributes  together.  The
following table gives the valid search attributes:

          Table 3.6: OSdir() File Attribute Coding

Attribute Code      Meaning
1                   Read only attribute
2                   Hidden file
4                   System file
8                   Volume label
16                  Directory
32                  Archive
64                  All files

If you  are  unsure  about  the meanings  of  any  of  these
attributes, consult your DOS manual.

The results of  the search are  placed in  the arrays:  file
names in n$[#], file sizes in sz[#], file dates and times in
dt[#] and file attributes in  at[#].  The return value  from
OSdir() is the number  of files returned in  the array.   If
any  of  the  arrays  are  not  large  enough  to  hold  the
information required,  then an  array bounds  error eill  be
generated and the function  will return without looking  for
any more files.

Returns:  The number  of files  found or  zero if  no  files
located

See also: OSexists

Example:  OSdir("*.rxl",64,n$[#],sz[#],dt[#],at[#])


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          Returns lists of all of the RExL application image
files  in   the  current directory.  The files may have  any
attribute.

Example:  OSdir("T?.RXL",64,n$[#],sz[#],dt[#],at[#])

          Returns a list  of all of  the RExL  files in  the
current directory, whose names  have two letters, the  first
of which is "T"

---------------------------------------------------------------------

OSdrive(drive$)

Selects a new current disk drive. The parameter should be  a
two character  string, the  first character  of which  is  a
drive letter and the second a colon. The return value of the
function is the ASCII character code of the drive  selected.
If the drive was not  successfully selected, then the  value
returned will be the ASCII code of the current drive letter.
Passing an empty string in  place of drive$ will return  the
current drive with no change made.

Returns:  True if successful, False otherwise

See also: OScd OSwd$

Example:  OSdrive("C:")

          Sets the current or default drive to be C:

---------------------------------------------------------------------

OSdriveok(dstr$)

OSdriveok() tests a disk drive, normally a floppy drive,  to
determine if it  is ready  to be  written to  or read  from.
`dstr$' specifies the DOS disk drive to test.  The  function
can return  one  of  a  range  of  values,  giving  explicit
information about  why  the disk  drive  is not  ready.  The
following table  gives the  exact  return values  and  their
meanings:








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  - Appendices.                         Page: 76 -


            Table 3.7: OSdriveok() return values

     -1        Wrong parameters
     0         Drive loaded and ready to read or write
     1         Drive door open or diskette inserted upside down
     2         Diskette is unformatted
     3         Write protected
     4         Undetermined

Note that  unlike  almost  all other  rexl  functions,  this
function returns zero if the test performed was successful.

Returns:  A number

See also: OSdrive

Example:  !OSdriveok("A:")

          Returns true if  drive A: is  not write  protected
and is ready for access.

---------------------------------------------------------------------

OSexists(filename$)

Checks to see  if the specified  file exists. filename$  can
contain a full pathname and drive specification.

Returns:  True if file exists, False otherwise

See also: OSdir

Example:  OSexists("c:\command.com")

          Tests to see if  the file "COMMAND.COM" exists  in
the root diretory of the C: drive.

---------------------------------------------------------------------

OSmd(dirname$)

OSmd()  will  make  a  DOS  directory.  The  single   string
parameter specifies  the  directory  name to  make  and  may
contain a drive letter.  As in the DOS  md command, you  may
only make one directory level at a time.

Returns:  True if successful, False otherwise



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  - Appendices.                         Page: 77 -


See also: OSrd

Example:  OSmd("\test")

          Makes  a  directory  called  "test"  in  the  root
directory of the current drive.

---------------------------------------------------------------------

OSnumber()

This function  returns a  value indicating  which  operating
system RExL is currently running under. Currently, the  only
value returned is 1, for MS-DOS, but future versions of RExL
running  under  different  operating  systems  will   return
different values.  Use  OSstat() to determine the  operating
system version number.

Returns:  1 for MS-DOS

See also: OSstat

Example:  sys:=OSnumber()

          Sets sys equal  to 1  if the  operating system  is
MS-DOS.

---------------------------------------------------------------------

OSrd(dirname$)

OSrd() will  remove  a  DOS  directory.  The  single  string
parameter specifies the  directory name to  be deleted.  The
string  can  contain  a  drive   letter  and  a  full   path
specification.

Returns:  True if successful, False otherwise

See also: OSmd

Example:  OSrd("c:\test")

          Removes a directory called  "\test" from the  root
directory of the C: drive.

---------------------------------------------------------------------

OSren(source$,dest$)


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This function will rename the  file named source$ to  dest$.
The parameters may specify a directory paths, so that  files
may be moved  from one directory  to another using  OSren().
Note that, as in DOS,  the destination file must not  exist,
or the function will fail.

Returns:  True if successful, otherwise False.

See also: OScopy OSdel

Example:  OSren("TEST.TXT","TEST.BAK")

          Changes  the  name  of  the  file  "TEST.TXT"   to
"TEST.BAK".

---------------------------------------------------------------------

OSstat(ar[#])

OSstat() returns  seven  items  of  information,  about  the
current  status  of  the  machine,  to  the  specified   one
dimensional numeric array.

The information returned is as follows:

            Table 3.8: OSstat() Return Indexing

Array Index    Meaning
0              Disk space free on current drive
1              Total disk space on current drive
2              Total number of disk drives available
3              Largest block of free memory available
4              Current DOS version
5              CPU type
6              Coprocessor type
7              Video adapter type

If the  current disk  is  large, then  DOS  may take  a  few
seconds to determine the its free space and total size.   If
the current disk is not  valid, for example, a floppy  drive
with an open door, then  a critical error will be  generated
and a value  of zero will  be returned for  the size of  the
disk.

The DOS version  is returned as  a real  number of the  form
x.yy where x is the major version number and yy is the minor
version number.



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  - Appendices.                         Page: 79 -


             Table 3.9: CPU Type Return Coding

Return Value   Processor Type
0              Intel 8088
1              Intel 8086
2              NEC V20
3              NEC V30
4              Intel 80188
5              Intel 80186
6              Intel 80286
7              Intel 80386
8              Intel 80486

         Table 3.10: Coprocessor Type Return Coding

Return Value Coprocessor Type
0              None installed
1              Intel 8087
2              Intel 80287
3              Intel 80387

        Table 3.11: Video Adapter Type Return Coding

Return Value   Video Adapter type
0              Monochrome
1              CGA adapter
2              EGA adapter
3              VGA adapter

Returns:  True if array large enough, False otherwise

See also: OSdir OSnumber

Example:  OSstat(Stat[#])

          Returns  the  above  information  to  the  stat[#]
array.

---------------------------------------------------------------------

OSwd$()

Returns a string containing the current directory path.  The
string will also contain the current drive letter.

Returns:  A string

See also: OSdir OScd


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  - Appendices.                         Page: 80 -


Example:  d$:=OSwd$()

---------------------------------------------------------------------

OUTPUT(device$)

Sets the default output device for print requests. Since the
string is passed directly to DOS  it can be a file on  disk.
By default the  printer output device  is the device  driver
"PRN". If you are  using a parallel/centronics type  printer
then you may wish to use the command:

                   [Expr] OUTPUT("LPT1")

or if you are using a serially connected printer:

                   [Expr] OUTPUT("COM1")

These two functions explicitly  state which type of  printer
you will be using. Using  the generic PRN device you  should
have less problems  when people connect  different types  of
printers. Making it a variable would allow you to modify  to
set up a option for the user to select the output device.

Returns:  True

Example:  OUTPUT("DUMP.DOC") Assigns all  printer output  to
the file "DUMP.DOC"

---------------------------------------------------------------------

PAINT(x, y, w, h, att, mask)

PAINT() changes the attributes of a box whose top left  hand
corner is  (x,y) and  whose width  and  height are  w and  h
respectively.  When  changing  the  attribute  byte  on  the
screen, PAINT() performs a boolean AND on the byte with  the
mask and then adds the  attribute which has been ANDed  with
the  inverted   mask.  The   result  of   this   complicated
manoeuvering is that  any color can  be filtered  in or  out
from either background or foreground. If you wish to  change
foreground only  set  the mask  to  be  240, to  change  the
background only,  set  it  to  15. If  you  want  to  change
everything in the area set the mask to be 0.

The following table  lists the colors which  can be used  on
color monitors:



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  - Appendices.                         Page: 81 -


             Table 3.12: Color Attribute Codes

     Color     Foreground          Background
     Black          0              0
     Blue           1              16
     Green          2              32
     Cyan           3              48
     Red            4              64
     Magenta        5              80
     Brown          6              96
     Light Gray     7              112
     Dark Gray      8              (128)
     Light Blue     9              (144)
     Light Green    10             (160)
     Light Cyan     11             (176)
     Light Red      12             (192)
     Light Mgnta    13             (208)
     Yellow         14             (224)
     White          15             (240)
     Blink          128            -

If the  last  screen  displayed  during  execution  had  the
flash-intensity bit set to `intensity', then a further eight
background colors, indicated above by the bracketed numbers,
are available, at  the expense  of blinking.  Note that  the
background colors are derived from the foreground colors  by
multiplying by sixteen.

Some early CGA  systems do not  support the  flash-intensity
toggle, so distribution packages which may be used on  these
adapters should not use this feature.

Returns:  True

See also: INVERSE FILL

Example:  PAINT(0,0,79,24,31,0)

          This will set the entire screen to bright white on
a blue background.

Example:  PAINT(0,0,79,24,15,240)

          This  changes  all  foreground  colors  to  white,
leaving background colors unchanged.

---------------------------------------------------------------------



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  - Appendices.                         Page: 82 -


PAUSE(time)

Halts execution  of the  application  for a  specified  time
before  execution  continues.  The   time  is  measured   in
milliseconds (thousandths of a second).

Returns:  True

Example:  PAUSE(1500)

          Halts the system for a second and a half.

---------------------------------------------------------------------

PEEK(seg,ofs)

PEEK() returns the value of the byte at the memory  location
referenced by a segment value of seg and an offset value  of
ofs.  Consult a DOS  reference if you are not familiar  with
the concept of offsets and segmentation.

Returns:  A number from 0 to 255

See also: PEEKW POKE POKEW

Example:  DisplayType:=PEEK(0,1097)

          This   expression   returns,   to   the   variable
DisplayType, the type of display attached to your  computer.
The value  will  be  3 for  a  color  display and  7  for  a
monochrome display.

---------------------------------------------------------------------

PEEKW(seg,ofs)

PEEKW() returns the  value of the  sixteen bit  word at  the
memory location referenced by a segment value of seg and  an
offset value of ofs.  Consult a DOS reference if you are not
familiar with the concept of offsets and segmentation.

Returns:  A number from 0 to 65535

See also: PEEK POKE POKEW

Example:  CharAttr:=PEEKW(47104,0)




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          This expression returns, to the variable CharAttr,
the first character and attribute  pair of a color  display.
The attribute will  be in the upper  byte and the  character
will be in the lower byte.

---------------------------------------------------------------------

PI()

Returns the value of pi, 3.14159265358979.

Returns:  True

Example:  degs:=rads*180/PI()

          Returns the value  of rads  radians, expressed  in
degrees to the variable  degs. This expression performs  the
same action as the DEG() function.

