TeX 1995 July/TeX CD-ROM July 1995 (Disc 1)(Walnut Creek)(1995).ISO/macros/plain/contrib/literate/makeprog.web

Text File | 1989-11-22 | 35.0 KB | 1,056 lines

@                                                           % sect.    2
The program begins with a fairly normal header, made up of
pieces that will mostly be filled in later.  The input comes
from files |doc_file| and |change_file|, the output goes to
file |prog_file|.  Messages from \MAKEPROG{} are written to
|term_out|, which is supposed to be the terminal.
@^system dependencies@>

If it is necessary to abort the job because of a fatal
error, the program calls the `|jump_out|' procedure, which
goes to the label |end_of_MAKEPROG|.

@d end_of_MAKEPROG = 9999 {go here to wrap it up}

@p @t\4@>@<Compiler directives@>@/
program MAKEPROG(@!doc_file,@!change_file,@!prog_file);
label end_of_MAKEPROG; {go here to finish}
const @<Constants in the outer block@>@;
type @<Types in the outer block@>@;
var @<Globals in the outer block@>@;
@t\4@>@<Error handling procedures@>@;
procedure initialize;
  var @<Local variables for initialization@>@;
  begin @<Set initial values@>
  end;


@                                                           % sect.    3
Some of this code is optional for use when debugging only;
such material is enclosed between the delimiters \&{debug}
and \&{gubed}.

@d debug==@{ {change this to `$\\{debug}\equiv\null$' when debugging}
@d gubed==@t@>@} {change this to `$\\{gubed}\equiv\null$' when debugging}
@f debug==repeat
@f gubed==until


@                                                           % sect.    4
The \PASCAL\ compiler used to develop this system has
``compiler directives'' that can appear in comments whose
first character is a dollar sign.  In production versions of
\MAKEPROG{} these directives tell the compiler that it is
safe to avoid range checks and to leave out the extra code
it inserts for the \PASCAL\ debugger's benefit.
@^system dependencies@>

@<Compiler directives@>=
@{@&@=$D-@> @} {no debug overhead}
@!debug @{@&@=$D+@> @}@+ gubed @; {but turn everything on when debugging}


@                                                           % sect.    5
Labels are given symbolic names by the following
definitions.  We insert the label `|exit|' just before the
`\&{end}' of a procedure in which we have used the
`|return|' statement defined below; the label `|restart|' is
occasionally used at the very beginning of a procedure; and
the label `|reswitch|' is occasionally used just prior to a
\&{case} statement in which some cases change the conditions
and we wish to branch to the newly applicable case.  Loops
that are set up with the \&{loop} construction defined below
are commonly exited by going to `|done|' or to `|found|' or
to `|not_found|', and they are sometimes repeated by going
to `|continue|'.

@d exit=10 {go here to leave a procedure}
@d restart=20 {go here to start a procedure again}
@d reswitch=21 {go here to start a case statement again}
@d continue=22 {go here to resume a loop}
@d done=30 {go here to exit a loop}
@d found=31 {go here when you've found it}
@d not_found=32 {go here when you've found something else}


@                                                           % sect.    6
Here are some macros for common programming idioms.

@d incr(#) == #:=#+1 {increase a variable by unity}
@d decr(#) == #:=#-1 {decrease a variable by unity}
@d loop == @+ while true do@+ {repeat over and over until a |goto| happens}
@d do_nothing == {empty statement}
@d return == goto exit {terminate a procedure call}
@f return == nil
@f loop == xclause


@                                                           % sect.    7
We assume that |case| statements may include a default case
that applies if no matching label is found.  Thus, we shall
use constructions like
@^system dependencies@>
$$
\vbox{\halign{#\hfil\cr
|case x of|\cr
   \quad 1: $\langle\,$code for $x=1\,\rangle$;\cr
   \quad 3: $\langle\,$code for $x=3\,\rangle$;\cr
   \quad |othercases| $\langle\,$code for |x<>1| and |x<>3|$\,\rangle$\cr
|endcases|\cr
}}
$$
since most \PASCAL\ compilers have plugged this hole in the
language by incorporating some sort of default mechanism.
For example, the compiler used to develop \.{WEB} and \TeX\
allows `|others|:' as a default label, and other \PASCAL s
allow syntaxes like `\&{else}' or `\&{otherwise}' or
`\\{otherwise}:', etc.  The definitions of |othercases| and
|endcases| should be changed to agree with local
conventions.  (Of course, if no default mechanism is
available, the |case| statements of this program must be
extended by listing all remaining cases.)

