path: root/language/xettex/waits-xe.ch

@x Tell WEAVE to print only the changes:
  \def\?##1]{\hbox to 1in{\hfil##1.\ }}
  }
@y
  \def\?##1]{\hbox{Changes to \hbox to 1em{\hfil##1}.\ }}
  }
\let\maybe=\iffalse
@z

@x WAITS's banner: [2]
@d banner=='This is TeX, Version 2.0' {printed when \TeX\ starts}
@y
@d banner=='This is TeX-XeT, WAITS Version 2.0' {printed when \TeX\ starts}
@z

@x Switches for debugging and statistics: (7)
@d debug==@{ {change this to `$\\{debug}\equiv\null$' when debugging}
@d gubed==@t@>@} {change this to `$\\{gubed}\equiv\null$' when debugging}
@f debug==begin
@f gubed==end
@#
@d stat==@{ {change this to `$\\{stat}\equiv\null$' when gathering
  usage statistics}
@d tats==@t@>@} {change this to `$\\{tats}\equiv\null$' when gathering
  usage statistics}
@f stat==begin
@f tats==end
@y
@d debug== {change this to `$\\{debug}\equiv\null$' when debugging}
@d gubed== {change this to `$\\{gubed}\equiv\null$' when debugging}
@f debug==begin
@f gubed==end
@#
@d stat== {change this to `$\\{stat}\equiv\.{@@\{}$' when not
  gathering usage statistics}
@d tats== {change this to `$\\{tats}\equiv\.{@@\}}$' when not
  gathering usage statistics}
@f stat==begin
@f tats==end
@z

@x The INITEX switch: (8)
@d init== {change this to `$\\{init}\equiv\.{@@\{}$' in the production version}
@d tini== {change this to `$\\{tini}\equiv\.{@@\}}$' in the production version}
@y [In this case, no change is made]
@d init== {change this to `$\\{init}\equiv\.{@@\{}$' in the production version}
@d tini== {change this to `$\\{tini}\equiv\.{@@\}}$' in the production version}
@z

@x Compiler directives: (9)
@{@&$C-,A+,D-@} {no range check, catch arithmetic overflow, no debug overhead}
@!debug @{@&$C+,D+@}@+ gubed {but turn everything on when debugging}
@y
@{@&$C-,A+,D-,W+,H:0@}
  {no range check, catch arithmetic overflow, no debug overhead, no heap}
@!debug @{@&$C+,D:5,W+@}@+ gubed {but turn everything on when debugging}
{the `|W+|' switch catches more syntax errors}
{the `\ignorespaces|D:5|' avoids initial stop for the debugger}
@z

@x Compile-time constants: [11]
@!mem_max=30000; {greatest index in \TeX's internal |mem| array;
  must be strictly less than |max_halfword|;
  must be equal to |mem_top| in \.{INITEX}, otherwise |>=mem_top|}
@!mem_min=0; {smallest index in \TeX's internal |mem| array;
  must be |min_halfword| or more;
  must be equal to |mem_bot| in \.{INITEX}, otherwise |<=mem_bot|}
@!buf_size=500; {maximum number of characters simultaneously present in
  current lines of open files and in control sequences between
  \.{\\csname} and \.{\\endcsname}; must not exceed |max_halfword|}
@!error_line=72; {width of context lines on terminal error messages}
@!half_error_line=42; {width of first lines of contexts in terminal
  error messages; should be between 30 and |error_line-15|}
@!max_print_line=79; {width of longest text lines output; should be at least 60}
@!stack_size=200; {maximum number of simultaneous input sources}
@!max_in_open=6; {maximum number of input files and error insertions that
  can be going on simultaneously}
@!font_max=75; {maximum internal font number; must not exceed |max_quarterword|
  and must be at most |font_base+256|}
@!font_mem_size=20000; {number of words of |font_info| for all fonts}
@!param_size=60; {maximum number of simultaneous macro parameters}
@!nest_size=40; {maximum number of semantic levels simultaneously active}
@!max_strings=3000; {maximum number of strings; must not exceed |max_halfword|}
@!string_vacancies=8000; {the minimum number of characters that should be
  available for the user's control sequences and font names,
  after \TeX's own error messages are stored}
@!pool_size=32000; {maximum number of characters in strings, including all
  error messages and help texts, and the names of all fonts and
  control sequences; must exceed |string_vacancies| by the total
  length of \TeX's own strings, which is currently about 23000}
@!save_size=600; {space for saving values outside of current group; must be
  at most |max_halfword|}
@!trie_size=8000; {space for hyphenation patterns; should be larger for
  \.{INITEX} than it is in production versions of \TeX}
@!dvi_buf_size=800; {size of the output buffer; must be a multiple of 8}
@!file_name_size=40; {file names shouldn't be longer than this}
@!pool_name='TeXformats:TEX.POOL                     ';
  {string of length |file_name_size|; tells where the string pool appears}
@.TeXformats@>
@y
@!mem_max=32000; {greatest index in \TeX's internal |mem| array;
  must be strictly less than |max_halfword|;
  must be equal to |mem_top| in \.{INITEX}, otherwise |>=mem_top|}
@!mem_min=16000; {smallest index in \TeX's internal |mem| array;
  must be |min_halfword| or more;
  must be equal to |mem_bot| in \.{INITEX}, otherwise |<=mem_bot|}
@!buf_size=500; {maximum number of characters simultaneously present in
  current lines of open files and in control sequences between
  \.{\\csname} and \.{\\endcsname}; must not exceed |max_halfword|}
@!error_line=80; {width of context lines on terminal error messages}
@!half_error_line=50; {width of first lines of contexts in terminal
  error messages; should be between 30 and |error_line-15|}
@!max_print_line=80; {width of longest text lines output; should be at least 60}
@!stack_size=200; {maximum number of simultaneous input sources}
@!max_in_open=6; {maximum number of input files and error insertions that
  can be going on simultaneously}
@!font_max=100;
  {maximum internal font number; must not exceed |max_quarterword|}
@!font_mem_size=23000; {number of words of |font_info| for all fonts}
@!param_size=60; {maximum number of simultaneous macro parameters}
@!nest_size=40; {maximum number of semantic levels simultaneously active}
@!max_strings=3500; {maximum number of strings}
@!string_vacancies=8000; {the minimum number of characters that should be
  available for the user's control sequences and font names,
  after \TeX's own error messages are stored}
@!pool_size=40000; {maximum number of characters in strings, including all
  error messages and help texts, and the names of all fonts and
  control sequences; must exceed |string_vacancies| by the total
  length of \TeX's own strings, which is currently about 22500}
@!save_size=300; {space for saving values outside of current group; must be
  at most |max_halfword|}
@!trie_size=8000; {space for hyphenation patterns; should be larger for
  \.{INITEX} than it is in production versions of \TeX}
@!dvi_buf_size=800; {size of the output buffer; must be a multiple of 8}
@!file_name_size=23; {file names shouldn't be longer than this}
@!pool_name='XET.POOL[XET,DEK]      ';
  {string of length |file_name_size|; tells where the string pool appears}
@z