---------------------------------------------------------------------

PMT(prin,rate,periods)

Calculates  the  equal  periodic  payment  for  an  ordinary
annuity with an initial principal of prin, at the  specified
rate, for  periods  payments.  The  interest  rate  must  be
expressed  as  a   decimal  fraction,  rather   than  as   a
percentage.

Returns:  A number

Example:  amt:=PMT(1000,0.1,10) Stores the value $162.75  to
the variable amt.

---------------------------------------------------------------------

POKE(seg,ofs,value)

POKE() will  place the  byte value  at the  memory  location
referenced by a segment value of seg and an offset value  of
ofs.  This function should  be used with care, since  poking
to random areas of the computer's memory may corrupt DOS and
cause unpredictable behaviour.   Consult your DOS  reference
if you  are not  familiar with  the concept  of offsets  and
segmentation.

Returns:  True



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  - Appendices.                         Page: 84 -


See also: PEEKW PEEK POKEW

Example:  POKE(0,1047,0)

          This expression  pokes  a  value of  zero  to  the
keyboard flags byte at 0417h in the BIOS data segment.  This
will turn off insert status, caps lock and num lock.

---------------------------------------------------------------------

POKEW(seg,ofs,value)

POKEW() will place the sixteen bit word value at the  memory
location referenced by a segment value of seg and an  offset
value of ofs. Use this  function with care, since poking  to
random areas of  the computer's memory  may corrupt DOS  and
cause unpredictable behaviour.   Consult your DOS  reference
if you  are not  familiar with  the concept  of offsets  and
segmentation.

Returns:  True

See also: PEEKW PEEK POKE

Example:  POKEW(47104,0,0)

          This expression pokes a value of zero to the first
character and  attribute  pair at  the  start of  the  color
display memory area. This is displayed as a black space.

---------------------------------------------------------------------

POPSCR()

POPSCR() restores the screen from  a temporary work area  in
memory. The PUSHSCR() function is used to save the screen in
memory. Up to ten  screens may be saved  and restored, on  a
first-in, last-out or stack based basis.

Returns:  True if successful, false otherwise.

See also: PUSHSCR

Example:  POPSCR()

          Restores contents of screen.

---------------------------------------------------------------------


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  - Appendices.                         Page: 85 -


POW(number, exponent)

Returns the value of number raised to the power of exponent.
This function is included for reasons of compatibility  with
the C language.

Returns:  True

Example:  v:=POW(10,2)

          Returns 100 to  the variable  v.   Note that  this
operation can also be carried out using the `raise to power'
operator, the caret, ^, so  that the above expression  could
be rewritten as follows:

Example:  v:=10^2

---------------------------------------------------------------------

PUSHSCR()

PUSHSCR() saves the current screen in a temporary work  area
in memory. The information saved consists only of a  picture
of the screen and  does not save any  fields.  The  POPSCR()
function is used to restore a screen from memory.  Up to ten
screens may be saved and  restored, on a first-in,  last-out
or stack based basis.

Returns:  True if successful, false otherwise.

See also: POPSCR

Example:  PUSHSCR()

          Saves contents of screen.

---------------------------------------------------------------------

PV(pmt, rate, periods)

Calculates the  present  value  of equal  pmt  in  a  simple
ordinary annuity at the specified interest rate for a number
of periods. As  with all financial  functions, the  interest
rate must be expressed as a decimal fraction, rather than as
a percentage.

Returns:  A number



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  - Appendices.                         Page: 86 -


Example:  amt:=PV(1000,0.1,10)

          Stores $6144.57 to the variable amt.

---------------------------------------------------------------------

QUIT()

Halts the  execution  of  the current  application.  If  the
runtime debugger was called from within the editor, then the
editor wil be restarted,  otherwise, the module will  return
to DOS.

Returns:  N/A

Example:  QUIT()

          Halts the  application  and  then returns  to  the
operating system or editor.

---------------------------------------------------------------------

RAD(angle)

Converts an angle  expressed in degrees  into an  equivalent
angle in radians.  All trigonometric functions  in RExL  use
radians as input.

Returns:  A number

See also: DEG

Example:  r:=RAD(180)

          This  assigns  the   value  of   pi,  the   radian
equivalent of 180 degrees, to the variable r.

---------------------------------------------------------------------

RAND()

Returns a pseudo-random  number between 0  and 1. Each  time
the inference  engine  starts a  seed  set to  generate  the
sequence. Since  the seed  is always  the same,  the  random
number generator follows the same sequence. You can set your
own seed value by using the SEED() function.

Returns:  A number


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  - Appendices.                         Page: 87 -


See also: SEED

Example:  num:=FLOOR(RAND()*80)+10

          Assigns an random whole  number between 10 and  90
to the variable num.

---------------------------------------------------------------------

RATE(fv, pv, periods)

Calculates the periodic  interest rate necessary  for pv  to
grow to fv over a fixed number of compounding periods.

Returns:  A number

Example:  val:=RATE(1000,100,10)

          Assigns  the  value  0.2589  (or  25.89%)  to  the
variable val.

---------------------------------------------------------------------

REPEAT$(str$,times)

REPEAT$() returns a  string consisting of  a source  string,
str$, repeated times times. If the string would need to grow
beyond the maximum string length  of 80 characters, it  will
be truncated.

Returns:  A string

Example:  a$:=REPEAT$("-",5) Assigns the  string "-----"  to
a$.

---------------------------------------------------------------------

REPLACE$(str$,start,chars,repl$)

REPLACE$() takes a source string, str$, removes chars number
of characters  from  it,  starting at  position  start  from
within the string and inserts the replacement string,  repl$
into the  source in  that position.  If  repl$ is  an  empty
string, then the  nett effect of REPLACE$()  is to remove  a
substring from a  parent string.   If repl$  is empty,  then
str$ will be terminated at position start.




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  - Appendices.                         Page: 88 -


Note that all  string indexing  numbers (such  as the  start
parameter above)  are zero  based,  meaning that  the  first
character is as position zero, not at position one as is the
default in some other computer languages.

Returns:  A string

Example:  a$:=REPLACE$("Hello",0,2,"Ha") Assigns the  string
"Hallo" to the variable a$.  It removes two characters  from
the string "Hello", starting at position 0, giving "llo" and
inserts the  string "Ha"  at position  0 to  give the  final
string "Hallo".

---------------------------------------------------------------------

RIGHT$(str$, number)

Returns the rightmost number  of characters from the  string
str$.

Returns:  A string

See also: LEFT$ MID$

Example:  a$:=RIGHT$("Hello",2)

          Assigns the string "lo" to the variable a$.

---------------------------------------------------------------------
ROUND(number, places)

Truncates the  first parameter  to the  number of  specified
places of decimals,  or if  places is  negative, the  output
will be to that number of significant digits.

Returns:  A number

See also: FLOOR CEIL

Example:  num:=ROUND(1.546,2)

          Assigns num to be 1.55

Example:  num:=ROUND(213.2,-1)

          Assigns num to be 210.0

---------------------------------------------------------------------


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  - Appendices.                         Page: 89 -


SEED(Value)

Sets the  seed for  the  pseudo-random number  generator  in
RExL.  This  is  set,  by  default,  at  the  start  of   an
application to a constant  value (resulting in a  repeatable
array of random  numbers), but you can  make your seed  more
random by using some function of date and time.  Value  must
be in the range of 0 to 65535.

Returns:  True

See also: RAND

Example:  SEED((DTminuteno()+DTsecondno())*65535/120)

          This expression randomly assign the seed value  to
one of 120 different values.

---------------------------------------------------------------------

SIN(angle)

Calculates the sine of the angle angle, measured in radians.

Returns:  A number

See also: COS TAN RAD DEG

Example:  value:=SIN(0.5)

          Assigns the  value  0.4794255386 to  the  variable
value.

---------------------------------------------------------------------

SLN(cost, salvage, life)

Calculates the  straight  line,  or  constant,  depreciation
allowance of  an  asset  per  period.  The  first  parameter
specifies the initial cost, the second, the salvage value at
the end of the item's life and the third parameter gives the
expected life of the item.

Returns:  A number

Example:  depr:=SLN(5000,1500,5)

          Assigns 700 to the variable depr.


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  - Appendices.                         Page: 90 -


---------------------------------------------------------------------

SOUNDEX$(string)

SOUNDEX$()  calculates  the  soundex  code  of  the   string
parameter. The soundex code of a string is a four  character
string, having  an  initial letter  (equal  to that  of  the
source string) followed by a  three digit code, which  codes
for the phonetic value of that string.

SOUNDEX$() is most usually used in conjunction with database
applications, where the precise  spelling of search keys  is
not known,  or  where  there is  an  significant  chance  of
misspelling of a search key.

Returns:  A four letter string

Example:  search1$:=SOUNDEX$("smith")

Example:  search2$:=SOUNDEX$("smythe")

          Both search1$ and search2$ are assigned the  value
of "S530", the soundex code of both strings.

---------------------------------------------------------------------

SQRT(number)

Calculates the square root of  a number. The number must  be
zero or greater as the  square root of a negative number  is
undefined.

Returns:  A positive number

Example:  num:=SQRT(9)

          Assigns the value 3 to the variable num.

---------------------------------------------------------------------

STRING$(number, width, places)

Returns number converted to a string of the specified  width
and number of  decimal places. The  width must also  include
space for a decimal  point and minus sign.  If the width  is
larger than  the  resulting number  then  it will  be  right
justified. If width is less than it then the string will  be
truncated.  If  the  width  is  zero,  the  number  will  be


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  - Appendices.                         Page: 91 -


converted to the format most suitable, that is omitting  the
decimal point and  fraction if none  exists or inserting  an
exponent if the number is too large for normal display.

Returns:  A string

Example:  num$:=STRING$(-5.2,4,1)  This   will  assign   the
string "-5.2" to the variable num$.

---------------------------------------------------------------------

SUFFIX$(num)

SUFFIX$() returns  the  parameter  as  a  string,  with  the
appropriate

numeric suffix added.   This  function is  most useful  when
applied to dates.

Returns:  A string

Example:  a$:=SUFFIX$(12)

          Returns the string "12th" to the variable a$

---------------------------------------------------------------------

SYD(cost, salvage, life, period)

Calculates the sum of  the year's depreciation allowance  of
an asset for a specified of period, given the original cost,
the salvage value at  the end of its  life of life  periods.
The life is  measured in the  same units  as periods and  it
typically the number of years of expected life.

Returns:  A number

Example:  x:=SYD(1000,100,9,3)

          Returns the value 140 to the variable x.

---------------------------------------------------------------------

TAN(angle)

Calculates the trigonometrical  tangent of  an angle,  where
the angle is measured in radians.



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  - Appendices.                         Page: 92 -


Returns:  A number

Example:  value:=TAN(0.5)

          This will  assign the  value 0.5463024898  to  the
variable value.

---------------------------------------------------------------------

TERM(pmt, rate, fv)

TERM() calculates  and  returns  the number  of  periods  of
payment, each payment of amount pmt needed to reach fv at  a
periodic interest rate, rate.  The rate parameter should  be
expressed as a decimal  fraction, the percentage divided  by
100.

Returns:  A number

Example:  num:=TERM(50,0.15,5000)

          Assigns the value 19.837 to the variable num.

---------------------------------------------------------------------

TRIM$(str$,trimtype)

TRIM$()  returns  the  string  parameter  str$  with  spaces
removed from it, according  to the numeric parameter.  Legal
values for trimtype are as follows:

trimtype       Meaning
0              Remove spaces from both ends of the string
1              Remove spaces from the right end only
2              Remove spaces from the left end only

Returns:  A string

Example:  a$:=TRIM$(" <-> ",0)

          Returns the string "<->" to a$.

