%   Change file for the TANGLE processor, for use with GNU Pascal.
%   This file was created by Don Knuth, based on the original
%   UNIX port by Howard Trickey, Pavel Curtis, et al.
%   (See ../web-sparc for details of that work.)

% History:
%  2000.04.29   Original version

% NOTE: The module numbers refer to the standard WEB manual (CS 980).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [0] WEAVE: print changes only
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
\pageno=\contentspagenumber \advance\pageno by 1
@y
\pageno=\contentspagenumber \advance\pageno by 1
\let\maybe=\iffalse
\def\title{TANGLE changes for {\mc GNU} Pascal}
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [1] Change banner message
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
@d banner=='This is TANGLE, Version 4.5'
@y
@d banner=='This is TANGLE, Version 4.5 for Linux'
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [2] add input and output, remove other files, add ref to scan_args,
% [2]       and #include external definition for exit(), etc.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
program TANGLE(@!web_file,@!change_file,@!Pascal_file,@!pool);
label end_of_TANGLE; {go here to finish}
const @<Constants in the outer block@>@/
type @<Types in the outer block@>@/
var @<Globals in the outer block@>@/
@<Error handling procedures@>@/
@y
program TANGLE(@!input,@!output);
label end_of_TANGLE; {go here to finish}
const @<Constants in the outer block@>@/
type @<Types in the outer block@>@/
var @<Globals in the outer block@>@/
@\
@=#include "tangext.h"@>
@\@/
@<Error handling procedures@>@/
@<Declaration of |scan_args|@>@/
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [4] compiler options
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
@{@&$C-,A+,D-@} {no range check, catch arithmetic overflow, no debug overhead}
@!debug @{@&$C+,D+@}@+ gubed {but turn everything on when debugging}
@y
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [7] Fix others:
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
@d othercases == others: {default for cases not listed explicitly}
@y
@d othercases == otherwise {ISO extended Pascal default cases}
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [8] keep long identifier names
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
@!max_id_length=12; {long identifiers are chopped to this length, which must
  not exceed |line_length|}
@y
@!max_id_length=50; {long identifiers are chopped to this length, which must
  not exceed |line_length|}
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [11] make ASCII codes take 1 byte (not 4 or more!)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
@!ASCII_code=0..255; {eight-bit numbers, a subrange of the integers}
@y
@!ASCII_code=ByteCard; {eight-bit numbers, a subrange of the integers}
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [12] make the compiler recognize a text file as text
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
@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=255 {ordinal number of the largest element of |text_char|}

@<Types...@>=
@!text_file=packed file of text_char;
@y
@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=255 {ordinal number of the largest element of |text_char|}
@d text_file==text
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [13] xchr and xord now external
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
@!xord: array [text_char] of ASCII_code;
  {specifies conversion of input characters}
@!xchr: array [ASCII_code] of text_char;
  {specifies conversion of output characters}
@y
@!xord: external array [text_char] of ASCII_code;
  {specifies conversion of input characters}
@!xchr: external array [ASCII_code] of text_char;
  {specifies conversion of output characters}
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [17] enable maximum character set
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
for i:=1 to @'37 do xchr[i]:=' ';
for i:=@'200 to @'377 do xchr[i]:=' ';
@y
for i:=1 to @'37 do xchr[i]:=chr(i);
for i:=@'200 to @'377 do xchr[i]:=chr(i);
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [20] terminal output: use standard i/o
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
@d print(#)==write(term_out,#) {`|print|' means write on the terminal}
@y
@d term_out==output
@d print(#)==write(term_out,#) {`|print|' means write on the terminal}
@z

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

@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [21] init terminal
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
@ 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}
@y
@ Different systems have different ways of specifying that the output on a
certain file will appear on the user's terminal.
@^system dependencies@>

@<Set init...@>=
 {Nothing need be done on Linux}
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [22] flush terminal buffer
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
@d update_terminal == break(term_out) {empty the terminal output buffer}
@y
@d update_terminal == flush_stdout {empty the terminal output buffer}
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [24] open input files
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
@ 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@>

@p procedure open_input; {prepare to read |web_file| and |change_file|}
begin reset(web_file); reset(change_file);
end;
@y
@ The following code opens the input files.
This happens after the initialize procedure has executed.
That will have called the |scan_args| procedure to set up the global
variables |web_name| and |change_name| to the appropriate file
names.
These globals, and the |scan_args| procedure will be defined at the end
where they won't disturb the module numbering.
@^system dependencies@>

@p procedure open_input; {prepare to read |web_file| and |change_file|}
begin
reset(web_file,web_name); reset(change_file,change_name);
end;
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [26] open output files
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
@ The following code opens |Pascal_file| and |pool|.
Since these files were listed in the program header, we assume that the
\PASCAL\ runtime system has checked that suitable external file names have
been given.
@^system dependencies@>