@x TANGLE-time constants: (12)
@d mem_bot=0 {smallest index in the |mem| array dumped by \.{INITEX};
  must not be less than |mem_min|}
@d mem_top==30000 {largest index in the |mem| array dumped by \.{INITEX};
  must be substantially larger than |mem_bot|
  and not greater than |mem_max|}
@d font_base=0 {smallest internal font number; must not be less
  than |min_quarterword|}
@d hash_size=2100 {maximum number of control sequences; it should be at most
  about |(mem_max-mem_min)/10|, but 2100 is already quite generous}
@d hash_prime=1777 {a prime number equal to about 85\% of |hash_size|}
@d hyph_size=307 {another prime; the number of \.{\\hyphenation} exceptions}
@y
@d mem_bot=16000 {smallest index in the |mem| array dumped by \.{INITEX};
  must not be less than |mem_min|}
@d mem_top==32000 {largest index in the |mem| array dumped by \.{INITEX};
  must be substantially larger than |mem_bot|
  and not greater than |mem_max|}
@d font_base=0 {smallest internal font number; must not be less
  than |min_quarterword|}
@d hash_size=2500 {maximum number of control sequences; it should be at most
  about |(mem_max-mem_min)/10|, but 2100 is already quite generous}
@d hash_prime=2113 {a prime number equal to about 85\% of |hash_size|}
@d hyph_size=307 {another prime; the number of \.{\\hyphenation} exceptions}
@z

@x System-dependent character set changes: (23)
@^character set dependencies@>
@^system dependencies@>

@<Set init...@>=
for i:=1 to @'37 do xchr[i]:=' ';
@y
@^character set dependencies@>
@^system dependencies@>

The code shown here is intended to be used on the Stanford {\sc SAIL} system,
and at other installations like CMU and ISI where essentially the same
extended character set is used. The fact that {\mc SAIL} has |'}'| in the
wrong place turns out to cause no difficulty in this case.

@<Set initial values...@>=
for i:=1 to @'37 do xchr[i]:=chr(i);
xchr[@'30]:=chr(@'137);
xchr[@'32]:=chr(@'33); {|not_equal| sign}
xchr[@'33]:=chr(@'176);
@z

@x Opening files: (27)
@d reset_OK(#)==erstat(#)=0
@d rewrite_OK(#)==erstat(#)=0

@p function a_open_in(var f:alpha_file):boolean;
  {open a text file for input}
begin reset(f,name_of_file,'/O'); a_open_in:=reset_OK(f);
end;
@#
function a_open_out(var f:alpha_file):boolean;
  {open a text file for output}
begin rewrite(f,name_of_file,'/O'); a_open_out:=rewrite_OK(f);
end;
@#
function b_open_in(var f:byte_file):boolean;
  {open a binary file for input}
begin reset(f,name_of_file,'/O'); b_open_in:=reset_OK(f);
end;
@#
function b_open_out(var f:byte_file):boolean;
  {open a binary file for output}
begin rewrite(f,name_of_file,'/O'); b_open_out:=rewrite_OK(f);
end;
@#
function w_open_in(var f:word_file):boolean;
  {open a word file for input}
begin reset(f,name_of_file,'/O'); w_open_in:=reset_OK(f);
end;
@#
function w_open_out(var f:word_file):boolean;
  {open a word file for output}
begin rewrite(f,name_of_file,'/O'); w_open_out:=rewrite_OK(f);
end;
@y
@d reset_OK(#)==erstat(#) mod @'20000 = 0
@d rewrite_OK(#)==erstat(#) mod @'20000 = 0

@p function erstat(var f:file):integer; extern;@t/2@>
@#
function a_open_in(var f:alpha_file):boolean;
  {open a text file for input}
begin reset(f,name_of_file,'/E/O/N:9');
  {the \.{/E} switch distinguishes |form_feed| from |carriage_return|;
  the \.{/O} switch gives error control to us;
  and the \.{/N:9} switch specifies 9 buffers, which
  seems to work satisfactorily at {\mc SAIL}}
a_open_in:=reset_OK(f);
end;
@#
function a_open_out(var f:alpha_file):boolean;
  {open a text file for output}
begin rewrite(f,name_of_file,'/O/N:2'); a_open_out:=rewrite_OK(f);
end; {two buffers seems adequate for text output files}
@#
function b_open_in(var f:byte_file):boolean;
  {open a binary file for input}
begin reset(f,name_of_file,'/B:8/O/N:2'); b_open_in:=reset_OK(f);
end;  {the \.{/B} switch is necessary to get byte packing}
@#
function b_open_out(var f:byte_file):boolean;
  {open a binary file for output}
begin rewrite(f,name_of_file,'/O/N:9/P:256'); b_open_out:=rewrite_OK(f);
end;    {here we use |ary_out| so the \.{/B} switch isn't appropriate}
  {the \.{/P:256} sets file protection to `dump never'}
@#
function w_open_in(var f:word_file):boolean;
  {open a word file for input}
begin reset(f,name_of_file,'/O/N:9'); w_open_in:=reset_OK(f);
end;
@#
function w_open_out(var f:word_file):boolean;
  {open a word file for output}
begin rewrite(f,name_of_file,'/O/N:9'); w_open_out:=rewrite_OK(f);
end;
@z

@x New input_ln: (31)
@ Input from text files is read one line at a time, using a routine called
|input_ln|. This function is defined in terms of global variables called
|buffer|, |first|, and |last| that will be described in detail later; for
now, it suffices for us to know that |buffer| is an array of |ASCII_code|
values, and that |first| and |last| are indices into this array
representing the beginning and ending of a line of text.