Example:  a$:=TRIM$(" <-> ",1)

          Returns the string " <->" to a$.

Example:  a$:=TRIM$(" <-> ",2)



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  - Appendices.                         Page: 93 -


          Returns the string "<-> " to a$.

---------------------------------------------------------------------

TRUE()

Returns the value True. If  you place this as the first  and
only line of a OR condition  in a rule, then that rule  will
always evaluate to True.

Returns:  True

See also: FALSE

Example:  TRUE()

---------------------------------------------------------------------

UPPER$(string$)

UPPER$()  returns  the  parameter  string  in  upper   case.
European accented  characters  are  not translated  by  this
function.

Returns:  A string

See also: LOWER$

Example:  a$:=UPPER$("hello")

          Returns the string "HELLO" to a$.

---------------------------------------------------------------------

VALUE(number$)

VALUE() converts a string, number$, to a number. It  returns
the converted  number if  successful or  0 if  there was  an
error.  number$ may contain exponents using the e+99 format.

Returns:  True if successful, False otherwise

Example:  num:=VALUE("5.23")

          Assigns a value of 5.23 to the variable num

---------------------------------------------------------------------



 - RExL  Version 2.11  Copyright 1992, The Software Loft -
  - Appendices.                         Page: 94 -


VERSION()

Returns  the  version  number   of  RExL  under  which   the
application is running.

Returns:  A number

Example:  ver:=VERSION()

          Sets the variable  ver to be x.yy  where x is  the
major version number and yy is the minor version number.

---------------------------------------------------------------------

XOR(log1,log2)

XOR() performs a logical  exclusive-or upon the two  logical
parameters passed to the function. The function returns True
if the two parameters are  of different logical values,  and
False otherwise.

Returns:  A number

See also: AND NOT EQV OR IMP

Example:  val:=XOR(TRUE(),FALSE())

          Returns False to to the variable val.






















 - RExL  Version 2.11  Copyright 1992, The Software Loft -
  - Appendices.                         Page: 95 -








                         Chapter 4

                    Keystroke reference


4.1  Editor keystrokes


              Table 4.1: Cursor movement keys

<F1>                Context sensitive help
<Left>              Move one character left
<Right>             Move one character right
<Home>              Move to start of input
<End>               Move to end of input
<Ctrl-Left>         Move to previous word
<Ctrl-Right>        Move to next word
<Backspace>         Delete character to left
<Del>               Delete character to right
<Shift-Enter>       Place string in scrap
<Shift-Ins>         Paste string from scrap
<Ctrl-U>            Undo changes to string
<Scroll-Lock>       Move window (if applicable)
<Alt-Equals>        Toggle macro recording
<Alt-Minus>         Select playback macro

            Table 4.2: Hilite bar movement keys

<Up>, <Down>        Move one line up and down
<PgUp>              Move up 20 lines
<PgDn>              Move down 20 lines
<Ctrl-Home>         Move to top of screen
<Ctrl-End>          Move to end of screen
<Ctrl-PgUp>         Move to to of rule
<Tab>               Expand rule definition
<Shift-Tab>         Contract rule definition
<Alt-D>, <Ctrl-Y>   Delete line
<Alt-B>             Insert blank line






 - RExL  Version 2.11  Copyright 1992, The Software Loft -
  - Appendices.                         Page: 96 -


                  Table 4.3: Modifier keys

<Ctrl-E>,<F4>  Start expression
<F10>          Select screen type
<Ctrl-O>       Make rule one-pass
<Ctrl-M>       Toggle [Multi]
<Ctrl-S>       Toggle [Single]
<Ctrl-N>       Toggle [Not]
<Ctrl-W>       Toggle [While]
<Ctrl-B>       Toggle [BackTo]
<Ctrl-Z>       Toggle [Zap]

                Table 4.4: Editor list keys

<Alt-Z>,<Shift-F2>  Rule list
     <Ctrl-R>            Rule reference list
     <Tab>               Expand and enter rule
<Alt-S>, <Shift-F3> Screen list
     <Ctrl-S>            Screen reference list
     <Tab>               Locate and position at 1st occurrence
<Alt-U>, <Shift-F4> Unused rule list
     <Tab>               Enter rule definition
     <Ctrl-Y>, <Del>, <Alt-D> Delete rule
<Shift-F5>          Unused screen list
     <Ctrl-Y>, <Del>,<Alt-D>  Delete screen from file
<Alt-V>, <Shift-F6>      Variable list
     <Ctrl-R>            Variable rule-ref list
     <Tab>               Alter array dimensions
<Ctrl-F,<Shift-F7>       Function list

            Table 4.5: Editor miscellaneous keys

<Alt-X>        Quit editor
<Alt-G>        Graphic rule display
<Alt-F5>       Show user screen
<Ctrl-F8>      Toggle breakpoint
<Ctrl-R>       Rule reference
<F2>           Save application
<F3>           Load new application
<F9>           Debug application
<Ctrl-F9>      Run application (no debugger)









 - RExL  Version 2.11  Copyright 1992, The Software Loft -
  - Appendices.                         Page: 97 -


4.2  Screen designer keystrokes


          Table 4.6: Screen designer movement keys

<Tab>          ten characters right
<Shift-Tab>    ten characters left
<Left>/<Right> one character left/right
<Up>/<Down>    one character up/down
<PgUp>         to top of screen
<Ctrl-Home>    to top of screen
<PgDn>         to bottom of screen
<Ctrl-End>     to end of screen
<Ctrl-PgUp>    to top left hand corner of screen
<Ctrl-PgDn>    to top left hand corner of screen
<Home>         to left of screen
<End>          to right of screen
<Ctrl-Right>   one word right
<Ctrl-Left>    one word left
<Enter>        next line, to right of nearest box if possible
<Del>          Delete character to right
<Backspace>    Delete character to left

      Table 4.7: Screen designer field definition keys

<Alt-F>        Display expression attached to hilited field
<Ctrl-M>       Define menu field
<Ctrl-T>       Define toggle list field
<Ctrl-R>       Define radio button field
<Ctrl-O>       Define output field
<Ctrl-I>       Define input field
<Ctrl-F>       Define new field $ Field control menu
<Ctrl-C>       Define check box field
<F10>          Edit field expression

         Table 4.8: Screen designer line draw keys

<Space>, <Right>    One character right
<Left>              One character left
<Down>              One line down
<Up>                One line up
<Enter>, <Esc>      End line draw
<Del>               Toggle delete mode
<Alt-1>             Force horizontal emphasis to one line
<Alt-2>             Force horizontal emphasis to two lines
<Alt-3>             Force vertical emphasis to one line
<Alt-4>             Force vertical emphasis to two lines



 - RExL  Version 2.11  Copyright 1992, The Software Loft -
  - Appendices.                         Page: 98 -


       Table 4.9: Screen designer miscellaneous keys

<Alt-M>        Begin block mark
<F7>           Begin block mark
<Ctrl-S>       Show screen designer status
<Ctrl-Y>       Delete characters & fields on line
               Second time, delete entire line
<F2>           Save screen
<F3>           Load new screen
<Alt-X>        Exit from screen designer
<Esc>          Exit from screen designer
<Alt-V>, <Shift-F6>      Variable list
<Alt-Z>, <Shift-F2>      Rule list
<Alt-S>, <Shift-F3>      Screen list
<Alt-L>        Enter line draw mode
<Alt-D>        Delete hilited field
<Alt-T>        Toggle flash-intensity
<Alt-R>        Remark last block

        Table 4.10: Screen designer block mark keys

<End>          Extend block mark to right of screen
<Home>         Extend block mark to left of screen
<PgDn>, <Ctrl-End>  Extend block mark to bottom of screen
<PgUp>, <Ctrl-Home> Extend block mark to top of screen
<Ctrl-PgDn>    Extend block mark to bottom-right of screen
<Ctrl-PgUp>    Extend block mark to top-left of screen
<Up>           Extend block mark one line up
<Down>         Extend block mark one line down
<Right>        Extend block mark one line right
<Left>         Extend block mark one line left
<Tab>          Extend block mark ten characters right
<Shift-Tab>    Extend block mark ten characters left
<F8>, <Enter>, <Alt-M>   Select marked block
<Esc>          Terminate block mark
<Alt-D>, <Ctrl-Y>, <Del> Delete marked block
<Alt-B>        Draw box in marked block













 - RExL  Version 2.11  Copyright 1992, The Software Loft -
  - Appendices.                         Page: 99 -


4.3  Debugger keystrokes


       Table 4.11: Debugger hilite bar movement keys

<Tab>          Expand rule definition
<Shift-Tab>    Contract rule definition
<Left>         Move cursor left one character
<Right>        Move cursor right one character
<PgUp>         Move up 20 lines
<PgDn>         Move down 20 lines
<Up>           Move up one line
<Enter>        Move down one line
<Down>         Move down one line
<Ctrl-Home>    Move to top of screen
<Ctrl-End>     Move to end of screen
<Ctrl-PgUp>    Move to top of rule

               Table 4.12: Debugger list keys

<Alt-Z>, <Shift-F2>      Rule list
<Tab>                    Expand rule definition
<Alt-S>, <Shift-F3>      Screen list
<Alt-U, <Shift-F4>       Unused rule list
<Shift-F5>               Unused screen list
<Alt-V>, <Shift-F6>      Variable list
<Ctrl-F>, <Shift-F7>     Function list

          Table 4.13: Debugger miscellaneous keys

<Alt-X>                  Quit debugger
<Alt-F5>                 Show user screen
<Ctrl-E>, <Ctrl-F4>      Evaluate expression
<Ctrl-W>, <Ctrl-F7>      Add watch
<Alt-F7>                 Animate debugger
<F4>                     Execute to cursor
<F5>                     Expand debugger window
<F6>                     Toggle windows
<F7>                     Trace execution
<F8>                     Step execution
<F9>                     Run program
<Ctrl-F9>                Remove all breakpoints and run program
<Ctrl-F8>                Toggle breakpoint
<Space>                  Trace execution
<Ctrl-O>                 Return cursor to origin
<Alt-Equals>             Toggle macro recording
<Alt-Minus>              Select playback macro
<Alt-D>, <Ctrl-Break>    Pass control to debugger


 - RExL  Version 2.11  Copyright 1992, The Software Loft -
  - Appendices.                         Page: 100 -