@d othercases == others: {default for cases not listed explicitly}
@d endcases == @+end {follows the default case in an extended |case| statement}
@f othercases == else
@f endcases == end


@                                                           % sect.    8
The following parameter is set big enough to be sufficient
for most applications of \MAKEPROG{}.

@<Constants...@>=
@!buf_size=500; {maximum length of input line}


@                                                           % sect.    9
A global variable called |history| will contain one of four values
at the end of every run: |spotless| means that no unusual messages were
printed; |harmless_message| means that a message of possible interest
was printed but no serious errors were detected; |error_message| means that
at least one error was found; |fatal_message| means that the program
terminated abnormally. The value of |history| does not influence the
behavior of the program; it is simply computed for the convenience
of systems that might want to use such information.

@d spotless=0 {|history| value for normal jobs}
@d harmless_message=1 {|history| value when non-serious info was printed}
@d error_message=2 {|history| value when an error was noted}
@d fatal_message=3 {|history| value when we had to stop prematurely}
@#
@d mark_harmless==@t@>@+if history=spotless then history:=harmless_message
@d mark_error==history:=error_message
@d mark_fatal==history:=fatal_message

@<Glob...@>=@!history:spotless..fatal_message; {how bad was this run?}

@                                                           % sect.   10
@<Set init...@>=history:=spotless;





@* The character set.                                       % sect.   11

\noindent One of the main goals in the design of \MAKEPROG{}
has been to make it readily portable between a wide variety
of computers.  Yet \MAKEPROG{} by its very nature must use a
greater variety of characters than most computer programs
deal with, and character encoding is one of the areas in
which existing machines differ most widely from each other.

To resolve this problem, all input to \MAKEPROG{} is
converted to an internal seven-bit code that is essentially
standard \ASCII{}, the ``American Standard Code for
Information Interchange.'' The conversion is done
immediately when each character is read in.  Conversely,
characters are converted from \ASCII{} to the user's
external representation just before they are output.  Such
an internal code is never relevant to users of \MAKEPROG{}.

\noindent Here is a table of the standard visible \ASCII{} codes:
$$\def\:{\char\count255\global\advance\count255 by 1}
\count255='40
\vbox{
\hbox{\hbox to 40pt{\it\hfill0\/\hfill}%
\hbox to 40pt{\it\hfill1\/\hfill}%
\hbox to 40pt{\it\hfill2\/\hfill}%
\hbox to 40pt{\it\hfill3\/\hfill}%
\hbox to 40pt{\it\hfill4\/\hfill}%
\hbox to 40pt{\it\hfill5\/\hfill}%
\hbox to 40pt{\it\hfill6\/\hfill}%
\hbox to 40pt{\it\hfill7\/\hfill}}
\vskip 4pt
\hrule
\def\^{\vrule height 10.5pt depth 4.5pt}
\halign{\hbox to 0pt{\hskip -24pt\O{#0}\hfill}&\^
\hbox to 40pt{\tt\hfill#\hfill\^}&
&\hbox to 40pt{\tt\hfill#\hfill\^}\cr
04&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
05&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
06&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
07&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
10&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
11&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
12&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
13&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
14&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
15&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
16&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
17&\:&\:&\:&\:&\:&\:&\:\cr}
\hrule width 280pt}$$
(Actually, of course, code @"20 is an invisible blank
space.) Code @"3E was once an upward arrow (\.{\char'13}),
and code @"3F was once a left arrow (\.^^X), in olden times
when the first draft of \ASCII{} code was prepared; but
\MAKEPROG{} works with today's standard \ASCII{} in which
those codes represent circumflex and underline as shown.

@<Types...@>=
@!ASCII_code=0..@"7F; {seven-bit numbers, a subrange of the integers}


@                                                           % sect.   12
The original \PASCAL\ compiler was designed in the late 60s,
when six-bit character sets were common, so it did not make
provision for lowercase letters.  Nowadays, of course, we
need to deal with both capital and small letters in a
convenient way, so \MAKEPROG{} assumes that it is being used
with a \PASCAL\ whose character set contains at least the
characters of standard \ASCII{} as listed above.  Some
\PASCAL\ compilers use the original name |char| for the data
type associated with the characters in text files, while
other \PASCAL s consider |char| to be a 64-element subrange
of a larger data type that has some other name.