@<Glob...@>=
@!buffer:array[0..buf_size] of ASCII_code; {lines of characters being read}
@!first:0..buf_size; {the first unused position in |buffer|}
@!last:0..buf_size; {end of the line just input to |buffer|}
@!max_buf_stack:0..buf_size; {largest index used in |buffer|}
@y
@ Input from text files is read one line at a time, using a routine called
|input_ln|. This function is defined in terms of global variables
called |buffer|, |first|, and |last| that will be described in detail
later; for now, it suffices for us to know that |buffer| is an array of
|ASCII_code| values, and that |first| and |last| are indices into this
array representing the beginning and ending of a line of text.

We will read the lines first into an auxiliary buffer, in order to
save the running time of procedure-call overhead. This uses a nice
feature of \ph\ that Knuth chose not to mention in \TeX82.
@^Knuth, Donald Ervin@>

At {\mc SAIL} we want to recognize page marks (indicated by |form_feed|
characters), and keep track of the current page number.

@d form_feed=@'14 {ASCII code used at end of a page}

@<Glob...@>=
@!buffer:array[0..buf_size] of ASCII_code; {lines of characters being read}
@!first:0..buf_size; {the first unused position in |buffer|}
@!last:0..buf_size; {end of the line just input to |buffer|}
@!max_buf_stack:0..buf_size; {largest index used in |buffer|}
@!aux_buf:array[0..70] of text_char; {where the characters go first}
@^system dependencies@>
@z
@x
@p function input_ln(var f:alpha_file;@!bypass_eoln:boolean):boolean;
  {inputs the next line or returns |false|}
var last_nonblank:0..buf_size; {|last| with trailing blanks removed}
begin if bypass_eoln then if not eof(f) then get(f);
  {input the first character of the line into |f^|}
last:=first; {cf.\ Matthew 19\thinspace:\thinspace30}
if eof(f) then input_ln:=false
else  begin last_nonblank:=first;
  while not eoln(f) do
    begin if last>=max_buf_stack then
      begin max_buf_stack:=last+1;
      if max_buf_stack=buf_size then
        overflow("buffer size",buf_size);
@:TeX capacity exceeded buffer size}{\quad buffer size@>
      end;
    buffer[last]:=xord[f^]; get(f); incr(last);
    if buffer[last-1]<>" " then last_nonblank:=last;
    end;
  last:=last_nonblank; input_ln:=true;
  end;
end;
@y
@p function input_ln(var f:alpha_file;@!bypass_eoln:boolean):boolean;
  {inputs the next line or returns |false|}
label 1,done;
var n: integer;
@!k,@!m: 0..buf_size; {indices into |buffer|}
begin if bypass_eoln then {input the first character of the line into |f^|}
  begin if not eof(f) then get(f);
  if not eof(f) then if f^=chr(@'12) then get(f); {skip past a |line_feed|}
  end;
last:=first;
if eof(f) then input_ln:=false
else  begin read(f,aux_buf:n);
  if buffer[first]=form_feed then {previous line was end-of-page}
    begin incr(page); line:=1; {adjust line and page numbers}
    end;
1:  if last+n>max_buf_stack then
    if last+n>=buf_size then
      begin max_buf_stack:=buf_size;
      overflow("buffer size",buf_size);
@:TeX capacity exceeded buffer size}{\quad buffer size@>
      end
    else max_buf_stack:=last+n;
  if n>0 then
    begin m:=last;
    if n=72 then last:=m+71@+else last:=m+n;
    for k:=m to last-1 do buffer[k]:=xord[aux_buf[k-m]];
    if n=72 then {there's more on this line}
      begin read(f,aux_buf:n); goto 1;
      end;
    end
  else if f^=chr(form_feed) then {end of page}
    begin aux_buf[0]:=f^; n:=1; goto 1;
    end;
  loop@+  begin if last=first then goto done;
    if buffer[last-1]<>" " then goto done;
    decr(last);
    end;
done:  input_ln:=true;
  end;
end;
@^system dependencies@>
@z

@x Terminal I/O: (32)
is considered an output file the file variable is |term_out|.
@^system dependencies@>

@<Glob...@>=
@!term_in:alpha_file; {the terminal as an input file}
@!term_out:alpha_file; {the terminal as an output file}

@ Here is how to open the terminal files
in \ph. The `\.{/I}' switch suppresses the first |get|.
@^system dependencies@>

@d t_open_in==reset(term_in,'TTY:','/O/I') {open the terminal for text input}
@d t_open_out==rewrite(term_out,'TTY:','/O') {open the terminal for text output}
@y
is considered an output file the file variable is |term_out|.
On WAITS, this point is moot, since we use the built-in |TTY| file.
@^system dependencies@>

@d term_in==TTY {the terminal as an input file}
@d term_out==TTY {the terminal as an output file}

@ Here is how to open the terminal files on WAITS: we don't do anything,
since |TTY| is always open.  Note that |eoln(term_in)| is initially |true|.
@^system dependencies@>

@d t_open_in==do_nothing {open the terminal for text input}
@d t_open_out==do_nothing {open the terminal for text output}
@z