           Table 4.14: KB function return values

<Backspace>    8        <Left>          331     <Alt-4>          379
<Tab>          9        <Right>         333     <Alt-5>          380
<Enter>        13       <End>           335     <Alt-6>          381
<Esc>          27       <Down>          336     <Alt-7>          382
<Shift-Tab>    271      <PgDn>          337     <Alt-8>          383
<Alt-Q>        272      <Del>           339     <Alt-9>          384
<Alt-W>        273      <Shift-F1>      340     <Alt-0>          385
<Alt-E>        274      <Shift-F2>      341     <Alt-Minus>      386
<Alt-R>        275      <Shift-F3>      342     <Alt-Equals>     387
<Alt-T>        276      <Shift-F4>      343     <Ctrl-PgUp>      388
<Alt-Y>        277      <Shift-F5>      344     <Shift-Insert>   500
<Alt-U>        278      <Shift-F6>      345     <Shift-End>      501
<Alt-I>        279      <Shift-F7>      346     <Shift-Down>     502
<Alt-O>        280      <Shift-F8>      347     <Shift-PgDn>     503
<Alt-P>        281      <Shift-F9>      348     <Shift-Left>     504
<Alt-A>        286      <Shift-F10>     349     <Shift-Right>    506
<Alt-S>        287      <Ctrl-F1>       350     <Shift-Home>     507
<Alt-D>        288      <Ctrl-F2>       351     <Shift-Up>       508
<Alt-F>        289      <Ctrl-F3>       352     <Shift-PgUp>     509
<Alt-G>        290      <Ctrl-F4>       353     <Shift-Enter>    510
<Alt-H>        291      <Ctrl-F5>       354     <Ctrl-A>         601
<Alt-J>        292      <Ctrl-F6>       355     <Ctrl-B>         602
<Alt-K>        293      <Ctrl-F7>       356     <Ctrl-C>         603
<Alt-L>        294      <Ctrl-F8>       357     <Ctrl-D>         604
<Alt-Z>        300      <Ctrl-F9>       358     <Ctrl-E>         605
<Alt-X>        301      <Ctrl-F10>      359     <Ctrl-F>         606
<Alt-C>        302      <Alt-F1>        360     <Ctrl-G>         607
<Alt-V>        303      <Alt-F2>        361     <Ctrl-J>         610
<Alt-B>        304      <Alt-F3>        362     <Ctrl-K>         611
<Alt-N>        305      <Alt-F4>        363     <Ctrl-L>         612
<Alt-M>        306      <Alt-F5>        364     <Ctrl-N>         614
<F1>           315      <Alt-F6>        365     <Ctrl-O>         615
<F2>           316      <Alt-F7>        366     <Ctrl-P>         616
<F3>           317      <Alt-F8>        367     <Ctrl-Q>         617
<F4>           318      <Alt-F9>        368     <Ctrl-R>         618
<F5>           319      <Alt-F10>       369     <Ctrl-S>         619
<F6>           320      <Ctrl-Left>     371     <Ctrl-T>         620
<F7>           321      <Ctrl-Right>    372     <Ctrl-U>         621
<F8>           322      <Ctrl-End>      373     <Ctrl-V>         622
<F9>           323      <Ctrl-PgDn>     374     <Ctrl-W>         623
<F10>          324      <Ctrl-Home>     375     <Ctrl-X>         624
<Home>         327      <Alt-1>         376     <Ctrl-Y>         625
<Up>           328      <Alt-2>         377     <Ctrl-Z>         626
<PgUp>         329      <Alt-3>         378     <Ctrl-Enter>     700




 - RExL  Version 2.11  Copyright 1992, The Software Loft -
  - Appendices.                         Page: 101 -








                         Chapter 5

                       Error Messages


5.1  Error messages common to runtime and editor


5.1.1  Bad help file format

The help file has become corrupted somehow.  The only way to
remove this error is to restore a copy of the help file from
the distribution disks, or  archive file which you  received
your copy of RExL in.

5.1.2  Cannot locate system

RExL cannot shell to DOS because it cannot locate the system
files which are required.  This is most likely to be  caused
by the  COMSPEC environment  variable set  incorrectly.   It
should contain the  name, directory and  drive of your  main
command processor.   Try issuing the  following DOS  command
from the  normal DOS  prompt, if  none  of the  above  makes
sense.

set comspec=c:\command.com

5.1.3  Cannot open print file

RExL is unable to open the file which was specified  instead
of the printer. Generally, this is caused by running out  of
file handles.   This condition can  be rectified by  placing
the following line in your CONFIG.SYS file:

files=20

5.1.4  Couldn't open file

RExL is unable to open some file. Generally, this is  caused
by running  out of  file handles.    This condition  can  be
rectified by placing the  following line in your  CONFIG.SYS
file:


 - RExL  Version 2.11  Copyright 1992, The Software Loft -
  - Appendices.                         Page: 102 -


files=20

5.1.5  Macros nested too deep (20=max)

You're most unlikely to encounter this error.  It  indicates
that you are trying to  execute a macro from within a  macro
from within a  macro etc,  to a  level of  twenty deep,  the
maximum allowable.

5.1.6  Help file index is not loaded

If RExL  was unable  to locate  the  help file,  this  error
message will  be  displayed if  any  of  the help  keys  are
pressed.

5.1.7  Unable to locate help file

When the editor starts up, it preloads a portion of the help
file to allow  more rapid access to  the information in  it.
If the editor is not able to locate the help file in the  in
the  current  directory  or  the  or  list  of   directories
specified in  the REXL  environment variable,  then it  will
isue this error message.

Automatic  preloading  can  be   disabled  by  setting   the
Options|Help menu option to slow.

5.1.8  Macro recursion not allowed

RExL will not allow  a macro being defined  to call a  macro
which in turn executes the keystroke which is being defined.
This is to prevent infinite recursion of the macro facility.

5.1.9  Error loading configuration file

The  RExL  configuration  file   REXL.CFG  in  the   current
directory is invalid or could not be loaded for some reason.
The  configuration  file  format  changes  from  version  to
version, so this error may  appear if you run a new  version
of RExL without  deleting the  old configuration  file.   If
this occursm, just ignore the error and it won't re-appear.

5.1.10  Zero memory allocation request!

For some reason, a zero length request has been made to  the
memory allocator.  This should never occur, thus  indicating
a bug if  it does.   Note  down the  exact circumstances  in
which the error occurred and report it to us.


 - RExL  Version 2.11  Copyright 1992, The Software Loft -
  - Appendices.                         Page: 103 -


5.1.11  Not enough memory to perform selected operation

There is not enough memory available for RExL to do whatever
you just asked it to.   If you have any TSR programs  loaded
in memory, then unload them, re-enter RExL and try again.

5.1.12  This window is not movable

You have just tried to  move a window which is not  movable.
Generally, the only unmovable windows are the system menus.

5.1.13  No directories available

RExL is  unable to  locate any  directories in  the  current
directory for the File|Change directory menu.  This  warning
only occurs if  you are  in the  root directory  of a  drive
which has no subdirectories.

5.1.14  No files in directory

This error in a file  selection menu if the specified  drive
and directory  do  not  contain any  directories  nor  files
matching the stipulated file specification.

5.1.15  No macros defined

The Options|Save macro file menu option has been chosen  but
there are no macros currently defined in memory to be saved.

5.1.16  --- Out of memory ---

RExL has run out of memory in some critical operation  where
memory must be  present.  The  best course  of action it  to
quit RExL  as  soon as  possible,  remove any  TSR  programs
resident and to retry.

5.1.17  No screens defined

You have requested the screen list, but there are no screens
present to make the list from.

5.1.18  Not enough memory to load system

The DOS  command processor  COMMAND.COM requires  a  certain
amount of memory  to run, depending on  the version of  DOS.
If there is not enough memory present then this warning will
appear.



 - RExL  Version 2.11  Copyright 1992, The Software Loft -
  - Appendices.                         Page: 104 -


5.1.19  No unused rules available

You have  selected  the  unused  rule  list,  but  RExL  has
determined that all rules are used in the listing.  Remember
that recursive rules are taken  to be used, irrespective  of
whether they are called by  any other rules.  When  scanning
for unused rules, RExL also checks the line buffer to locate
rules, marking them as used if any are present.

5.1.20  No unused screens available

You have  selected  the unused  screen  list, but  RExL  has
determined that all  screens defined in  the current  screen
file are  used in  the listing.   When  scanning for  unused
screens, RExL also checks the line buffer to locate screens,
marking them as used if any are present.

5.1.21  No variables defined

You have  selected  the variable  list,  but RExL  has  been
unable to find any variables in its internal list.

5.1.22  Rule is not used in current listing

RExL has tried and failed to find any references to the rule
for which you  have just  requested a  reference list.  This
error can  occur from  the editor  window when  <Ctrl-R>  is
pressed, or in the rule list, with the same keystroke.

5.1.23  Error saving configuration file

RExL was unable  to save the  configuration file,  REXL.CFG,
correctly.  If a partial  file was saved, then it should  be
deleted since  it  will generate  an  error when  RExL  next
starts from that directory.

5.1.24  Screen is not used in current listing

RExL has  tried and  failed to  find any  references to  the
screen for which you have  just requested a reference  list.
This error can  occur in the screen  list, when <Ctrl-R>  is
pressed.

5.1.25  Screen file is corrupt

The screen file has somehow  become corrupted and no  longer
can be read by REXL. The  only action which can be taken  is
to restore the screen file from your last backup.


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5.1.26  Too many files open

RExL has failed when attempting  to enter a DOS shell  since
it was unable to open the command processor file because  of
lack of available file handles.  Close some files and retry.

5.1.27  Too many keys in macro (500=max)

RExL can store up to 500 keystrokes in a single macro.  This
error appears if you have  attempted to go past this  limit.
If you  require that  more than  500  keystrokes are  to  be
played back, then you should define one macro which does the
first section  and  then  calls a  macro  which  does  those
remaining.

5.1.28  Variable is not used in current listing

You have tried to get RExL to generate a variable  reference
list for a  variable which does not  have any references  in
the listing.   Note that RExL  does not  look in the  screen
file for variables, so that  a variable which is  apparently
unused may be present in some screen.

5.1.29  Wrong source file format

RExL  application  listing  files  change  format  from  one
version to another.  This error is generated if you  attempt
to load an application file  saved from one version of  RExL
into  another  version.     To  transfer  listings   between
versions, use the Import|ASCII load and save options.

5.1.30  Wrong screen file format

The editor has  attempted to load  an incorrectly  formatted
screen from a screen file.  This is usually caused by  using
different versions of RExL.   Use the Import|ASCII load  and
save menu  options to  move applications  between  different
versions of RExL.

5.1.31  Error opening screen file

RExL was unable to open the screen file associated with  the
current application.   This is  probably due  to having  too
many files open.  Close some files and try again.






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5.2  Error messages unique to editor


5.2.1  Incorrect format in listing file

RExL has found some incorrectly formatted item in the  ASCII
listing file, which  it is unable to  process.  ASCII  files
are not intended for editing with text editors and  attempts
to do so may produce errors such as this one.

5.2.2  Cannot nest fields

All field types, except menu fields, cannot nest or  overlay
each other.

5.2.3  Can only delete recursed rule from first level of
recursion

A rule which is in the rule stack cannot have lines  deleted
from it,  since  they  might  corrupt  the  rule  stack  and
possibly crash  RExL.    This error  is  generated  when  an
attempt is made to delete  a block from a recursive rule  or
to delete a line from a recursive rule.

If the line or lines must be deleted, then you should return
to the root  (by pressing <Shift-Tab>  repeatedly) and  then
entering the  rule by  selecting it  in  the rule  list  and
pressing <Tab>.

5.2.4  Unable to locate runtime module

RExL has tried  to run the runtime  and debugger module  but
was unable to find it.  When searching, RExL first  searches
the current  directory, then  the directory  or  directories
specified by the REXL environment variable, and finally  the
entire DOS path.  Only when all of these have been  searched
unsuccessfully, will this error message be displayed.

5.2.5  Area crosses fields

An attempt has been made to move or copy a block of text and
fields from one place  on the screen to  another and in  the
process overlaying  some previously  defined fields.    RExL
does not allow this and issues this message when it occurs.