In order to accommodate this difference, we shall use the
name |text_char| to stand for the data type of the
characters in the input and output files.  We shall also
assume that |text_char| consists of the elements
|chr(first_text_char)| through |chr(last_text_char)|,
inclusive.  The following definitions should be adjusted if
necessary.
@^system dependencies@>

@d text_char == char {the data type of characters in text files}
@d first_text_char=0 {ordinal number of the smallest element of |text_char|}
@d last_text_char=127 {ordinal number of the largest element of |text_char|}

@<Types...@>=
@!text_file=packed file of text_char;


@                                                           % sect.   13
The \MAKEPROG{} processor convert between \ASCII{} code and
the user's external character set by means of arrays |xord|
and |xchr| that are analogous to \PASCAL's |ord| and |chr|
functions.

@<Globals...@>=
@!xord: array [text_char] of ASCII_code;
  {specifies conversion of input characters}
@!xchr: array [ASCII_code] of text_char;
  {specifies conversion of output characters}


@                                                           % sect.   14
If we assume that every system using \.{WEB} is able to read
and write the visible characters of standard \ASCII{}
(although not necessarily using the \ASCII{} codes to
represent them), the following assignment statements
initialize most of the |xchr| array properly, without
needing any system-dependent changes.  For example, the
statement \.{xchr["A"]:=\'A\'} that appears in the present
\.{WEB} file might be encoded in, say, \hbox{\mc EBCDIC}
code on the external medium on which it resides, but
\.{TANGLE} will convert from this external code to \ASCII{}
and back again.  Therefore the assignment statement
\.{XCHR[65]:=\'A\'} will appear in the corresponding
\PASCAL\ file, and \PASCAL\ will compile this statement so
that |xchr[65]| receives the character \.A in the external
(|char|) code.  Note that it would be quite incorrect to say
\.{xchr["A"]:="A"}, because |"A"| is a constant of type
|integer|, not |char|, and because we have $|"A"|=65$
regardless of the external character set.

@<Set init...@>=
xchr[" "]:=' ';
xchr["!"]:='!';
xchr[""""]:='"';
xchr["#"]:='#';
xchr["$"]:='$';
xchr["%"]:='%';
xchr["&"]:='&';
xchr["'"]:='''';@/
xchr["("]:='(';
xchr[")"]:=')';
xchr["*"]:='*';
xchr["+"]:='+';
xchr[","]:=',';
xchr["-"]:='-';
xchr["."]:='.';
xchr["/"]:='/';@/
xchr["0"]:='0';
xchr["1"]:='1';
xchr["2"]:='2';
xchr["3"]:='3';
xchr["4"]:='4';
xchr["5"]:='5';
xchr["6"]:='6';
xchr["7"]:='7';@/
xchr["8"]:='8';
xchr["9"]:='9';
xchr[":"]:=':';
xchr[";"]:=';';
xchr["<"]:='<';
xchr["="]:='=';
xchr[">"]:='>';
xchr["?"]:='?';@/
xchr["@@"]:='@@';
xchr["A"]:='A';
xchr["B"]:='B';
xchr["C"]:='C';
xchr["D"]:='D';
xchr["E"]:='E';
xchr["F"]:='F';
xchr["G"]:='G';@/
xchr["H"]:='H';
xchr["I"]:='I';
xchr["J"]:='J';
xchr["K"]:='K';
xchr["L"]:='L';
xchr["M"]:='M';
xchr["N"]:='N';
xchr["O"]:='O';@/
xchr["P"]:='P';
xchr["Q"]:='Q';
xchr["R"]:='R';
xchr["S"]:='S';
xchr["T"]:='T';
xchr["U"]:='U';
xchr["V"]:='V';
xchr["W"]:='W';@/
xchr["X"]:='X';
xchr["Y"]:='Y';
xchr["Z"]:='Z';
xchr["["]:='[';
xchr["\"]:='\';
xchr["]"]:=']';
xchr["^"]:='^';
xchr["_"]:='_';@/
xchr["`"]:='`';
xchr["a"]:='a';
xchr["b"]:='b';
xchr["c"]:='c';
xchr["d"]:='d';
xchr["e"]:='e';
xchr["f"]:='f';
xchr["g"]:='g';@/
xchr["h"]:='h';
xchr["i"]:='i';
xchr["j"]:='j';
xchr["k"]:='k';
xchr["l"]:='l';
xchr["m"]:='m';
xchr["n"]:='n';
xchr["o"]:='o';@/
xchr["p"]:='p';
xchr["q"]:='q';
xchr["r"]:='r';
xchr["s"]:='s';
xchr["t"]:='t';
xchr["u"]:='u';
xchr["v"]:='v';
xchr["w"]:='w';@/
xchr["x"]:='x';
xchr["y"]:='y';
xchr["z"]:='z';
xchr["{"]:='{';
xchr["|"]:='|';
xchr["}"]:='}';
xchr["~"]:='~';@/
xchr[0]:=' '; xchr[@"7F]:=' '; {these \ASCII{} codes are not used}