@<Set init...@>=
rewrite(Pascal_file); rewrite(pool);
@y
@ The following code opens |Pascal_file| and |pool|.
Use the |scan_args| procedure to fill the global file names,
according to the names given on the command line.
@^system dependencies@>

@<Set init...@>=
scan_args;
rewrite(Pascal_file,Pascal_name); rewrite(pool,pool_name);
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [27] buffer now external
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
@<Globals...@>=@!buffer: array[0..buf_size] of ASCII_code;
@y
@<Globals...@>=@!buffer: external array[0..buf_size] of ASCII_code;
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [28] faster input_ln
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
@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]<>" " then final_limit:=limit;
    if limit=buf_size then
      begin while not eoln(f) do get(f);
      decr(limit); {keep |buffer[buf_size]| empty}
      if final_limit>limit then final_limit:=limit;
      print_nl('! Input line too long'); loc:=0; error;
@.Input line too long@>
      end;
    end;
  read_ln(f); limit:=final_limit; input_ln:=true;
  end;
end;
@y
With Linux we call an external C procedure, |line_read|.
That routine fills |buffer| from 0 onwards with the |xord|'ed values
of the next line, setting |limit| appropriately (ignoring trailing
blanks).
It will stop if |limit=buf_size|, and the following will cause an error
message.

@p function input_ln(var f:text_file):boolean;
  {inputs a line or returns |false|}
begin limit:=0;
if test_eof(f) then input_ln:=false
else  begin line_read(f);
    if limit=buf_size then
      begin
      decr(limit); {keep |buffer[buf_size]| empty}
      print_nl('! Input line too long'); loc:=0; error;
@.Input line too long@>
      end;
   input_ln:=true;
  end;
end;
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [38] Data Structures: provide for larger |byte_mem| and |tok_mem|
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x Extra capacity:
@d ww=2 {we multiply the byte capacity by approximately this amount}
@d zz=3 {we multiply the token capacity by approximately this amount}
@y
@d ww=3 {we multiply the byte capacity by approximately this amount}
@d zz=4 {we multiply the token capacity by approximately this amount}
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [89] Work around a bug in GPC version 2.8.1
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
othercases confusion('output')
@y ('otherwise' syntax not recognized when there's a case inside a case!)
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [105] Accept DIV, div, MOD, and mod
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
 (((out_contrib[1]="D")and(out_contrib[2]="I")and(out_contrib[3]="V")) or@|
 ((out_contrib[1]="M")and(out_contrib[2]="O")and(out_contrib[3]="D")) ))or@|
@^uppercase@>
@y
  (((out_contrib[1]="D")and(out_contrib[2]="I")and(out_contrib[3]="V")) or@|
  ((out_contrib[1]="d")and(out_contrib[2]="i")and(out_contrib[3]="v")) or@|
  ((out_contrib[1]="M")and(out_contrib[2]="O")and(out_contrib[3]="D")) or@|
  ((out_contrib[1]="m")and(out_contrib[2]="o")and(out_contrib[3]="d")) ))or@|
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [110] lowercase ids
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
@^uppercase@>
  if ((out_buf[out_ptr-3]="D")and(out_buf[out_ptr-2]="I")and
    (out_buf[out_ptr-1]="V"))or @/
     ((out_buf[out_ptr-3]="M")and(out_buf[out_ptr-2]="O")and
    (out_buf[out_ptr-1]="D")) then@/ goto bad_case
@y
  if ((out_buf[out_ptr-3]="D")and(out_buf[out_ptr-2]="I")and
    (out_buf[out_ptr-1]="V"))or @/
     ((out_buf[out_ptr-3]="d")and(out_buf[out_ptr-2]="i")and
    (out_buf[out_ptr-1]="v"))or @/
     ((out_buf[out_ptr-3]="M")and(out_buf[out_ptr-2]="O")and
    (out_buf[out_ptr-1]="D"))or @/
     ((out_buf[out_ptr-3]="m")and(out_buf[out_ptr-2]="o")and
    (out_buf[out_ptr-1]="d")) then@/ goto bad_case
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [114] lowercase operators (`and', `or', etc.)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
and_sign: begin out_contrib[1]:="A"; out_contrib[2]:="N"; out_contrib[3]:="D";
@^uppercase@>
  send_out(ident,3);
  end;
not_sign: begin out_contrib[1]:="N"; out_contrib[2]:="O"; out_contrib[3]:="T";
  send_out(ident,3);
  end;
set_element_sign: begin out_contrib[1]:="I"; out_contrib[2]:="N";
  send_out(ident,2);
  end;
or_sign: begin out_contrib[1]:="O"; out_contrib[2]:="R"; send_out(ident,2);
@y
and_sign: begin out_contrib[1]:="a"; out_contrib[2]:="n"; out_contrib[3]:="d";
  send_out(ident,3);
  end;
not_sign: begin out_contrib[1]:="n"; out_contrib[2]:="o"; out_contrib[3]:="t";
  send_out(ident,3);
  end;
set_element_sign: begin out_contrib[1]:="i"; out_contrib[2]:="n";
  send_out(ident,2);
  end;
or_sign: begin out_contrib[1]:="o"; out_contrib[2]:="r"; send_out(ident,2);
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [116] Remove conversion to uppercase
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
@ Single-character identifiers represent themselves, while longer ones
appear in |byte_mem|. All must be converted to uppercase,
with underlines removed. Extremely long identifiers must be chopped.