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5.2.6  Can't have a field of this type in this screen

You have tried to define a field of a type not permitted  in
the current screen.   Consult the  table in  the chapter  on
using the screen designer to find out the valid combinations
of field type and screen type.

5.2.7  Illegal array dimension

When entering the  size of  an array  dimension, an  invalid
number was entered.  Re-enter the number and try again.

5.2.8  Maximum number of fields reached

Screens can contain  a maximum of  127 fields.   Any  screen
which contains more than that amount should be  re-designed,
since the screen updating  process may become noticeable  on
slow PC's.

5.2.9  Memory low, should save now!

The amount of  memory available  in RExL's  memory pool  has
gone below  2,000  bytes.    In  order  to  save  a  listing
successfully, RExL needs  about 1,000 bytes,  so saving  and
quitting now would be a good idea.

5.2.10  Not used in listing

You have tried  to enter a  rule which  is defined, but  not
used, in the current listing.

5.2.11  This is the main rule and is called to start the kbs

You have  attempted to  find rule  references for  the  main
program rule. This is only a diagnostic message.

5.2.12  Cannot change rule name to one already existing

Normally, RExL allows for and automatically compensates  for
the changing of the name of any rule in an application.   It
does not, however, allow  a rule name to  be changed to  one
which exists already, since a name conflict would arise. Any
changes made to the rule name are undone.







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5.2.13  This screen already exists

As with rule names previously, it is not possible to  change
the name  of a  screen to  one  which already  exists.   Any
changes made to the screen name are undone.

5.2.14  Toggle fields must be more than 5 and less than 75
characters wide

The width  of  toggle  fields  must  be  between  6  and  74
characters inclusive.

5.2.15  Unable to create screen file

RExL was  unable to  create a  screen  file to  go with  the
current application.   This  is  probably caused  either  by
having no  disk space  left, or  by having  no file  handles
available.


5.2.16  Error saving file

RExL was,  for  some  reason, unable  to  save  the  current
application to disk successfully.   This is probably  caused
either by having no  disk space left, or  by having no  file
handles available.

5.2.17  Error loading file

RExL was, for  some reason,  unable to  load an  application
from disk successfully.  This  is probably caused by  having
no file handles available.

5.2.18  Error loading screen file

RExL was unable to load the screen file associated with  the
current application.

5.2.19  Cannot change name of Main Program

It is  not possible,  in the  current  version of  RExL,  to
change the name of the root rule.








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5.3  Error messages unique to runtime-debugger


5.3.1  Array bounds overflow

The runtime  module has  detected an  attempt to  access  an
array element beyond the defined bounds of the array.  Array
bounds can be set  in the editor from  the variable list  by
selecting the array, pressing <Tab> and entering the size of
the array.

5.3.2  Can't set a breakpoint here

A breakpoint can only be  set on a line which will  actually
be  executed.    These  lines  include  rules,  screens  and
expressions but do not include blank lines.

5.3.3  Cannot open printer for output

Cannot write to print device
Cannot close print device ,

The printer device cannot be  opened for output, written  to
or closed.  If output is directed to the printer, then  make
sure that it is connected and online.  Alternatively, if the
printer destination has been set using the OUTPUT() command,
then make sure that the filename is valid.

5.3.4  Cannot find editor

You have run the debugger from the editor or you have passed
the -e  option on  the command  line,  but the  debugger  is
unable to locate  the editor.   The debugger will  terminate
when this  message  is  cleared.   When  searching  for  the
editor, RExL searches the current directory, the directories
specified in  the REXL  environment directory  and then  the
entire DOS path.

5.3.5  Divide by zero

Your  application  has  attempted  a  to  divide  a  numeric
expression by  zero,  which  is  a  computationally  invalid
operation.

5.3.6  String-numeric collision

This error should never occur  in normal operation of  RExL.
It indicated  that an  internal parsing  error has  occurred


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during the assignment  of some quantity of  to another.   If
you receive this error, then contact us.

5.3.7  Can't have string for radio button parameter

Only numeric variables are valid radio button LValues.  This
error is  kept for  reasons  of compatibility  with  earlier
versions of RExL.

5.3.8  Stack underflow

This error  should not  occur.   It  indicated that  one  of
RExL's  internal  stacks  (numeric,  string  or  array)  has
underflowed.  If you receive this error, then contact us.

5.3.9  Stack overflow

This error  should not  occur.   It  indicated that  one  of
RExL's  internal  stacks  (numeric,  string  or  array)  has
overflowed.  If you receive this error, then contact us.

5.3.10  Numeric value out of range

Certain mathematical functions require that their parameters
be within certain ranges.   For example, the LOG()  function
is only defined for values  greater than zero, and  attempts
to find logiarithms  of numbers  less thanor  equal to  zero
will generate this error.

5.3.11  Rule stack overflow

You have  tried  to  recurse beyond  the  maximum  limit  of
recursion.   By default,  the limit  is 100  entries on  the
stack, but it can be increased from within the editor  using
the Options|Rule stack menu option  or by specifying the  -s
option on the command line to the debugger.

5.3.12  Invalid database file handle

An operation  involving  database  file handles  has  failed
because an  invalid file  handle was  passed.    This  error
generally occurs in expressions using RExL's @variable.field
construction, when  <variable>  does  not  contain  a  valid
database file handle.






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  - Appendices.                         Page: 111 -


5.3.13  Unable to allocate rule stack

The runtime and debugger module has been unable to  allocate
enough memory to the runtime stack and consequently will not
attempt to run the application.   Make sure that you're  not
passing some over-large  value to the  module either on  the
command line, with the -s option, or from within the  editor
using the Options|Rule stack option.

5.3.14  Math error : Parameter out of range in function XXX

The function XXX has been passed a value which is out of the
range for  which the  function is  defined.   The  functions
which can  generate this  error  are SIN(),  COS(),  ACOS(),
ASIN(), TAN(), ATAN(), LOG() and LOG10().

5.3.15  Math error : Parameter singularity in function XXX

Certain functions, while defined across certain ranges  have
values within the range for which the return value generates
a singularity.    For example,  the  TAN() function  is  not
defined for PI/2  radians and an  attempt to calculate  this
value would cause this error to be generated.

5.3.16  Math error : numeric overflow

You have tried to generate a result greater than the maximum
value which RExL can cope with, about 2.7E308, absolute.

5.3.17  Math error : numeric underflow

This error indicates  that the result  of a calculation  has
underflown and cannot  be represented accurately.  Generally
speaking, a numeric underflow will return a zero value.

5.3.18  Math error : precision loss

This error indicates that a calculation has not been carried
out to  a sufficient  degree of  accuracy.   This  generally
occurs  when   evaluating  functions   close  to   parameter
singularities.


5.4  Critical Errors


These errors occur  when some item  of hardware attached  to
your PC does not appear to be functioning correctly.   These


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errors are entirely  DOS generated  and RExL  itself can  do
little to  rectify  them.   Like  the other  error  messages
above, these are trappable using the ERok() function.  These
errors are  listed in  increasing order  of obscurity,  with
errors at the bottom of the list being the most unlikely  to
occur.

5.4.1  Write protect error

An attempt has  been made to  write information  to a  write
protected disk.   Remove  the   write  protect tab  and  try
again.

5.4.2  Drive not ready

The disk drive accessed in the last operation was not ready.
Make sure that the disk  is inserted correctly, is  properly
formatted and can be read from the drive.

5.4.3  Printer out of paper

The printer  device  has  returned  an  error  code  to  DOS
indicating  that  something  was  wrong  with  the  printer.
Possible causes include no paper in the printer, the printer
being turned off or off line or a paper jam.

5.4.4  Write fault

DOS has tried  to write to  some block  or character  device
driver but  the driver  returned an  error code,  indicating
that it was unable to  perform the operation.  When  applied
to printers, it generally means that the printer has run out
of paper or has been turned off during a print run.

5.4.5  Read fault

DOS has tried  to read from some  block or character  device
driver but  the driver  returned an  error code,  indicating
that it was unable to perform the operation.

5.4.6  General Failure

This is a  general purpose catch-all  error message,  saying
that something went wrong, but DOS was unable to figure  out
exactly what.   When applied  to disks,  it generally  means
that the disk is not formatted or is not of the correct size
for the disk drive.



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5.4.7  Sector not found

This error indicates that a sector on a  disk has been found
to be invalid, probably caused by a corruption of some  type
on the disk in question.

5.4.8  Unknown unit

A request has been made by DOS to some device which does not
exist or has not responded.

5.4.9  Unknown command

An IOCTL request  has been made to  some block or  character
device driver  but the  command was  not recognised  by  the
driver.

5.4.10  CRC error

The cyclic redundancy  check on  disk reads  and writes  has
failed, indicating a  faulty drive  or improperly  formatted
disk.

5.4.11  Bad request structure length

An IOCTL request  has been made to  some block or  character
device driver but  the format  of the  request structure  is
incorrect.

5.4.12  Seek error

BIOS was unable to locate the disk sector requested in a DOS
call.

5.4.13  Unknown media type

The disk which has just been accessed does not have a  valid
media identifier.  This is usually caused by using Unix (and
other system) formatted floppy disks.











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                         Chapter 6

                      Extra Utilities


This appendix documents  the extra  utilities supplied  with
RExL which  are  only  available  in  the  fully  registered
version.


6.1  RExLPC


RExLPC is a  utility which will  combine a RExL  application
image file, its  associated screen file  and a special  stub
file into a single standalone executable file, suitable  for
distribution.  It  is provided  as a  neater alternative  to
RExLRT, described  further on  in this  chapter.  Typically,
RExLRT is  used  to  distribute applications  which  can  be
modified  by   the   end-user,   or  may   require   on-site
modification by the  developer.  On  the other hand,  RExLPC
can be  used  to provide  a  single, faster  DOS  executable
application which  cannot  be  decompiled.  Backups  of  the
original versions of  the application must  be kept if  they
may need to be modified at a later date

As a  rough guide  to performance  gains, RExL  applications
converted with  RExLPC will  run code  approximately two  to
four times as fast as REXLRD and REXLRT will.  Corresponding
C programs will  run about  half as  fast to  twice as  fast
again.   For database  operations, the  speed gain  will  be
small because most time is  spent within the database  code,
which is common both the stub and the other executables.

RExLPC takes two parameters on  the command line, the  first
specifies the RExL application  file to be converted,  while
the second parameter specifies the DOS executable file to be
created.  The base stub file REXLSTUB.COD must be accessible
either through the REXL environment  variable or on the  DOS
PATH.   While  the postfix  compiler  is running,  it  posts
progress reports on the screen, to keep you informed of  how
far it  has  got.    When the  compiler  finishes,  it  will


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generate an  executable  file  as specified  by  the  second
command line parameter.  If an executable file of this  name
exists already, then  it will  be overwritten.  Applications
should be fully working and debugged when passed through the
compiler.

The resulting executable file can be copied, distributed and
run like any other DOS executable.

The process involved in conversion is as follows.   Firstly,
the screen file and application images are loaded as  normal
and  the  stub  file  is  copied  to  the  specified  output
executable file.  Then the postfix compiler module  postfix-
compiles the application and  appends the generated code  to
the stub file.  Finally, the screen file is postfix compiled
and then appended  to the  stub.   The resulting  executable
file can be copied, distributed  and run like any other  DOS
executable and does not require any of the files (which were
required to build it) to be present when the program is run.
As with  all other  RExL executable  files, you  should  not
attempt to  compress  the  file  with  compressors  such  as
PKLite, DIET, LZexe and such  like because of the nature  of
the files.