@                                                           % sect.   15
Some of the nonprintable \ASCII{} codes have been given
symbolic names in \MAKEPROG{} because they are used with a
special meaning.

@d tab_mark=@"09              {\ASCII{} code used as tab-skip}
@d line_feed=@"0A             {\ASCII{} code thrown away at end of line}
@d form_feed=@"0C             {\ASCII{} code used at end of page}
@d carriage_return=@"0D       {\ASCII{} code used at end of line}


@                                                           % sect.   16
When we initialize the |xord| array and the remaining parts of |xchr|,
it will be convenient to make use of an index variable, |i|.

@<Local variables for init...@>=
@!i:0..last_text_char;


@                                                           % sect.   17
Here now is the system-dependent part of the character set.
If \MAKEPROG{} is being implemented on a garden-variety
\PASCAL\ for which only standard \ASCII{} codes will appear
in the input and output files, you don't need to make any
changes here.
@^system dependencies@>

Changes to the present module will make \MAKEPROG{} more
friendly on computers that have an extended character set,
so that one can type things like Umlaute.  If you have an
extended set of characters that are easily incorporated into
text files, you can assign codes arbitrarily here, giving an
|xchr| equivalent to whatever characters the users of
\MAKEPROG{} are allowed to have in their input files,
provided that unsuitable characters do not correspond to
special codes like |carriage_return| that are listed above.

@<Set init...@>=
for i:=1 to " "-1 do xchr[i]:=' ';


@                                                           % sect.   18
The following system-independent code makes the |xord| array
contain a suitable inverse to the information in |xchr|.

@<Set init...@>=
for i:=first_text_char to last_text_char do xord[chr(i)]:=" ";
for i:=1 to "~" do xord[xchr[i]]:=i;





@* Basic Input and output.

\noindent The input conventions of \MAKEPROG{} are identical
to those of \.{WEB}.  Therefore people who need to make
modifications to both systems should be able to do so
without too many headaches.


@                                                           % sect.   20
Terminal output is done by writing on file |term_out|, which
is assumed to consist of characters of type |text_char|:
@^system dependencies@>

@d print(#)==write(term_out,#) {`|print|' means write on the terminal}
@d print_ln(#)==write_ln(term_out,#) {`|print|' and then start new line}
@d new_line==write_ln(term_out) {start new line}
@d print_nl(#)==  {print information starting on a new line}
  begin new_line; print(#);
  end

@<Globals...@>=
@!term_out:text_file; {the terminal as an output file}


@                                                           % sect.   21
Different systems have different ways of specifying that the
output on a certain file will appear on the user's terminal.
Here is one way to do this on the \PASCAL{} system that was
used in \.{TANGLE}'s initial development.
@^system dependencies@>

@<Set init...@>=
rewrite(term_out,'TTY:'); {send |term_out| output to the terminal}


@                                                           % sect.   22
The |update_terminal| procedure is called when we want to
make sure that everything we have output to the terminal so
far has actually left the computer's internal buffers and
been sent.
@^system dependencies@>

@d update_terminal == break(term_out) {empty the terminal output buffer}


@                                                           % sect.   23
The main input comes from |doc_file|; this input may be
overridden by changes in |change_file|.  (If |change_file|
is empty, there are no changes.)

@<Globals...@>=
@!doc_file:text_file; {primary input}
@!change_file:text_file; {updates}


@                                                           % sect.   24
The following code opens the input files.  Since these files
were listed in the program header, we assume that the
\PASCAL\ runtime system has already checked that suitable
file names have been given; therefore no additional error
checking needs to be done.
@^system dependencies@>

@< Set init... @>=
reset(doc_file); reset(change_file);


@                                                           % sect.   25
The output goes to |prog_file|.