(Some \PASCAL\ compilers work with lowercase letters instead of
uppercase. If this module of \.{TANGLE} is changed, it's also necessary
to change from uppercase to lowercase in the modules that are
listed in the index under ``uppercase''.)
@^system dependencies@>
@^uppercase@>

@d up_to(#)==#-24,#-23,#-22,#-21,#-20,#-19,#-18,#-17,#-16,#-15,#-14,
  #-13,#-12,#-11,#-10,#-9,#-8,#-7,#-6,#-5,#-4,#-3,#-2,#-1,#

@<Cases related to identifiers@>=
"A",up_to("Z"): begin out_contrib[1]:=cur_char; send_out(ident,1);
  end;
"a",up_to("z"): begin out_contrib[1]:=cur_char-@'40; send_out(ident,1);
  end;
identifier: begin k:=0; j:=byte_start[cur_val]; w:=cur_val mod ww;
  while (k<max_id_length)and(j<byte_start[cur_val+ww]) do
    begin incr(k); out_contrib[k]:=byte_mem[w,j]; incr(j);
    if out_contrib[k]>="a" then out_contrib[k]:=out_contrib[k]-@'40
    else if out_contrib[k]="_" then decr(k);
    end;
  send_out(ident,k);
  end;
@y
@ Single-character identifiers represent themselves, while longer ones
appear in |byte_mem|. All must be converted to lowercase,
with underlines removed. Extremely long identifiers must be chopped.
@^system dependencies@>

@d up_to(#)==#-24,#-23,#-22,#-21,#-20,#-19,#-18,#-17,#-16,#-15,#-14,
  #-13,#-12,#-11,#-10,#-9,#-8,#-7,#-6,#-5,#-4,#-3,#-2,#-1,#

@<Cases related to identifiers@>=
"A",up_to("Z"),
"a",up_to("z"): begin out_contrib[1]:=cur_char; send_out(ident,1);
  end;
identifier: begin k:=0; j:=byte_start[cur_val]; w:=cur_val mod ww;
  while (k<max_id_length)and(j<byte_start[cur_val+ww]) do
    begin incr(k); out_contrib[k]:=byte_mem[w,j]; incr(j);
    if out_contrib[k]="_" then decr(k);
    end;
  send_out(ident,k);
  end;
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [124] limit is now set by lineread procedure
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
@!limit:0..buf_size; {the last character position occupied in the buffer}
@y
@!limit:external integer; {the last character position occupied in the buffer}
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [179] make term_in = input
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
any error stop will set |debug_cycle| to zero.
@y
any error stop will set |debug_cycle| to zero.

@d term_in==input
@z

@x
@!term_in:text_file; {the user's terminal as an input file}
@y

@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [180] remove term_in reset
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
reset(term_in,'TTY:','/I'); {open |term_in| as the terminal, don't do a |get|}
@y

@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [182] write newline just before exit; use value of |history|
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
We have defined plenty of procedures, and it is time to put the last
pieces of the puzzle in place. Here is where \.{TANGLE} starts, and where
it ends.
@^system dependencies@>
@y
We have defined plenty of procedures, and it is time to put the last
pieces of the puzzle in place. Here is where \.{TANGLE} starts, and where
it ends.
@^system dependencies@>

@d UNIXexit==e@&x@&i@&t
@z

@x
@<Print the job |history|@>;
@y
@<Print the job |history|@>;
new_line;
if (history <> spotless) and (history <> harmless_message) then
    UNIXexit(1)
else
    UNIXexit(0);
@z

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [188] system dependent changes--the |scan_args| procedure.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@x
@* System-dependent changes.
This module should be replaced, if necessary, by changes to the program
that are necessary to make \.{TANGLE} 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@>
@y
@* System-dependent changes.
@^system dependencies@>

@ The user calls \.{TANGLE} with arguments on the command line.
These are either file names or flags (beginning with '-').
The following globals are for communicating the user's desires to the rest
of the program. The various |file_name| variables contain strings with
the full names of those files, as UNIX knows them.