@x Special terminal controls: (34)
@d clear_terminal == break_in(term_in,true) {clear the terminal input buffer}
@d wake_up_terminal == do_nothing {cancel the user's cancellation of output}
@y
@d clear_terminal == break_in(term_in,true) {clear the terminal input buffer}
@d wake_up_terminal == begin if inskp0 then end
  {cancel the user's cancellation of output}

@<Error handling procedures@>=
function inskp0:boolean; extern;
@z

@x Initializing the terminal: (37)
@ The following program does the required initialization
without retrieving a possible command line.
It should be clear how to modify this routine to deal with command lines,
if the system permits them.
@^system dependencies@>

@p function init_terminal:boolean; {gets the terminal input started}
label exit;
begin t_open_in;
loop@+begin wake_up_terminal; write(term_out,'**'); update_terminal;
@.**@>
  if not input_ln(term_in,true) then {this shouldn't happen}
    begin write_ln(term_out);
    write(term_out,'! End of file on the terminal... why?');
@.End of file on the terminal@>
    init_terminal:=false; return;
    end;
  loc:=first;
  while (loc<last)and(buffer[loc]=" ") do incr(loc);
  if loc<last then
    begin init_terminal:=true;
    return; {return unless the line was all blank}
    end;
  write_ln(term_out,'Please type the name of your input file.');
  end;
exit:end;
@y
@ The following program does the required initialization
and accepts interrupts and also retrieves a possible command line, using
new system routines due to David R. Fuchs.
@^Fuchs, David Raymond@>

@d pto_chr(#)==ptwr1w(0,ord(#)) {put a character in the line editor}

@p procedure esci(var x:integer); extern; @t\2@>@;
  {increments |x| each time the user types escape-I or break-I;
  the program can change |x| whenever it wants to, but |x| had
  better be a global variable}
@#
function rescan:boolean; extern; @t\2@>@;
  {puts the command line into the terminal buffer,
  or returns |false| if there was no command line}
@#
function tmp_in(f:string;var s:string):integer; extern;
  @t\2@>@;
  {reads \.{TMPCOR} file |f| into |s|, and returns its length
    (|<=0| means error)}
@#
function cclsw: boolean; extern; @t\2@>@;
  {was program started with \.{RUN} offset of 1 (i.e., from \.{SNAIL})?}
@#
procedure ptwr1w(pty,c:integer); extern; @t\2@>@;
  {simulates typing of a character on a \.{PTY}}
@#
function init_terminal:boolean; {gets the terminal files started}
label exit;
var l:integer; {length returned by |tmp_in|}
@!line_found:boolean; {have we scanned a line?}
@!tmp_cor_buf:packed array[0..100] of char; {where |tmp_in| puts things}
begin t_open_in;
esci(interrupt);
last:=first;
if cclsw then {started by \.{TEX} monitor command}
  begin l:=tmp_in('TEX',tmp_cor_buf);
  loc:=1;
  while (loc<l)and(tmp_cor_buf[loc]<>':=') do incr(loc);
  incr(loc);
  while loc<l do
    begin if tmp_cor_buf[loc]>' ' then
      begin buffer[last]:=xord[tmp_cor_buf[loc]]; incr(last);
      end;
    incr(loc);
    end;
  end
else
@!debug if false then@;@+gubed@;@/
if rescan then
  begin read_ln(term_in); {get first character into |term_in^|}
  while (not eoln(term_in))and(term_in^<>';') do get(term_in);
  if term_in^=';' then
    begin get(term_in);
    while not eoln(term_in) do
      begin buffer[last]:=xord[term_in^]; incr(last); get(term_in);
      end;
    end;
  end;
line_found:=(last>first);
loop@+  begin loc:=first;
  while (loc<last)and(buffer[loc]=" ") do incr(loc);
  if loc<last then
    begin init_terminal:=true;
    return; {return unless the line was all blank}
    end;
  if line_found then
    write_ln(term_out,'Please type the name of your input file.');
  wake_up_terminal; write(term_out,'**'); update_terminal;
@.**@>
  buffer[first]:=0; {|input_ln| may look at |buffer[first]|}
  if not input_ln(term_in,true) then {this shouldn't happen}
    begin write_ln(term_out);
    write(term_out,'! End of file on the terminal... why?');
@.End of file on the terminal@>
    init_terminal:=false; return;
    end;
  line_found:=true;
  end;
exit:end;
@^system dependencies@>
@z

@x Making special characters printable: (49)
@<Character |k| cannot be printed@>=
  (k<" ")or(k>"~")
@y
@<Character |k| cannot be printed@>=
  (k=@'177)or(k in [0,@'11..@'15,@'33])
@z

@x Terminal input: (71)
begin update_terminal; {Now the user sees the prompt for sure}
@y
begin update_terminal; {Now the user sees the prompt for sure}
buffer[first]:=0; {makes sure |input_ln| doesn't find a |form_feed|}
@z

@x The `E' option: (84)
line ready to be edited. But such an extension requires some system
wizardry, so the present implementation simply types out what file should be
edited and the relevant line number.
@y
line ready to be edited. The present implementation does this by loading
the line editor with the appropriate call to the editor. We treat `\.T' the
same as `\.E', because other programs on this system invoke the editor
when the user says `\.T'.
@z
@x
"E": if base_ptr>0 then
  begin print_nl("You want to edit file ");
@.You want to edit file x@>
  print(input_stack[base_ptr].name_field);
  print(" at line "); print_int(line);
  interaction:=scroll_mode; jump_out;
  end;
@y
"E","T": if base_ptr>0 then
  begin selector:=new_string; pool_ptr:=str_start[str_ptr];
  print("et "); print(input_stack[base_ptr].name_field);
  print_char("/"); print_int(page); print("p/");
  print_int(line); print_char("l"); print_char(carriage_return);
  if str_ptr<max_strings then
    begin pseudo_typein:=str_ptr; incr(str_ptr);
    str_start[str_ptr]:=pool_ptr;
    end; {|make_string| not declared |forward|}
  selector:=term_and_log; interaction:=scroll_mode; jump_out;
  end;
@z

@x Changes for 36-bit machines: (110)
The values defined here are recommended for most 32-bit computers.