@<Globals...@>=
@!prog_file: text_file;


@                                                           % sect.   26
The following code opens |prog_file|.  Since this file is
listed in the program header, we assume that the \PASCAL\
runtime system has checked that a suitable external file
name have been given.
@^system dependencies@>

@<Set init...@>=
rewrite(prog_file);


@                                                           % sect.   27
Input goes into an array called |buffer|.

@<Globals...@>=
@!buffer: array[0..buf_size] of ASCII_code;


@                                                           % sect.   28
The |input_ln| procedure brings the next line of input from
the specified file into the |buffer| array and returns the
value |true|, unless the file has already been entirely
read, in which case it returns |false|.  The conventions of
\.{WEB} are followed; i.e., |ASCII_code| numbers
representing the next line of the file are input into
|buffer[0]|, |buffer[1]|, \dots, |buffer[limit-1]|; trailing
blanks are ignored; and the global variable |limit| is set
to the length of the line.  The value of |limit| must be
strictly less than |buf_size|.
@^system dependencies@>

We assume that none of the |ASCII_code| values of
|buffer[j]| for |0<=j<limit| is equal to 0, @"7F,
|line_feed|, |form_feed|, or |carriage_return|.

@p
function input_ln(var f:text_file):boolean; {inputs a line or returns |false|}
   var final_limit:0..buf_size; {|limit| without trailing blanks}
   begin limit:=0; final_limit:=0;
   if eof(f) then input_ln:=false
   else  begin
      while not eoln(f) do
         begin buffer[limit]:=xord[f^]; get(f);
         incr(limit);
         if (buffer[limit-1]<>" ") and (buffer[limit-1]<>tab_mark) then
            final_limit:=limit;
         if limit=buf_size then
            begin while not eoln(f) do get(f);
            decr(limit); {keep |buffer[buf_size]| empty}
            print_nl('! Input line too long'); error; mark_error;
@.Input line too long@>
            end;
         end;
      read_ln(f); limit:=final_limit; input_ln:=true;
      end;
   end;





@* Reporting errors to the user.                            % sect.   29

\noindent Errors are reported to the user by saying
$$
   \hbox{`|err_print('! Error message')|'},
$$
followed by `|jump_out|' if no recovery from the error is
provided.  This will print the error message followed by an
indication of where the error was spotted in the source
file.  Note that no period follows the error message, since
the error routine will automatically supply a period.

\noindent The actual error indications are provided by a
procedure called |error|.

@d err_print(#)==begin print_nl(#); error; mark_error; end

@<Error handling...@>=
procedure error; {prints '\..' and location of error message}
   begin @< Print error location @>;
   update_terminal;
   end;


@                                                           % sect.   32
The error locations can be indicated by using the global
variables |line| and |changing|, which tell respectively the
the current line number and whether or not the current line
is from |change_file| or |doc_file|.  This routine should be
modified on systems whose standard text editor has special
line-numbering conventions.
@^system dependencies@>

@< Print error location @>=
begin
if changing then  print('. (change file ') @+ else print('. (');
print_ln('l.', line:1, ')');
print(' '); {this space separates the message from future output}
end


@                                                           % sect.   34
The |jump_out| procedure just cuts across all active
procedure levels and jumps out of the program.  This is the
only non-local |goto| statement in \MAKEPROG{}.  It is used
when no recovery from a particular error has been provided.

Some \PASCAL\ compilers do not implement non-local |goto| statements.
@^system dependencies@>
In such cases the code that appears at label
|end_of_MAKEPROG| should be copied into the |jump_out|
procedure, followed by a call to a system procedure that
terminates the program.

@d fatal_error(#)==begin print_nl(#); error; mark_fatal; jump_out;
  end

@<Error handling...@>=
procedure jump_out;
begin goto end_of_MAKEPROG;
end;


@                                                           % sect.   35
Sometimes the program's behavior is far different from what
it should be, and \MAKEPROG{} prints an error message that
is really for the \MAKEPROG{} maintenance person, not the
user.  In such cases the program says
|confusion('indication of where we are')|.