There are no flags that affect \.{TANGLE} at the moment.

@d max_file_name_length==60

@<Globals...@>=
@!web_name,@!change_name,@!Pascal_name,@!pool_name:
        UNIX_filename;

@ @<Types...@>=
UNIX_filename=packed array[1..max_file_name_length] of char;

@ The |scan_args| procedure looks at the command line arguments and sets
the |file_name| variables accordingly.
At least one file name must be present: the \.{WEB} file.  It may have
an extension, or it may omit it to get |'.web'| added.
The \PASCAL\ output file name is formed by replacing the \.{WEB} file
name extension by |'.p'|.
Similarly, the pool file name is formed using a |'.pool'| extension.

If there is another file name present among the arguments, it is the
change file, again either with an extension or without one to get |'.ch'|
An omitted change file argument means that |'/dev/null'| should be used,
when no changes are desired.

@<Declaration of |scan_args|@>=
procedure scan_args;
var dot_pos,i,a: integer; {indices}
c: char;
@!fname: UNIX_filename; {temporary argument holder}
@!found_web,@!found_change: boolean; {|true| when those file names have
                                        been seen}
begin
found_web:=false;
found_change:=false;
for a:=1 to argc-1 do begin
        argv(a,fname); {put argument number |a| into |fname|}
        if fname[1]<>'-' then begin
                if not found_web then
                        @<Get |web_name|, |Pascal_name|, and
                                | pool_name| variables from |fname|@>
                else if not found_change then
                        @<Get |change_name| from |fname|@>
                else  @<Print usage error message and quit@>;
                end
        else @<Handle flag argument in |fname|@>;
        end;
if not found_web then @<Print usage error message and quit@>;
if not found_change then @<Set up null change file@>;
end;

@ Use all of |fname| for the |web_name| if there is a |'.'| in it,
otherwise add |'.web'|.
The other file names come from adding things after the dot.
The |argv| procedure will not put more than |max_file_name_length-5|
characters into |fname|, and this leaves enough room in the |file_name|
variables to add the extensions.

The end of a file name is marked with a |chr(0)|, the convention assumed by 
the |argv| and |reset| and |rewrite| procedures.

@<Get |web_name|...@>=
begin
dot_pos:=-1;
i:=1;
while (fname[i]<>chr(0)) and (i<=max_file_name_length-5) do begin
        web_name[i]:=fname[i];
        if fname[i]='.' then dot_pos:=i;
        incr(i);
        end;
if dot_pos=-1 then begin
        dot_pos:=i;
        web_name[dot_pos]:='.';
        web_name[dot_pos+1]:='w';
        web_name[dot_pos+2]:='e';
        web_name[dot_pos+3]:='b';
        web_name[dot_pos+4]:=chr(0);
        end
else web_name[i]:=chr(0);
for i:=1 to dot_pos do begin
        c:=web_name[i];
        Pascal_name[i]:=c;
        pool_name[i]:=c;
        end;
Pascal_name[dot_pos+1]:='p';
Pascal_name[dot_pos+2]:=chr(0);
pool_name[dot_pos+1]:='p';
pool_name[dot_pos+2]:='o';
pool_name[dot_pos+3]:='o';
pool_name[dot_pos+4]:='l';
pool_name[dot_pos+5]:=chr(0);
found_web:=true;
end

@ @<Get |change_name|...@>=
begin
dot_pos:=-1;
i:=1;
while (fname[i]<>chr(0)) and (i<=max_file_name_length-5)
do begin
        change_name[i]:=fname[i];
        if fname[i]='.' then dot_pos:=i;
        incr(i);
        end;
if dot_pos=-1 then begin
        dot_pos:=i;
        change_name[dot_pos]:='.';
        change_name[dot_pos+1]:='c';
        change_name[dot_pos+2]:='h';
        change_name[dot_pos+3]:=chr(0);
        end
else change_name[i]:=chr(0);
found_change:=true;
end

@ @<Set up null...@>=
begin
        change_name[1]:='/';
        change_name[2]:='d';
        change_name[3]:='e';
        change_name[4]:='v';
        change_name[5]:='/';
        change_name[6]:='n';
        change_name[7]:='u';
        change_name[8]:='l';
        change_name[9]:='l';
        change_name[10]:=chr(0);
end

@ There are no flags currently used by \.{TANGLE}, but this module can be
used as a hook to introduce flags.

@<Handle flag...@>=
begin
	@<Print usage error message and quit@>;
end

@ @<Print usage error message and quit@>=
begin
print_nl('! Usage: tangle webfile[.web] [changefile[.ch]]');
error;
jump_out;
end

@z