@d min_quarterword=0 {smallest allowable value in a |quarterword|}
@d max_quarterword=255 {largest allowable value in a |quarterword|}
@d min_halfword==0 {smallest allowable value in a |halfword|}
@d max_halfword==65535 {largest allowable value in a |halfword|}
@y
The values defined here are recommended for most 36-bit computers.

@d min_quarterword=0 {smallest allowable value in a |quarterword|}
@d max_quarterword=511 {largest allowable value in a |quarterword|}
@d min_halfword==0 {smallest allowable value in a |halfword|}
@d max_halfword==262143 {largest allowable value in a |halfword|}
@z

@x Eliminating addition/subtraction of zero: (112)
The inner loop of \TeX\ will run faster with respect to compilers
that don't optimize expressions like `|x+0|' and `|x-0|', if these
macros are simplified in the obvious way when |min_quarterword=0|.
@^inner loop@>@^system dependencies@>

@d qi(#)==#+min_quarterword
  {to put an |eight_bits| item into a quarterword}
@d qo(#)==#-min_quarterword
  {to take an |eight_bits| item out of a quarterword}
@d hi(#)==#+min_halfword
  {to put a sixteen-bit item into a halfword}
@d ho(#)==#-min_halfword
  {to take a sixteen-bit item from a halfword}
@y
The inner loop of \TeX\ will run faster with respect to compilers
that don't optimize expressions like `|x+0|' and `|x-0|', if these
macros are simplified in the obvious way when |min_quarterword=0|.
So they have been simplified here in the obvious way.
@^inner loop@>@^system dependencies@>

@d qi(#)==# {to put an |eight_bits| item into a quarterword}
@d qo(#)==# {to take an |eight_bits| item from a quarterword}
@d hi(#)==# {to put a sixteen-bit item into a halfword}
@d ho(#)==# {to take a sixteen-bit item from a halfword}
@z

@x Kludge to get around Pascal bug (with large array lower bounds) (116)
@!mem : array[mem_min..mem_max] of memory_word; {the big dynamic storage area}
@y
@z

@x make room for a new creation procedure [161]
\TeX's other algorithms intact.
@^system dependencies@>
@y
\TeX's other algorithms intact.
@^system dependencies@>
@p@<Declare functions needed for special kinds of nodes@>
@z

@x New command code [208-209]
@d max_non_prefixed_command=69 {largest command code that can't be \.{\\global}}

@ The next codes are special; they all relate to mode-independent
assignment of values to \TeX's internal registers or tables.
Codes that are |max_internal| or less represent internal quantities
that might be expanded by `\.{\\the}'.

@d toks_register=70 {token list register ( \.{\\toks} )}
@d assign_toks=71 {special token list ( \.{\\output}, \.{\\everypar}, etc.~)}
@d assign_int=72 {user-defined integer ( \.{\\tolerance}, \.{\\day}, etc.~)}
@d assign_dimen=73 {user-defined length ( \.{\\hsize}, etc.~)}
@d assign_glue=74 {user-defined glue ( \.{\\baselineskip}, etc.~)}
@d assign_mu_glue=75 {user-defined muglue ( \.{\\thinmuskip}, etc.~)}
@d assign_font_dimen=76 {user-defined font dimension ( \.{\\fontdimen} )}
@d assign_font_int=77 {user-defined font integer ( \.{\\hyphenchar},
  \.{\\skewchar} )}
@d set_aux=78 {specify state info ( \.{\\spacefactor}, \.{\\prevdepth} )}
@d set_prev_graf=79 {specify state info ( \.{\\prevgraf} )}
@d set_page_dimen=80 {specify state info ( \.{\\pagegoal}, etc.~)}
@d set_page_int=81 {specify state info ( \.{\\deadcycles},
  \.{\\insertpenalties} )}
@d set_box_dimen=82 {change dimension of box ( \.{\\wd}, \.{\\ht}, \.{\\dp} )}
@d set_shape=83 {specify fancy paragraph shape ( \.{\\parshape} )}
@d def_code=84 {define a character code ( \.{\\catcode}, etc.~)}
@d def_family=85 {declare math fonts ( \.{\\textfont}, etc.~)}
@d set_font=86 {set current font ( font identifiers )}
@d def_font=87 {define a font file ( \.{\\font} )}
@d register=88 {internal register ( \.{\\count}, \.{\\dimen}, etc.~)}
@d max_internal=88 {the largest code that can follow \.{\\the}}
@d advance=89 {advance a register or parameter ( \.{\\advance} )}
@d multiply=90 {multiply a register or parameter ( \.{\\multiply} )}
@d divide=91 {divide a register or parameter ( \.{\\divide} )}
@d prefix=92 {qualify a definition ( \.{\\global}, \.{\\long}, \.{\\outer} )}
@d let=93 {assign a command code ( \.{\\let}, \.{\\futurelet} )}
@d shorthand_def=94 {code definition ( \.{\\chardef}, \.{\\countdef}, etc.~)}
@d read_to_cs=95 {read into a control sequence ( \.{\\read} )}
@d def=96 {macro definition ( \.{\\def}, \.{\\gdef}, \.{\\xdef}, \.{\\edef} )}
@d set_box=97 {set a box ( \.{\\setbox} )}
@d hyph_data=98 {hyphenation data ( \.{\\hyphenation}, \.{\\patterns} )}
@d set_interaction=99 {define level of interaction ( \.{\\batchmode}, etc.~)}
@d max_command=99 {the largest command code seen at |big_switch|}
@y
@d LR=70 {text direction ( \.{\\beginL}, \.{\\beginR}, \.{\\endL}, \.{\\endR} )}
@d max_non_prefixed_command=70 {largest command code that can't be \.{\\global}}

@ The next codes are special; they all relate to mode-independent
assignment of values to \TeX's internal registers or tables.
Codes that are |max_internal| or less represent internal quantities
that might be expanded by `\.{\\the}'.