Finally, a minor point of incompatibility with RExL:  RExLPC
does not supports the LOAD() function as it exists in  RExL,
because of the different .RXL and .EXE internal formats.  In
the compiled version, the LOAD()  function will look for  an
executable file of  the same name  as the application  image
and load and  execute that instead.   This  seems to be  the
most acceptable  solution  and  will work  transparently  if
multiple  applications   are   converted   and   distributed
together.  If  this is  not satisfactory,  then the  OScmd()
function can be  used to run  the runtime  (or the  runtime-
debugger module), passing it the name of the application  to
run.

For example,  the  command  LOAD("TEST")  which,  in  normal
circumstances  would   load   an  application   image   file
"TEST.RXL", would be interpreted by RExLPC as a call to load
and  run  the   file  "TEST.EXE",   overlaying  the   caller
application (unlike a call to OScmd(), where the application
regains  control  when   the  called  program   terminates).
Alternatively, the command OScmd() could be used to run  the
application using a call such as: OScmd("rexlrt test").





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6.2  RDU


6.2.1  Introduction

RDU, the  RExL Database  Utility, is  a standalone  database
manager which can  be used to  manage dBase III+  compatible
files.  It can create  and modify database structures,  edit
and browse database files and create and maintain dBase III+
index files.

RDU is quite simple  to operate and is  based upon the  same
interface as other RExL programming tools.

6.2.2  Loading and Running

RDU is loaded  by typing  RDU at  the DOS  prompt and  needs
about 180k  of  DOS memory  to  run.   To  start work  on  a
database file  immediately, rather  than having  to use  the
menu system to load one, you can simply pass the name of the
database on  the command  line.   For example,  to load  and
start work on a database named "CUSTOMER.DBF", issue the DOS
command `RDU customer'.  The default and necessary extension
of ".DBF" will  be automatically  appended for  you, so  you
don't need to specify it.

When RDU  has  loaded, you'll  be  presented with  the  main
screen which is similar to RExL's editor.

There are five  pull down  menus in  RDU which  are used  to
control the program.   The next  five sections will  explain
each menu.

6.2.3  RDU menu system

6.2.3.1  File Menu

There are seven  options in this menu,  based upon those  in
the File Menu of RExL's editor.  The options are as follows:

    o  Use File: When selected, this option pops up a dialog
       box prompting for a database  file to open.  You  can
       either  enter  a  database  name  directly  or  press
       <Enter> and select from a list.  When a database file
       has been selected,  it can be  edited using the  Edit
       menu.




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    o  Use Index:  When  a  database  has  been  opened  and
       selected, an index file can  be opened, to order  the
       contents of the  database. When this  menu option  is
       selected, a file name  dialog box appears,  prompting
       for an index  file to  open.   As with  the Use  File
       option, an  index name  can be  entered directly  or,
       upon pressing <Enter>, an  index file can be  selcted
       from a list. If there is no database open, then  this
       option cannot be used.

    o  Remove: This choice allows you to delete a file  from
       disk. You may need to do  this is you want to save  a
       file on disk, but are unable to do so through a  lack
       of disk space.

    o  Change Dir: This option will allow you to change  the
       active directory.  The format  used here is much  the
       same as that used in the file name input routine, the
       only  differences  being  that  no  file  names   are
       displayed in  the list  and that  the current  active
       path  (drive  name  with  full  directory)  will   be
       displayed on the  status line  at the  bottom of  the
       screen.

    o  Default Drive:  When this  option is  chosen, a  menu
       will pop up displaying the list of available DOS disk
       drives. As with  the directory  selection above,  the
       current  active  path  is  displayed  on  the  status
       display line at the bottom of the screen.

    o  OS Shell: If you  want to run a  DOS command, but  do
       not wish to  exit from RDU  permanently, choose  this
       option to go into a  DOS shell. While you are in  the
       shell, you should not,  under any circumstances,  run
       any T$SR programs (such  as Sidekick, ScrGrab and  so
       forth), since these programs change critical area  of
       the computer's  memory which  may cause  it to  crash
       unpredictably when you  return to RDU.  When you  are
       finished in the shell, type `exit' at the DOS  prompt
       to return.

    o  Quit: This option terminates  RDU and returns you  to
       DOS permanently.  Since any  work done is written  to
       the database immediately, there is no `File has  been
       changed' type prompt  generated when  this option  is
       selected.




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6.2.4  Edit Menu

This six  option menu  is used  to control  the editing  and
deletion of  information  in  the  database  file  currently
selceted.   If there  is no  database  file open,  then  the
options in this menu may not be used.

The first  two  options,  edit  and  browse,  are  used  for
changing and viewing information in the current database and
are both `variations on a theme'.  In either of these modes,
the fields in  the database are displayed  on the left  hand
side of  the  screen and  the  contents  of the  fields  are
displayed to the right of the field names.

The <PgUp> and <PgDn> keys are used to move to the next  and
previous records respectively,  while <Ctrl-PgUp> moves  the
record pointer to  the top of  the database and  <Ctrl-PgDn>
moves it to the last record.

If there are more fields in the database than can be  fitted
on the screen, then <Ctrl-Home> moves the first field in the
database to the  top of the  screen, while <Ctrl-End>  moves
the last field to the bottom line of the screen.

In browse mode, it is  not possible to edit the contents  of
the database  and  there  is therefore  no  cursor  visible.
Pressing <Up> and <Down>  will move increment and  decrement
the top field on the  screen, if there are more fields  than
can be fitted, otherwise the  keys have no effect in  browse
mode.

In edit mode, <Up> and <Down> move to the previous and  next
fields in the database, scrolling the field list, if needed.
<Tab> and <Shift-Tab>  perform the same  action as <Up>  and
<Down>.  If <Down> or <Enter> is pressed on the final  field
in the  record, when  the record  pointer  is at  the  final
record in the database, then the prompt Append records? will
appear.  If the Yes  option is selected, then a record  will
be appended to  the database and  editing will proceed  from
the new record. If the no option is selected, then no record
will be added.

When editing date fields, the date entered will be displayed
and must be entered in the format appropriate to the country
set up on your machine.  If a valid date is entered, then it
will be silently  converted to a dBase  date and written  to
the database  file.   RDU will  not  allow you  to enter  an
invalid date.


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Logical fields are one character wide and treat values of Y,
y, T and t as true and all other characters as false.   True
values are  stored  as  Y  and false  values  as  N  in  the
database.

Character fields may be from  1 to 255 characters wide.   If
the field width of the field being edited is greater than 67
characters, then a small arrow will be displayed before  the
start of  the edit  area.   The arrow  can be  one of  three
characters, depending on  whether the edit  area extends  to
the  left  of  the  currently  displayed  area  (uses  ASCII
character 27), whether it extends on both sides (uses  ASCII
character 29), or whether it extends to the left (uses ascii
character 26).

Any changes made  to the database  file are  written to  the
file immediately.

The six options in the Edit menu are as follows:

    o  Edit record:  Enters  RDU's record editing  facility,
       as described above.

    o  Browse record: Enters RDU's record display  facility,
       as described  above.  The  contents of  the  database
       cannot be changed when using this mode.

    o  Delete record:  This option will set the delete  flag
       of the  current  record.    Because  this  option  is
       relatively common, the <Alt-D> keystroke can be  used
       to toggle  this flag.   Note  that when  a record  is
       marked for  deletion, it  is not  physically  removed
       from the database.

    o  Recall deleted record:  This option clears the delete
       flag for the current record in the current  database.
       <Alt-D> can be  used to clear  the delete  flag on  a
       record, if it has been set.

    o  Pack database:  All records marked for deletion in  a
       database will be  removed when it  is packed.   After
       this operation, the records  cannot be recalled  from
       deletion using the Recall menu option.

    o  Zap database:  This  menu option permanently  removes
       all records  in  a  database. As  with  packing,  the
       records cannot be retrieved afterward.



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6.2.5  Search Menu

The search  menu  is used  for  searching for  and  locating
information in database files.   There are three options  in
this menu:

    o  Locate string: This option is  used to search for  an
       occurrence of a string within a field in the  current
       database.

       When the  option  is  chosen,  a  menu  will  pop  up
       containing the names of all the fields in the current
       database.  The  field selected here  will be the  one
       searched in during the  searching operation.  Once  a
       field has  been selected,  a dialog  box will  appear
       prompting for a string to  locate.  The dialog  input
       area will be as wide as the field being searched in.

       When a  search string  has been  entered, the  record
       pointer will  be reset  to the  top of  the file  and
       searching will  begin  from there.    If a  match  is
       found, then the matching record will be displayed and
       a prompt box will  appear, asking whether the  search
       should continue  from that  location to  try to  find
       another occurrence of the string.

       The record counter in the bottom right of the  screen
       is constantly updated during  the search to keep  you
       informed of its progress.

    o  Seek string: This  option is used to  seek for a  key
       string in an index file.  When selected, a dialog box
       appears, prompting for a string to seek for.

       If the seek  is successful, then  the record  pointer
       wil be  placed at  the  record whose  key  expression
       matches that entered.  If it is unsuccessful, then an
       error message will be displayed.

       Since records are in index  order when an index  file
       is open, you  will not  be prompted  to continue  the
       seek when it has successfully found something.

    o  Go to record:  This  option will prompt for a  record
       number to jump to.  If the record number specified is
       less than 1 or greater than the number of records  in
       the  database,  then   no  action   will  be   taken.
       Otherwise, the  record pointer  will  be set  to  the


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       specified record number.   The record  number is  not
       dependant on any index files open.

6.2.6  Utilities Menu

This menu has six options as follows:

    o  Create  database:  This  option  is  used  to  create
       database structures.  When  it  is  first  chosen,  a
       dialog box appears prompting for a file name to  call
       the structure which is about to be created.  When one
       has  been  entered  the  creation  of  the  structure
       begins.

    o  The structure creation  box has four  columns in  it.
       The first is  for field names,  the second for  field
       types, the  third  for  field widths  and  the  final
       column for field decimal places.

    o  For logical and date fields, the field width is fixed
       at one  and eight  characters respectively,  with  no
       decimal places.  The dialog will not allow figures to
       be entered in  the final  two columns  for these  two
       field types.  Similarly, it is not possible to  enter
       decimal field widths for character fields.   RDU will
       not allow duplicate field names  to exist in a  file,
       displaying an error if this is attempted.

    o  The keystrokes used are as follows:

             Table 6.1: Keystrokes in structure create

       <Shift-Tab>    Go to previous input area in field
        <Tab>         Go to next input area in field
        <Enter>       Go to next input area, creating field
                      if already on last input area
        <Up>          Go to same input area in field above
        <Down>        Go to same input area in field below
        <Alt-D>       Delete field definition

    o  The field type  can be toggled  by pressing  <Space>.
       Alternatively, pressing  the field  type letter  will
       set the type:  `C' for character fields, `D' for date
       fields, `N' for  numeric fields and  `L' for  logical
       fields.