@d confusion(#)==fatal_error('! This can''t happen (',#,')')
@.This can't happen@>





@* The kernel.

\noindent Let us now consider the routine |get_line| that
takes care of merging |change_file| into |doc_file|.  The
|get_line| procedure also updates the line numbers for error
messages.

@<Globals...@>=
@!line:integer; {the number of the current line in the current file}
@!other_line:integer; {the number of the current line in the input file that
  is not currently being read}
@!temp_line:integer; {used when interchanging |line| with |other_line|}
@!limit:0..buf_size; {the last character position occupied in the buffer}
@!input_has_ended: boolean; {if |true|, there is no more input}
@!changing: boolean; {if |true|, the current line is from |change_file|}


@                                                           % sect.  128
As we change |changing| from |true| to |false| and back
again, we must remember to swap the values of |line| and
|other_line| so that the |err_print| routine will be sure to
report the correct line number.

@d change_changing==
         begin changing := not changing;@/
         temp_line:=other_line; other_line:=line; line:=temp_line;
         end {$|line| \BA |other_line|$}


@                                                           % sect.  129
When |changing| is |false|, the next line of |change_file|
is kept in |change_buffer[0..change_limit-1]|, for purposes
of comparison with the next line of |doc_file|.  After the
change file has been completely input, we set
|change_limit:=0|, so that no further matches will be made.

@<Globals...@>=
@!change_buffer:array[0..buf_size] of ASCII_code;
@!change_limit:0..buf_size; {the last position occupied in |change_buffer|}


@                                                           % sect.  130
Here's a simple function that checks if the two buffers are
different.

@p function lines_dont_match:boolean;
label exit;
var k:0..buf_size; {index into the buffers}
begin lines_dont_match:=true;
if change_limit<>limit then return;
if limit>0 then
  for k:=0 to limit-1 do if change_buffer[k]<>buffer[k] then return;
lines_dont_match:=false;
exit: end;


@                                                           % sect.  131
Procedure |prime_the_change_buffer| sets |change_buffer| in
preparation for the next matching operation.  Since blank
lines in the change file are not used for matching, we have
|(change_limit=0)and not changing| if and only if the change
file is exhausted.  This procedure is called only when
|changing| is true; hence error messages will be reported
correctly.

@p procedure prime_the_change_buffer;
label continue, done, exit;
var k:0..buf_size; {index into the buffers}
begin change_limit:=0; {this value will be used if the change file ends}
@<Skip over comment lines in the change file; |return| if end of file@>;
@<Skip to the next nonblank line; |return| if end of file@>;
@<Move |buffer| and |limit| to |change_buffer| and |change_limit|@>;
exit: end;


@                                                           % sect.  132
While looking for a line that begins with \.{@@x} in the
change file, we allow lines that begin with \.{@@}, as long
as they don't begin with \.{@@y} or \.{@@z} (which would
probably indicate that the change file is fouled up).

@<Skip over comment lines in the change file...@>=
loop@+  begin incr(line);
  if not input_ln(change_file) then return;
  if limit<2 then goto continue;
  if buffer[0]<>"@@" then goto continue;
  if (buffer[1]>="X")and(buffer[1]<="Z") then
    buffer[1]:=buffer[1]+"z"-"Z"; {lowercasify}
  if buffer[1]="x" then goto done;
  if (buffer[1]="y")or(buffer[1]="z") then
    err_print('! Where is the matching @@x?');
@.Where is the match...@>
continue: end;
done:


@                                                           % sect.  133
Here we are looking at lines following the \.{@@x}.

@<Skip to the next nonblank line...@>=
repeat incr(line);
  if not input_ln(change_file) then
    begin err_print('! Change file ended after @@x');
@.Change file ended...@>
    return;
    end;
until limit>0;


@                                                           % sect.  134
@<Move |buffer| and |limit| to |change_buffer| and |change_limit|@>=
begin change_limit:=limit;
for k:=0 to limit-1 do change_buffer[k]:=buffer[k];
end


@                                                           % sect.  135
The following procedure is used to see if the next change
entry should go into effect; it is called only when
|changing| is false.  The idea is to test whether or not the
current contents of |buffer| matches the current contents of
|change_buffer|.  If not, there's nothing more to do; but if
so, a change is called for:  All of the text down to the
\.{@@y} is supposed to match.  An error message is issued if
any discrepancy is found.  Then the procedure prepares to
read the next line from |change_file|.