@d toks_register=71 {token list register ( \.{\\toks} )}
@d assign_toks=72 {special token list ( \.{\\output}, \.{\\everypar}, etc.~)}
@d assign_int=73 {user-defined integer ( \.{\\tolerance}, \.{\\day}, etc.~)}
@d assign_dimen=74 {user-defined length ( \.{\\hsize}, etc.~)}
@d assign_glue=75 {user-defined glue ( \.{\\baselineskip}, etc.~)}
@d assign_mu_glue=76 {user-defined muglue ( \.{\\thinmuskip}, etc.~)}
@d assign_font_dimen=77 {user-defined font dimension ( \.{\\fontdimen} )}
@d assign_font_int=78 {user-defined font integer ( \.{\\hyphenchar},
  \.{\\skewchar} )}
@d set_aux=79 {specify state info ( \.{\\spacefactor}, \.{\\prevdepth} )}
@d set_prev_graf=80 {specify state info ( \.{\\prevgraf} )}
@d set_page_dimen=81 {specify state info ( \.{\\pagegoal}, etc.~)}
@d set_page_int=82 {specify state info ( \.{\\deadcycles},
  \.{\\insertpenalties} )}
@d set_box_dimen=83 {change dimension of box ( \.{\\wd}, \.{\\ht}, \.{\\dp} )}
@d set_shape=84 {specify fancy paragraph shape ( \.{\\parshape} )}
@d def_code=85 {define a character code ( \.{\\catcode}, etc.~)}
@d def_family=86 {declare math fonts ( \.{\\textfont}, etc.~)}
@d set_font=87 {set current font ( font identifiers )}
@d def_font=88 {define a font file ( \.{\\font} )}
@d register=89 {internal register ( \.{\\count}, \.{\\dimen}, etc.~)}
@d max_internal=89 {the largest code that can follow \.{\\the}}
@d advance=90 {advance a register or parameter ( \.{\\advance} )}
@d multiply=91 {multiply a register or parameter ( \.{\\multiply} )}
@d divide=92 {divide a register or parameter ( \.{\\divide} )}
@d prefix=93 {qualify a definition ( \.{\\global}, \.{\\long}, \.{\\outer} )}
@d let=94 {assign a command code ( \.{\\let}, \.{\\futurelet} )}
@d shorthand_def=95 {code definition ( \.{\\chardef}, \.{\\countdef}, etc.~)}
@d read_to_cs=96 {read into a control sequence ( \.{\\read} )}
@d def=97 {macro definition ( \.{\\def}, \.{\\gdef}, \.{\\xdef}, \.{\\edef} )}
@d set_box=98 {set a box ( \.{\\setbox} )}
@d hyph_data=99 {hyphenation data ( \.{\\hyphenation}, \.{\\patterns} )}
@d set_interaction=100 {define level of interaction ( \.{\\batchmode}, etc.~)}
@d max_command=100 {the largest command code seen at |big_switch|}
@z

@x Special form_feed initialization: (232)
cat_code("\"):=escape; cat_code("%"):=comment;
@y
cat_code("\"):=escape; cat_code("%"):=comment;
cat_code(form_feed):=car_ret;
@z

@x Date and time: (241)
Since standard \PASCAL\ cannot provide such information, something special
is needed. The program here simply specifies July 4, 1776, at noon; but
users probably want a better approximation to the truth.

@p procedure fix_date_and_time;
begin time:=12*60; {minutes since midnight}
day:=4; {fourth day of the month}
month:=7; {seventh month of the year}
year:=1776; {Anno Domini}
end;
@y
It uses a {\mc WAITS} monitor call that puts the date in the left 18 bits
and the time in the right 18 bits.

@p procedure fix_date_and_time;
var t:integer; {accumulator}
date:integer; {raw date}
g:boolean; {garbage}
begin call_i(@'400101,,t,t,g); {that's \.{ACCTIM}}
date:=t div @'1000000;
time:=(t mod @'1000000) div 60;
day:=(date mod 31)+1;
month:=((date div 31) mod 12)+1;
year:=(date div (31*12))+1964;
end;
@z

@x Page number maintenance: (304)
If more information about the input state is needed, it can be
included in small arrays like those shown here. For example,
the current page or segment number in the input file might be
put into a variable |@!page|, maintained for enclosing levels in
`\ignorespaces|@!page_stack:array[1..max_in_open] of integer|\unskip'
by analogy with |line_stack|.
@y
Similarly, we maintain a global variable |page| and a corresponding
|page_stack|.
@z
@x
@!line_stack : array[1..max_in_open] of integer;
@y
@!line_stack : array[1..max_in_open] of integer;
@!page : integer; {current page number in the current source file}
@!page_stack : array[1..max_in_open] of integer;
@z

@x Printing the page number: (313)
else  begin print_nl("l."); print_int(line);
@y
else  begin if page>1 then
    begin print_nl("p."); print_int(page); print(",l.");
    end
  else print_nl("l.");
  print_int(line);
@z

@x More page number maintenance: (328)
or |limit| or |line|.
@y
or |limit| or |line| or |page|.
@z
@x
line_stack[index]:=line; start:=first; state:=mid_line;
@y
line_stack[index]:=line; start:=first; state:=mid_line;
page_stack[index]:=page;
@z
@x
begin first:=start; line:=line_stack[index];
@y
begin first:=start; page:=page_stack[index]; line:=line_stack[index];
@z

@x More page number printing: (336)
    print("; all text was ignored after line "); print_int(skip_line);
@y
    print("; all text was ignored after line "); print_int(skip_line);
    if skip_page>1 then
      begin print(", p."); print_int(skip_page);
      end;
@z

@x Pausing on input: (363)
@ If the user has set the |pausing| parameter to some positive value,
and if nonstop mode has not been selected, each line of input is displayed
on the terminal and the transcript file, followed by `\.{=>}'.
\TeX\ waits for a response. If the response is simply |carriage_return|, the
line is accepted as it stands, otherwise the line typed is
used instead of the line in the file.