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    o  When the field definitions have been created, move to
       the final field in the structure and press <Enter> to
       create the strucure on disk.

    o  Once the  structure has  been created,  the  File/Use
       database menu options can be used to open and  select
       the file just created.

    o  Modify structure  This choice operates in exactly the
       same way as the previous option for creating database
       files.  The structure of the current database will be
       placed in the database creation  box where it can  be
       modified using the same keystrokes as before.

    o  If the type of a  field is changed, then RDU will  do
       its best to preserve the  contents of the field.   In
       particular, date fields  converted to numeric  fields
       will  have  their  contents  changed  to  Julian  day
       numbers, used elsewhere in RExL, while numeric fields
       (changed to  date fields)  will  be assumed  to  hold
       Julian day numbers and processed accordingly.

    o  If the  width  of  any field  is  reduced,  then  the
       contents will be  truncated to  fit.   If numbers  in
       numeric fields  no  longer  fit, then  they  will  be
       replaced with asterisks.

    o  When the desired changes have been made to the  file,
       press <Enter> on  the empty field at  the end of  the
       list to make the changes permanent.

    o  Create index: This choice is used to create an  index
       file for the database which is currently open.   When
       this menu option is selected, you will be prompted to
       enter an index key expression, which may contain  any
       of the dBase III functions supported in RExL and  the
       fields in  the  current  database.    As  an  aid-de-
       memoire, <F10> lists the fields in the database while
       <Ctrl-F> can be used to list the functions  available
       to you.  If the expression entered is not valid, then
       an error will be generated.

    o  When a syntactically valid  index key expression  has
       been entered, you  will be  prompted for  a DOS  file
       name to save the index file under. If one is entered,
       then index generation will proceed.




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    o  While the index file is being generated, its progress
       will be displayed in a progress box in the center  of
       the  screen.    Because   of  the  method  used   for
       generation of index files, sorting may be slow if the
       file is already in order, however, if the file is not
       sorted,  then  the  index  will  be  generated   very
       rapidly.

    o  Reindex:   This option  will reindex  an index  file.
       This operation  may  need  to be  carried  out  if  a
       database file has been modified while its  associated
       index file was closed.  If there is no database  file
       or index  file open,  then  this option  performs  no
       action.

    o  Statistics:   This option  displays statistics  about
       the database  and index  files currently  open.   The
       first line displays the name of the current database,
       the second  displays the  name of  the current  index
       file, if one is open.

    o  The third and fourth lines show the number of  fields
       and records, respectively, in the database. The fifth
       line displays  the date  of the  last update  to  the
       database file, while the final line shows the size of
       the database header record.

    o  Field list:  This  option  lists the  fields  in  the
       current database. The display  format is exactly  the
       same as  in the  database create  option above,  with
       field names in the first column, types in the second,
       widths in the third and decimal places in the fourth.

6.2.7  Options Menu

This menu is fundamentally the  same as that in the  editor.
It has five options as follows:

    o  Load macros:  Any macro definitions you define may be
       saved to  disk for  later retrieval  using this  menu
       option. The macro file format is constant across  the
       RExL product  range, so  that macros  defined in  the
       editor may be used in the debugger or in the database
       manager and  so on.   Macros  are explained  in  more
       detail at the start of the chapter on the editor.





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    o  Save macros:  This option  allows you to save  macros
       which can then be reloaded at some future time  using
       the load option above.

    o  Beep  off:    By  default,  RExL  beeps  whenever  it
       encounters an error. This  beeping can be toggled  on
       and off by selecting this option.

    o  Exploding windows In its normal state, all windows in
       RExL open  instantaneously  upon  activation.    This
       option can be  used to  make windows  `grow' to  full
       size on the screen.  This is only a visual effect and
       has no effect upon the application.

    o  Case sensitivity:  By  default, all database  indexes
       and searches are  carried out  with case  sensitivity
       on, to follow the dBase convention.  However, this is
       contrary to  the case-insensitivity  in the  rest  of
       RExL.  If dBase  compatibility is not required,  then
       the case sensitivity  may be turned  off.  Note  that
       the  case-sensitivity   feature  only   affects   the
       generation of index files.


6.3  RExLRD


RExLRD is the combined runtime  and debugger module for  the
RExL programming  environment and  is called  by the  editor
whenever the application is run.  RExLRD uses the  following
command line syntax:

            RExLRD [-d] [-k] [-e] <filename.rxl>

The options are used as follows:

    o  -d:
       The `d' parameter will cause the debugger to start up
       in debug mode,  as if  the user  had pressed  <Alt-D>
       during loading of  the application.   This switch  is
       passed  invisibly  by  the  editor  to  the  debugger
       whenever  the  debugger  is  called  via  the   Debug
       application option in the Run menu in the editor.

    o  -e:
       The `e' option will return control to the editor when
       the debugger terminates.   Whenever the editor  calls
       the debugger, this option  is silently passed to  the


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       debugger, so  that the  debugger will  return to  the
       editor when it terminates.

    o  -k:
       This `k' option  is used to  tell the runtime  module
       not to watch  out for the  two keystrokes of  <Alt-D>
       and <Esc>,  which  are normally  monitored.  (<Alt-D>
       will interrupt the run module and relinquish  control
       to the  debugger  while  pressing  <Esc>  twice  will
       terminate the application.)

    o  -l:
       This `l' option  is used to  tell the runtime  module
       that it is  running on an  LCD display.   If you  are
       running the  debugger  from  the  editor,  then  this
       option will be passed  automatically, but if you  are
       running it from the DOS  command line, then you  need
       to include it specifically.

    o  -s:
       This `s'  option  is used  to  set  the size  of  the
       runtime  stack  to   be  used   when  executing   the
       application.   Be  default  the  size  is  100  stack
       entries, but if your application uses recursion  then
       this value should be increased.  If you need as  much
       memory as posible,  then this value  may be  reduced:
       Each stack entry  requires eight  bytes of  permanent
       storage.  The required stack size is placed after the
       `s'.  For example, to set a stack size of 30 entries,
       the command line option `-s30' should be passed.


6.4  RExLRT


RExLRT  is  the  runtime  module  of  the  RExL  programming
environment.  If it used for running the systems written  in
RExL. It  is  about  one-third  smaller  than  the  combined
runtime-debugger module and it  runs applications about  10%
to 15%  faster.  The  command  line  syntax  for  RExLRT  is
identical to that for the debugger, with the only difference
being that <Alt-D>  does not pass  control to the  debugger,
since there is none.

RExLRT  is  used  in  preference  to  the  executable   file
generator, RExLPC described earlier, when it is necessary to
have  separate  application  image,  screen  and  executable
files.   Typically,  this  program  is  used  to  distribute


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unfinished   applications   which   may   require    on-site
modifications.

Note also, that  REXLRT supports the  LOAD() function  call,
whereas RExLPC does not,  because of the differing  internal
formats.


6.5  ScrList


ScrList lists the contents of  screen files and outputs  the
contents to the standard output device, usually the monitor.
The format of the output file listing is as follows:

The block  number  of every  block  in  the screen  file  is
printed first,  immediately followed  by a  colon.   If  the
block is in use  as a screen, then  the screen name will  be
printed surrounded by quotes.   If the block is not in  use,
then the message (Block is not used) will be displayed.

The next line displays the position and size of the block in
the screen  file in  the format  [x,y]->[x+w,y+h] where  the
screen was originally saved from position (x,y) with a block
width and  height of  w and  h respectively.  The number  of
fields defined in the block follows next.

The rest of the line is concerned with internal information:
bsz is the size of the  current block, ofs is the offset  of
the block within the  screen file while fsz  is the size  of
the block used up by the screen, the difference between  bsz
and fsz being unused.  As an integrity check, the sum of the
current block's offset and block size should equal the  next
blocks offset.

The remaining lines  in a screen's  list display the  fields
defined in the screen.   Firstly, the type  of the field  is
listed, followed by a colon and the position and  dimensions
of the  field,  in the  format  of  (x,y) [w,h],  where  the
symbols have their usual meanings.

If the field is a menu field, then ScrList will move to  the
next  field   immediately.     Otherwise,   the   expression
associated with the field  is displayed, enclosed in  square
brackets.  Note that since  the screen file itself  contains
no variable  name information,  the  names of  variables  in
expressions cannot  be  determined  and they  are  therefore
displayed  as   variable  reference   numbers,   immediately


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preceded by a hash  # symbol.  If  you require a listing  of
the  expressions  attached  to   all  the  fields  in   your
application, then use the `Import/Save ASCII' option in  the
editor.  If the field  is a toggle list, then the  different
options in  the  list will  be  displayed on  the  following
lines, again enclosed in square brackets.

The following is  an extract from a  typical example of  the
output from ScrList showing all the salient features:

6:"Is Data ok?"
 [28,11]- [51,17] -   3  fields    (fsz:  221,  ofs:   2395,
bsz:221)
     Menu  : (24, 4) [21x 1] : [#1]
     MArea : (35,14) [ 7x 1]
     MArea : (35,15) [ 7x 1]
7:"Enter Names and Question 1"
 [ 0, 0]- [79,24] -  7 fields  (fsz:  901, ofs:  2616,  bsz:
901)
     Input : (24, 4) [21x 1] : [#2]
     Input : (24, 5) [ 9x 1] : [#3]
     Toggle: (24, 6) [15x 1] : [#4]
          [Civil Eng]
          [Science]
          [Electrical]
          [Mechanical]
          [Agriculture]
     Input : (24, 7) [11x 1] : [#5]
     Input : (18,13) [ 1x 1] : [#0[1,1]]
     Check : (18,14) [ 3x 1] : [#6]
     Radio : (18,15) [ 3x 4] : [#7]


6.6  ScrFix


ScrFix is  a command  line utility  which repairs  corrupted
screen files.   A screen file  can become  corrupted if  the
disk it resides on  generates read errors or  if the PC  was
switched off during a write to a screen file.

ScrFix can take either one  or two command line  paramaters.
The first paramater specifies the screen file to fix,  while
the second parameter specifies an optional output file.   If
the second  parameter  is  omitted,  the  original  file  is
renamed with  an  extension  of  ".bks"  and  the  corrected
version assumes the name of the older file.



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While  ScrFix  is  running,  it  displays  possible   screen
corruptions on  the monitor,  thus giving  warning of  those
screens which are most likely to be lost.

For  example,  if  a  screen  file  "test.scr"  has   become
corrupted,  it  could  be  fixed  using  the  following  two
commands:

            scrfix test

            scrfix test fixed

The first command  produces a corrected  output file  called
"test.scr", renaming  the corrupted  file "test.bks".    The
second line  creates  a  new corrected  screen  file  called
"fixed.scr" and does not alter the contents of the corrupted
file.

The best way to approach  fixing corrupted files is to  copy
the application  image file  (extension is  ".rxl") and  the
corrupted screen file  to some new  root name,  using a  DOS
command such as:

     copy broken.* test.*

where "broken" is the root name of the corrupted application
image and screen  file and "test"  is the  name of the  file
which will be modified by ScrFix.


6.7  ScrGrab


ScrGrab is a  terminate and stay  resident utility which  is
used to grab text screens from the monitor and to place  the
contents in files compatible with RExL's ".SCR" format.  The
ScrAdd utility can be used to combine screen files together.
Typical applications of ScrGrab and ScrAdd are demonstration
programs like that supplied with RExL, bug reports  supplied
with screen dumps and so on.

When loaded in  memory, ScrGrab  uses about  2,500 bytes  of
memory.   When it  is  no longer  required,  it and  can  be
unloaded from memory from the command line.