@p
procedure check_change; {switches to |change_file| if the buffers match}
label exit;
var n:integer; {the number of discrepancies found}
@!k:0..buf_size; {index into the buffers}
begin if lines_dont_match then return;
n:=0;
loop@+  begin change_changing; {now it's |true|}
  incr(line);
  if not input_ln(change_file) then
    begin err_print('! Change file ended before @@y');@/
@.Change file ended...@>
    change_limit:=0;  change_changing; {|false| again}
    return;
    end;
  @<If the current line starts with \.{@@y},
    report any discrepancies and |return|@>;
  @<Move |buffer| and |limit|...@>;
  change_changing; {now it's |false|}
  incr(line);
  if not input_ln(doc_file) then
    begin err_print('! CWEB file ended during a change');
@.CWEB file ended...@>
    input_has_ended:=true; return;
    end;
  if lines_dont_match then incr(n);
  end;
exit: end;


@                                                           % sect.  136
@<If the current line starts with \.{@@y}...@>=
if limit>1 then if buffer[0]="@@" then
  begin if (buffer[1]>="X")and(buffer[1]<="Z") then
    buffer[1]:=buffer[1]+"z"-"Z"; {lowercasify}
  if (buffer[1]="x")or(buffer[1]="z") then
    err_print('! Where is the matching @@y?')
@.Where is the match...@>
  else if buffer[1]="y" then
    begin if n>0 then
      err_print('! Hmm... ',n:1,' of the preceding lines failed to match');
@.Hmm... n of the preceding...@>
    return;
    end;
  end


@                                                           % sect.  137
@< Initialize the input system @>=
begin line:=0; other_line:=0;@/
changing:=true; prime_the_change_buffer; change_changing;@/
limit:=0; buffer[0]:=" "; input_has_ended:=false;
end


@                                                           % sect.  138
The |get_line| procedure puts the next line of merged input
into the buffer and updates the other variables
appropriately.  A space is placed at the right end of the
line.  We output points to show the user the progress in
reading.

@p
procedure get_line; {inputs the next line}
   label restart;
   begin
restart: if changing then
      @<Read from |change_file| and maybe turn off |changing|@>;
   if not changing then
      begin @<Read from |doc_file| and maybe turn on |changing|@>;
      if changing then  goto restart;
      end;
   buffer[limit]:=" ";
   if (line mod 500) = 0 then
      begin print(line:1);  update_terminal;
      end
   else if (line mod 100) = 0 then
         begin print('.');  update_terminal;
         end
      @!debug else begin print('.');  update_terminal; @+ end @+ gubed @;
      ;@/
   end;


@                                                           % sect.  139
@<Read from |doc_file|...@>=
begin incr(line);
if not input_ln(doc_file) then input_has_ended:=true
else if change_limit>0 then check_change;
end


@                                                           % sect.  140
@<Read from |change_file|...@>=
begin incr(line);
if not input_ln(change_file) then
  begin err_print('! Change file ended without @@z');
@.Change file ended...@>
  buffer[0]:="@@"; buffer[1]:="z"; limit:=2;
  end;
if limit>1 then {check if the change has ended}
  if buffer[0]="@@" then
    begin if (buffer[1]>="X")and(buffer[1]<="Z") then
      buffer[1]:=buffer[1]+"z"-"Z"; {lowercasify}
    if (buffer[1]="x")or(buffer[1]="y") then
      err_print('! Where is the matching @@z?')
@.Where is the match...@>
    else if buffer[1]="z" then
      begin prime_the_change_buffer; change_changing;
      end;
    end;
end


@                                                           % sect.  141
At the end of the program, we will tell the user if the
change file had a line that didn't match any relevant line
in |doc_file|.

@<Check that all changes have been read@>=
begin
if change_limit<>0 then {|changing| is false}
   begin
   for limit:=0 to change_limit do  buffer[limit] := change_buffer[limit];
   limit := change_limit;  changing := true;  line := other_line;
   err_print('! Change file entry did not match');
@.Change file entry did not match@>
   end;
end


@
The |put_line| procedure outputs the next line from
|buffer| to |prog_file|. Perhaps we should give here a
progress report, too (with asterisks?)