@p procedure firm_up_the_line;
var k:0..buf_size; {an index into |buffer|}
begin limit:=last;
if pausing>0 then if interaction>nonstop_mode then
  begin wake_up_terminal; print_ln;
  if start<limit then for k:=start to limit-1 do print(buffer[k]);
  first:=limit; prompt_input("=>"); {wait for user response}
@.=>@>
  if last>first then
    begin for k:=first to last-1 do {move line down in buffer}
      buffer[k+start-first]:=buffer[k];
    limit:=start+last-first;
    end;
  end;
end;
@y
@ If the user}
@d wake_up_terminal == do_nothing {cancel the user's cancellation of output}
@y
@d clear_terminal == break_in(term_in,true) {clear the terminal input buffer}
@d wake_up_terminal == begin if inskp0 then end
  {cancel the user's cancellation of output}

@<Error handling procedures@>=
function inskp0:boolean; extern;
@z

@x Initializing the terminal: (37)
@ The following program does the required initialization
without retrieving a possible command line.
It should be clear how to modify this routine to deal with command lines,
if the system permits them.
@^system dependencies@>

@p function init_terminal:boolean; {gets the terminal input started}
label exit;
begin t_open_in;
loop@+begin wake_up_terminal; write(term_out,'**'); update_terminal;
@.**@>
  if not input_ln(term_in,true) then {this shouldn't happen}
    begin write_ln(term_out);
    write(term_out,'! End of file on the terminal... why?');
@.End of file on the terminal@>
    init_terminal:=false; return;
    end;
  loc:=first;
  while (loc<last)and(buffer[loc]=" ") do incr(loc);
  if loc<last then
    begin init_terminal:=true;
    return; {return unless the line was all blank}
    end;
  write_ln(term_out,'Please type the name of your input file.');
  end;
exit:end;
@y
@ The following program does the required initialization
and accepts interrupts and also retrieves a possible command line, using
new system routines due to David R. Fuchs.
@^Fuchs, David Raymond@>

@d pto_chr(#)==ptwr1w(0,ord(#)) {put a character in the line editor}

@p procedure esci(var x:integer); extern; @t\2@>@;
  {increments |x| each time the user types escape-I or break-I;
  the program can change |x| whenever it wants to, but |x| had
  better be a global variable}
@#
function rescan:boolean; extern; @t\2@>@;
  {puts the command line into the terminal buffer,
  or returns |false| if there was no command line}
@#
function tmp_in(f:string;var s:string):integer; extern;
  @t\2@>@;
  {reads \.{TMPCOR} file |f| into |s|, and returns its length
    (|<=0| means error)}
@#
function cclsw: boolean; extern; @t\2@>@;
  {was program started with \.{RUN} offset of 1 (i.e., from \.{SNAIL})?}
@#
procedure ptwr1w(pty,c:integer); extern; @t\2@>@;
  {simulates typing of a character on a \.{PTY}}
@#
function init_terminal:boolean; {gets the terminal files started}
label exit;
var l:integer; {length returned by |tmp_in|}
@!line_found:boolean; {have we scanned a line?}
@!tmp_cor_buf:packed array[0..100] of char; {where |tmp_in| puts things}
begin t_open_in;
esci(interrupt);
last:=first;
if cclsw then {started by \.{TEX} monitor command}
  begin l:=tmp_in('TEX',tmp_cor_buf);
  loc:=1;
  while (loc<l)and(tmp_cor_buf[loc]<>':=') do incr(loc);
  incr(loc);
  while loc<l do
    begin if tmp_cor_buf[loc]>' ' then
      begin buffer[last]:=xord[tmp_cor_buf[loc]]; incr(last);
      end;
    incr(loc);
    end;
  end
else
@!debug if false then@;@+gubed@;@/
if rescan then
  begin read_ln(term_in); {get first character into |term_in^|}
  while (not eoln(term_in))and(term_in^<>';') do get(term_in);
  if term_in^=';' then
    begin get(term_in);
    while not eoln(term_in) do
      begin buffer[last]:=xord[term_in^]; incr(last); get(term_in);
      end;
    end;
  end;
line_found:=(last>first);
loop@+  begin loc:=first;
  while (loc<last)and(buffer[loc]=" ") do incr(loc);
  if loc<last then
    begin init_terminal:=true;
    return; {return unless the line was all blank}
    end;
  if line_found then
    write_ln(term_out,'Please type the name of your input file.');
  wake_up_terminal; write(term_out,'**'); update_terminal;
@.**@>
  buffer[first]:=0; {|input_ln| may look at |buffer[first]|}
  if not input_ln(term_in,true) then {this shouldn't happen}
    begin write_ln(term_out);
    write(term_out,'! End of file on the terminal... why?');
@.End of file on the terminal@>
    init_terminal:=false; return;
    end;
  line_found:=true;
  end;
exit:end;
@^system dependencies@>
@z

@x Making special characters printable: (49)
@<Character |k| cannot be printed@>=
  (k<" ")or(k>"~")
@y
@<Character |k| cannot be printed@>=
  (k=@'177)or(k in [0,@'11..@'15,@'33])
@z

@x Terminal input: (71)
begin update_terminal; {Now the user sees the prompt for sure}
@y
begin update_terminal; {Now the user sees the prompt for sure}
buffer[first]:=0; {makes sure |input_ln| doesn't find a |form_feed|}
@z

@x The `E' option: (84)
line ready to be edited. But such an extension requires some system
wizardry, so the present implementation simply types out what file should be
edited and the relevant line number.
@y
line ready to be edited. The present implementation does this by loading
the line editor with the appropriate call to the editor. We treat `\.T' the
same as `\.E', because other programs on this system invoke the editor
when the user says `\.T'.
@z
@x
"E": if base_ptr>0 then
  begin print_nl("You want to edit file ");
@.You want to edit file x@>
  print(input_stack[base_ptr].name_field);
  print(" at line "); print_int(line);
  interaction:=scroll_mode; jump_out;
  end;
@y
"E","T": if base_ptr>0 then
  begin selector:=new_string; pool_ptr:=str_start[str_ptr];
  print("et "); print(input_stack[base_ptr].name_field);
  print_char("/"); print_int(page); print("p/");
  print_int(line); print_char("l"); print_char(carriage_return);
  if str_ptr<max_strings then
    begin pseudo_typein:=str_ptr; incr(str_ptr);
    str_start[str_ptr]:=pool_ptr;
    end; {|make_string| not declared |forward|}
  selector:=term_and_log; interaction:=scroll_mode; jump_out;
  end;
@z

@x Changes for 36-bit machines: (110)
The values defined here are recommended for most 32-bit computers.

