Atari Mega Archive 1/Atari Mega Archive - Volume 1.iso/language/prlogtxt.arc/README.DOC

Text File | 1988-07-24 | 8KB | 181 lines

                 TOY Prolog ST - English edition
                 -------------------------------

Contents of disk
----------------
     TOY.PRG      )      The TOY Prolog interpreter
     SYSFILE.TOY  )

     PROLOG.DOC          53-page manual, translated from German

     README.DOC          The file you are reading

     BOOTER.TOY   )      Auxiliary programs in
     EDITOR.TOY   )        intermediate code - see
     CALLTREE.TOY )        section 4 of manual

     TICTAC.TOY          Noughts & crosses demo (intermediate
                           code) (manual, p.42)

  \SOURCE\ folder: programs in Prolog (in English originally):

     MONITOR.PRO         Source code for user interface (p.47)

     EDITOR       )      Source code for auxiliary programs
     CALLTREE     )        (pp.38-39)

     ALPHA        )
     TOYSEQ       )      Demonstration programs (pp.40-42)
     TICTAC.TOE   )

  \DEMOS\ folder: more Prolog programs (translated from German):

     TOYDEMOS            graphics demo, access to disk directory,
                           + a simple recursive tab function
     FAMILY              logic of family relationships
     COLOURS             colouring a map with 4 colours
     QUIKSORT            sorting lists

Introduction
------------
Welcome to Prolog - PROgramming in LOGic - the 'fifth generation'
language  currently replacing LISP as the language of choice  for
artificial intelligence programming. A few lines of Prolog can do
things  that would take pages of code in a conventional  language
like  Pascal,  C or BASIC.  But as it is fundamentally  different
from  sequential/algorithmic languages like these (and also  from
other,  less conventional computer languages),  you have a  whole
set of new concepts to learn before you can make much use of  its
power. It is not just the jargon that's weird and unfamiliar, but
the  whole  philosophy  of programming  that  Prolog  terminology
describes.

     Let's face it, it takes a book to explain what Prolog is all
about. The manual describes this particular implementation pretty
thoroughly,  but it does not set out to be an introductory text -
it  assumes  you  already  know  what  words  like  'arity'   and
'principal functor' mean.  So if you do want to learn Prolog  you
will have to get a book about it. The standard text is the one by
Clocksin  &  Mellish,  mentioned  in  the  manual.  A  short  and
comparatively cheap book that I am finding quite helpful,  though
it  does  not  cover  everything  in  TOY  Prolog,  is  J.Doores,
A.R.Reiblein & S.Vadera: Prolog - Programming for Tomorrow. Sigma
Press, Wilmslow, Cheshire, 1987. £10-95.

     If you do not have a textbook to refer to yet,  just in case
reading the manual still leaves you wondering where to start, the
following notes may help you get going with this package.

Using TOY Prolog
----------------
Run  TOY.PRG from the desktop,  with SYSFILE.TOY present  on  the
same  directory.  You should eventually get a message saying  the
program is listening and a prompt,
     ?-
followed  by a blinking cursor.  Now you are supposed to enter  a
valid Prolog clause,  terminated by a full stop. This sets Prolog
a goal, which it will attempt to satisfy. In some cases, a lot of
printout  can be generated on the way,  but eventually  the  goal
will  either succeed or fail,  and Prolog will respond  'yes'  or
'no' respectively, and give you another '?-' prompt.

     E.g.  you can set Prolog problems in simple arithmetic  such
as
     ?- sum(27,34,X).
or
     ?- sum(X,3,-11).
Here  X,  being a sequence of alphanumeric  characters  beginning
with a capital letter,  is interpreted as a variable,  and Prolog
will give it a value.  To get a new prompt,  type a full stop and
Return. Or you can ask
     ?- 32*48 > 1024/3.
or
     ?- 'neil' @< 'margaret'.
and just get 'yes' or 'no'.

To quit TOY Prolog, just type
        stop.

Loading a program
-----------------
In principle,  you can enter complicated predicates directly like
this, but it is not very convenient. For one thing, if you make a
mistake  you have to type the whole line again.  It is  generally
easier to create a Prolog program outside the interpreter,  using
your favourite programming editor,  and load it in from disk when
Prolog  is running.  Once loaded,  it can be modified  using  the
editor provided.

     There are two ways of loading programs.  A program in Prolog
source code is loaded with 'consult'.  E.g.  to load the  example
program FAMILY from drive B you enter
     ?- consult('b:\demos\family').
whereupon Prolog will read it in,  echoing it all to the  screen,
stopping to execute commands (beginning with ':-') when it  comes
to them, until it comes to the 'end.'. At that point the goal has
been satisfied, so Prolog prints 'yes' and returns control to the
keyboard.

     This is very slow,  so another method is also provided. Once
your  program  is  fully debugged,  you  can  translate  it  into
intermediate code as described in the manual, generating a '.TOY'
file,  which can then be loaded very quickly with 'sysload'. E.g.
to load the editor you enter
     ?- sysload('b:\editor.toy').

     Once a program has been loaded,  the information it contains
remains in Prolog's built-in database. You can call predicates in
it, and ask questions using the facts and rules it contains. E.g.
after loading FAMILY, you can enter
     ?- parent(X, jesus).
and Prolog will answer
     X is joseph
leaving the cursor on the same line. If you type a semicolon (and
Return), it will resatisfy this goal with another solution,
     X is mary
This time,  attempting to resatisfy the goal fails,  there are no
more solutions.

There is plenty of study material in the example programs, and it
is worth printing listings of them as well as of the manual.

This translation
----------------
TOY  Prolog  was written in Warsaw and published in  an  English-
language  book,  which  unfortunately  I have not  been  able  to
obtain. This Atari ST version was created in Germany and released
as  a  public  domain package  with  German  documentation.  This
English  version  of the package is the same except that  I  have
translated  the documentation into English and edited it  into  a
single  document,  adding  a  fuller table of  contents  and  two
indexes  (one  of  the GEM functions by  their  standard  names);
translated the comments in the example programs;  and added  this
README file. One or two little mistakes I happened to spot in the
German documentation have been corrected,  but I cannot guarantee
the rest is perfect!  Once upon a time,  the German documentation
appears  to have been in FirstWord format,  with some  names  and
symbols distinguished by bold type. By the time it reached me, it
was  in ASCII and this distinction had been lost - sorry if  this
adds any confusion.  Being a beginner in Prolog, not particularly
familiar  with German,  and without access to the original source
book,  I can hardly have avoided an occasional slip or  deviation
from  the  norms  of TOY Prolog  terminology,  however  it  seems
preferable to release the translation in its present form  rather
than  sitting on it just because I might be able to do it  better
with another year's experience.

     Though  my contribution is small compared with that  of  the
professionals who wrote the program,  still translating over 100k
of  files as technical as this is by no means a negligible  task,
in  fact it amounted to several weeks' work all told.  And  while
they were no doubt paid for their work,  I don't get a penny  for
mine.  So if you would like to encourage me to help make more  of
the  excellent PD software that comes from Germany  available  in
English via the ST Club, why not send me a donation?

                                   Martin Willson,
                                     1 Bincleaves Road,
                                       Wey