@p
procedure put_line;
   var i: 0..buf_size;
   begin
   for i:=0 to limit-1 do  write(prog_file, xchr[buffer[i]]);
   write_ln(prog_file);
   end;





@* The main program.                                        % sect.  190

\noindent We have defined some procedures, and it is time to
use them---here is where \MAKEPROG{} starts, and where it
ends.
@^system dependencies@>

@p
   begin initialize;
   print_ln(banner); {print a ``banner line''}
   print_ln(copy_right); print_ln(rights_res); {print a copyright notice}
   @< Initialize the input system @>;
   debug  print_ln('begin copy');
   gubed @;
   @< Copy all program parts to the output @>;
   debug  print_ln('end copy');
   gubed @;
   @< Check that all changes... @>;
end_of_MAKEPROG:
   @#
   {here files should be closed if the operating system requires it}
   @;@#
   @<Print the job |history|@>;
   end.


@
A program part begins after a line that begins with
\.{\\beginprog} and ends before the next line with
\.{\\endprog} starting it. If we find the starting line we
set |state| to |begin_prog|, between to lines |state| has
the value |inner_prog| and with the ending line |state| is
set to |out_of_prog|.

@d begin_prog = 0
@d inner_prog = 1
@d out_of_prog = 2

@< Glob... @>=
@!state: begin_prog..out_of_prog;

@
@< Set init... @>=
state := out_of_prog;


@
After we have read the introducing line for a program part
which is signaled with |state=begin_prog| we change the
state to |inner_prog| to start copy the next line;

@< Copy all program... @>=
begin get_line;
while not input_has_ended do
   begin @< Look at the input line and store in |state| the result @>;
   if state = inner_prog then  put_line
   else if state = begin_prog then  state := inner_prog;
   get_line;
   end;
if state = inner_prog then  err_print('! Input has ended prematurely');
@.Input has ended...@>
end


@
We first define a few macros to improve the readability of
the program part behind. After \.{\\beginprog} no letters
may appear and after \.{\\endprog} either the line is ended
or white space is to be there. The comparison is facilitated
by the fact that |buffer[limit]=" "|, i.e.\ the last
character of a line is always a space.

@d cmp_prog(#) == (buffer[#]="p") and (buffer[#+1]="r") and
                  (buffer[#+2]="o") and (buffer[#+3]="g")
@d cmp_begin == (buffer[1]="b") and (buffer[2]="e") and (buffer[3]="g") and@|
                (buffer[4]="i") and (buffer[5]="n") and cmp_prog(6) and@|
                ((buffer[10]<"A") or (buffer[10]>"Z")) and@|
                ((buffer[10]<"a") or (buffer[10]>"z"))
@d cmp_end == (buffer[1]="e") and (buffer[2]="n") and (buffer[3]="d") and
              cmp_prog(4) and @|
              ((buffer[8]=" ") or (buffer[8]=tab_mark))

@< Look at the input... @>=
begin
if buffer[0] = "\" then
   if limit >= 10 then
      begin @+ if cmp_begin then  state := begin_prog;  @+ end
   else if limit >= 8 then
      if cmp_end then  state := out_of_prog;
end


@                                                           % sect.  195
Some implementations may wish to pass the |history| value to the
operating system so that it can be used to govern whether or not other
programs are started. Here we simply report the history to the user.
@^system dependencies@>

@<Print the job |history|@>=
case history of
spotless: print_nl('(No errors were found.)');
harmless_message: print_nl('(Did you see the warning message above?)');
error_message: print_nl('(Pardon me, but I think I spotted something wrong.)');
fatal_message: print_nl('(That was a fatal error, my friend.)');
end {there are no other cases}





@* System-dependent changes.                                % sect.  196

\noindent This module should be replaced, if necessary, by
changes to the program that are necessary to make
\MAKEPROG{} work at a particular installation.  It is
usually best to design your change file so that all changes
to previous modules preserve the module numbering; then
everybody's version will be consistent with the printed
program.  More extensive changes, which introduce new
modules, can be inserted here; then only the index itself
will get a new module number.
@^system dependencies@>





@* Index.                                                   % sect.  197

\noindent Here is a cross-reference table for the
\MAKEPROG{} processor.  All modules in which an identifier
is used are listed with that identifier, except that
reserved words are indexed only when they appear in format
definitions, and the appearances of identifiers in module
names are not indexed.  Underlined entries correspond to
where the identifier was declared.  Error messages and a few
other things like ``system dependencies'' are indexed here
too.