The  command  line  arguments  which  ScrGrab  uses  are  as
follows:



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       -h and -? Show command line help

       -u        Unload  from  memory.    If  further   T&SR
       programs have  been  loaded  since ScrGrab,  then  it
       cannot be unloaded since  doing so would corrupt  DOS
       and most likely crash the machine.

       -k....:   This  option  is   used  to   set  up   the
       keystroke,  by  default  <Alt-G>,  which  will  cause
       ScrGrab to save a screen to disk.  Unless you have  a
       keyboard scan  code table,  you'll need  to used  the
       KbdScan utility to determine the exact four character
       keyboard scan  code to  supply here.   Refer  to  the
       section on Scan for more information.

       -d:       Requests  ScrGrab  to  report  the  current
       defaults which it is using. The first line gives  the
       activating scan code, in a format compatible with the
       output from KbdScan while the next line gives the DOS
       paragraph  where  the  program   is  loaded.     This
       information is purely  technical and is  not of  much
       use.

You  should  not  run  any  T&SR  programs  from  within  an
operating system shell, such as when the `File/OS shell'  is
selected from the editor, since T&SR's perform surgery  upon
DOS  which  will  cause  it   to  crash  if  the  shell   is
subsequently terminated using the DOS exit command.


6.8  ScrXtrct


ScrXtrct is a utility which  can extract and place a  screen
from one screen file into another screen file.  The  general
command line format of this command are:

              ScrXtrct OldScr ScreenNo NewScr

where OldScr is  the screen  file from  which screen  number
ScreenNo will be extracted and placed into the NewScr screen
file, erasing NewScr if it already exists.  Unlike the  rest
of RExL,  ScreenNo  is  one-based, meaning  that  the  first
screen is  number 1,  the second  number 2  and so  on.   If
OldScr contains a number of screens and you are not sure  of
the reference number  of the screen you  want, then you  can
use the ScrList utility to list them along with their screen
numbers.


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6.9  ScrAdd


ScrAdd is a  utility which can  extract and  place a  screen
from one screen file into another screen file.  The  general
command line format of this command are:

               ScrAdd OldScr ScreenNo NewScr

where OldScr is  the screen  file from  which screen  number
ScreenNo will be extracted and placed into the NewScr screen
file.  Note that, as  with ScrXtrct, ScreenNo is  one-based.
If OldScr contains a number of screens, then you can use the
ScrList  utility  to  list  them  along  with  their  screen
numbers.

If the name of the screen specified clashes with one in  the
new screen file,  then you will  be promted  to enter a  new
name for the screen being added.

ScrAdd does not perform  any of the optimization  operations
carried out in  the editor upon screen  files when they  are
being modified.   Instead, it simply  appends the screen  to
NewScr.

ScrAdd is  generally used  in combination  with ScrGrab  and
ScrXtrct to move screens from one screen file to the next.


6.10  MI


MI,  short  for   memory  information,  displays   pertinent
information about the state of DOS and the programs resident
in your  PC.   The following  is  a typical  display of  the
output from MI:


MI  Version 2.1  Copyright (c) 1992, The Software Loft
-------- -------- ------------ --------------
PSP addr Size     Owner        Hooked vectors
-------- -------- ------------ --------------
0008     24,048   [  Dos  ]
084E     2,368    [ Shell ]    22 23 24 2E EF
         64       [ Free  ]
084E     752      [ Shell ]
0AA6     128      [  Dos  ]
0921     6,208    edos.com     2F


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0AA6     2,592    edos.com
0B54     2,320    scrgrab.com  09 16 21 28
0BE7     606,768  [ Free  ]
------------  ----------------------  ----------------------
Memory        Total bytes             Available bytes
------------  ----------------------  ----------------------
Conventional  655,360     (640k)      606,592     (592k)
Expanded      EMS not responding
Extended      3,145,728   (3,072k)    0           (0k)
XMS           2,048,000   (2,000k)    2,048,000   (2,000k)
HMA allocated, EBDA not present
There are  12,102,400 (out  of  120,946,944) bytes  free  on
drive N:


The first  section of  the display  gives information  about
memory control blocks (MCB's) in  low DOS memory, between  0
and 640k.  It lists the hexadecimal address of the owner  of
the MCB in `PSP addr' column, the amount of memory owned  by
the block  in the  `Size' column,  the name  of the  program
which owns the PSP in the `Owner' column.  The final  column
lists, in  hexadecimal,  the  interrupt  vectors  which  are
hooked into  the memory  controlled by  the MCB.   From  the
above display, we  can see that ScrGrab  hooks the high  and
low  priority  keyboard  interrupts,  the  main  DOS  server
interrupt  and  the  DOSok  interrupt.    A  DOS   technical
reference will  tell  you  the  meanings  and  uses  of  the
different interrupt numbers.

DOS  itself  also  owns  blocks  of  memory  and  these  are
signalled by  owners of  `[Dos]',  for blocks  with  invalid
environments and  `[Shell]', for  blocks which  do not  have
program names attached to them.

The second section  of the output from  MI lists the  amount
memory available  in each  of the  different memory  schemes
used in the  PC. The listing is  divided into five  columns:
The first gives the type  of memory about to be listed,  the
second gives the total amount of memory allocatable and  the
fourth gives the amout of memory remaining unallocated.  The
third  and  fifth  columns   convert  the  byte  counts   to
measurements in kilobytes (bytes divided by 1024).

Conventional memory  extends  from  0 to  640k,  unless  VGA
graphics memory  has  been  used to  backfill  DOS  to  736k
(generally, it isn't).   The  available conventional  figure
will always be  slightly less than that  noted as [Free]  in
the first section of the listing.  This is because the first


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section lists as free the memory used by the environment  of
the currently active program, while the second does not.

The next line gives the amount of expanded memory (LIM  EMS)
in your system.  It interrogates the status of int 67h which
controls the interface  to the memory.   If  this vector  is
NULL, then the  message `None' will  be displayed.   If  the
vector exists, but  does not respond in  the way it  should,
then the message `EMS not responding' will be displayed.

The third line in this  section gives the amount of  vanilla
extended memory available and free.  The total is read  from
the CMOS setup information in  your PC, while the amount  of
free memory is taken from int 15h/fn 88h.  The final line in
the memory display gives the amount of XMS (Extended  Memory
System) in your machine.

The second last line  gives the on/off status  of the DOS  5
HMA (High Memory Arena) and that of the EBDA (Extended  BIOS
Data Area) which is normally  only present on PS/2,  Compaq,
Digital and Olivetti PC's.

The final line gives the  total disk space and the space  on
the currently selected  disk drive.   MI  can optionally  be
followed by  a  drive  letter  to  specify  a  drive,  whose
statistics are displayed instead of the current drive.   For
example the line MI  a: will list the  free space and  total
drive space on the A: drive rather than the current drive.

MI takes one of two optional command line parameters, -c and
-m.

The -c parameter instructs MI  to display the CPU type,  the
floating point coprocessor type, the video adapter type.  If
the  processor is  an Intel 80386 or  above, then a  message
will be  displayed saying whether or not the CPU is  running
in protected mode.

The  -m  parameter  causes  the  normal  `condensed'  memory
control block  display  to be  displayed  in its  low  level
unprocessed  form.  When  -m  is  specified,  no  memory  or
capacities are determined.








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6.11  KbdSpeed


KbdSpeed is a small utility to set the keyboard repeat  rate
on AT class computers with  extended keyboards.  The  format
of the command is as follows:

                  KbdSpeed <letter><digit>

where letter  is  a  letter in  the  range  `a' to  `z'  and
controls the repeat rate, with `a' at 30 repeats per  second
and `z' meaning 5  repeats per second. digit  is a digit  in
the range `1' to `4'  specifying the delay before  repeating
occurs.   1  specifies  a delay  of  1/4  seconds, up  to  4
specifying a delay of 1 second.

To set the keyboard to  repeat at 30 characters per  second,
with a delay of 1/4  seconds before auto repeat occurs,  the
following command would be issued:

                        KbdSpeed a1

If you run KbsSpeed from within MicroSoft Windows, then  the
program will have no effect, since Windows resets the  rates
of its own accord, ignoring any preset values.

KbdSpeed is most useful in RExL when designing screens where
the cursor  may  need to  make  large movements  around  the
screen.  The normal repeat rate of 10 characters per  second
then becomes an irritation.


6.12  KbdScan


KbdScan is another small utility which reads from keystrokes
from the keyboard and displays  the keyboard scan code,  the
BIOS keystroke return  value and the TSR  hotkey code.   The
information is displayed on three sucessive lines.

The format of the command is as follows:

                        KbdScan [-x]

This utility  is provided  so that  the activating  keyboard
scan code for  ScrGrab can be  changed.  If  you want to  do
this, take the TSR hotkey  code displayed on the final  line



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  - Appendices.                         Page: 135 -


of display and place it  as the parameter to the -k  command
line option to ScrGrab.

The following is  output from KbdScan,  with <Alt-0> as  the
last key pressed:

KbdScan  Version 2.1  (C) Copyright 1992, The Software Loft
Press any key, ESC (twice) aborts :
Shift/scan code   :088b
BIOS return value :8100
TSR hotkey code   :0881

To change the  activating keystroke in  ScrGrab to  <Alt-0>,
the following command would be issued.

                       ScrGrab -k0881

Finally, ScrGrab accepts  the command line  option `-x'.  If
this option is included,  ScrGrab will read keystrokes  from
an extended 101-102 key keyboard.  This is only supplied  as
an extra feature, and is not used in RExL.





























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  - Appendices.                         Page: 136 -




















































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                         Chapter 7

                         Afterword


This appendix  gives a  few pointers  to the  directions  in
which the Software Loft hopes  to go when developing  future
versions of RExL.   Any suggestions  for features which  you
would like  to  see  incorporated  would  be  most  welcome.
Please  remember  that  without  your  support,  we   cannot
continue to  supply you  with  low cost,  quality  software.
Thank you.

    o  More features in the debugger:  Break on  expression,
       pass count  breakpoints,  break on  variable  access.
       VGA 43 and 50 line mode support.

    o  More features  in  the  editor: Search  and  replace,
       lines  longer  than   65  characters,  and   function
       references (similar to  variable references).   Color
       installation program  to  set  up  colors  of  menus,
       windows and various other  system parameters. VGA  43
       and 50 line mode support.

    o  Language: rules attached to variables.  Every time  a
       variable is either accessed  or changed, its rule  is
       called.  User defined RExL  functions.  Link in  with
       C, assembly language and Pascal.

    o  New features  in the  screen  designer.   These  will
       include pictures for  input and output  (as in  dBase
       compatible languages) as well as undo.

    o  Improve the  speed  of the  runtime-debugger  module.
       Currently, we  have  a  better  expression  evaluator
       undergoing tests and  we hope  to include  it in  the
       next major release.

    o  Mouse handling.





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  - Appendices.                         Page: 138 -


    o  Add  true  relational  capability  to  the   database
       module.  Most  of the code required  is in place  for
       this.

    o  A portable runtime module to allow the programmer  to
       write applications in  DOS and to  port the  finished
       product to  Unix,  and  other  text  based  operating
       systems.

    o  A windows version  of RExL.   The current version  of
       RExL has taken fourteen months  for us to write.   We
       hope to be able to  port most of the code to  Windows
       easily enough  and  to  have an  alpha  test  version
       running sometime around December of 1992.




































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