@d min_quarterword=0 {smallest allowable value in a |quarterword|}
@d max_quarterword=255 {largest allowable value in a |quarterword|}
@d min_halfword==0 {smallest allowable value in a |halfword|}
@d max_halfword==65535 {largest allowable value in a |halfword|}
@y
The values defined here are recommended for most 36-bit computers.

@d min_quarterword=0 {smallest allowable value in a |quarterword|}
@d max_quarterword=511 {largest allowable value in a |quarterword|}
@d min_halfword==0 {smallest allowable value in a |halfword|}
@d max_halfword==262143 {largest allowable value in a |halfword|}
@z

@x Eliminating addition/subtraction of zero: (112)
The inner loop of \TeX\ will run faster with respect to compilers
that don't optimize expressions like `|x+0|' and `|x-0|', if these
macros are simplified in the obvious way when |min_quarterword=0|.
@^inner loop@>@^system dependencies@>

@d qi(#)==#+min_quarterword
  {to put an |eight_bits| item into a quarterword}
@d qo(#)==#-min_quarterword
  {to take an |eight_bits| item out of a quarterword}
@d hi(#)==#+min_halfword
  {to put a sixteen-bit item into a halfword}
@d ho(#)==#-min_halfword
  {to take a sixteen-bit item from a halfword}
@y
The inner loop of \TeX\ will run faster with respect to compilers
that don't optimize expressions like `|x+0|' and `|x-0|', if these
macros are simplified in the obvious way when |min_quarterword=0|.
So they have been simplified here in the obvious way.
@^inner loop@>@^system dependencies@>

@d qi(#)==# {to put an |eight_bits| item into a quarterword}
@d qo(#)==# {to take an |eight_bits| item from a quarterword}
@d hi(#)==# {to put a sixteen-bit item into a halfword}
@d ho(#)==# {to take a sixteen-bit item from a halfword}
@z

@x Kludge to get around Pascal bug (with large array lower bounds) (116)
@!mem : array[mem_min..mem_max] of memory_word; {the big dynamic storage area}
@y
@z

@x make room for a new creation procedure [161]
\TeX's other algorithms intact.
@^system dependencies@>
@y
\TeX's other algorithms intact.
@^system dependencies@>
@p@<Declare functions needed for special kinds of nodes@>
@z

@x New command code [208-209]
@d max_non_prefixed_command=69 {largest command code that can't be \.{\\global}}

@ The next codes are special; they all relate to mode-independent
assignment of values to \TeX's internal registers or tables.
Codes that are |max_internal| or less represent internal quantities
that might be expanded by `\.{\\the}'.

@d toks_register=70 {token list register ( \.{\\toks} )}
@d assign_toks=71 {special token list ( \.{\\output}, \.{\\everypar}, etc.~)}
@d assign_int=72 {user-defined integer ( \.{\\tolerance}, \.{\\day}, etc.~)}
@d assign_dimen=73 {user-defined length ( \.{\\hsize}, etc.~)}
@d assign_glue=74 {user-defined glue ( \.{\\baselineskip}, etc.~)}
@d assign_mu_glue=75 {user-defined muglue ( \.{\\thinmuskip}, etc.~)}
@d assign_font_dimen=76 {user-defined font dimension ( \.{\\fontdimen} )}
@d assign_font_int=77 {user-defined font integer ( \.{\\hyphenchar},
  \.{\\skewchar} )}
@d set_aux=78 {specify state info ( \.{\\spacefactor}, \.{\\prevdepth} )}
@d set_prev_graf=79 {specify state info ( \.{\\prevgraf} )}
@d set_page_dimen=80 {specify state info ( \.{\\pagegoal}, etc.~)}
@d set_page_int=81 {specify state info ( \.{\\deadcycles},
  \.{\\insertpenalties} )}
@d set_box_dimen=82 {change dimension of box ( \.{\\wd}, \.{\\ht}, \.{\\dp} )}
@d set_shape=83 {specify fancy paragraph shape ( \.{\\parshape} )}
@d def_code=84 {define a character code ( \.{\\catcode}, etc.~)}
@d def_family=85 {declare math fonts ( \.{\\textfont}, etc.~)}
@d set_font=86 {set current font ( font identifiers )}
@d def_font=87 {define a font file ( \.{\\font} )}
@d register=88 {internal register ( \.{\\count}, \.{\\dimen}, etc.~)}
@d max_internal=88 {the largest code that can follow \.{\\the}}
@d advance=89 {advance a register or parameter ( \.{\\advance} )}
@d multiply=90 {multiply a register or parameter ( \.{\\multiply} )}
@d divide=91 {divide a register or parameter ( \.{\\divide} )}
@d prefix=92 {qualify a definition ( \.{\\global}, \.{\\long}, \.{\\outer} )}
@d let=93 {assign a command code ( \.{\\let}, \.{\\futurelet} )}
@d shorthand_def=94 {code definition ( \.{\\chardef}, \.{\\countdef}, etc.~)}
@d read_to_cs=95 {read into a control sequence ( \.{\\read} )}
@d def=96 {macro definition ( \.{\\def}, \.{\\gdef}, \.{\\xdef}, \.{\\edef} )}
@d set_box=97 {set a box ( \.{\\setbox} )}
@d hyph_data=98 {hyphenation data ( \.{\\hyphenation}, \.{\\patterns} )}
@d set_interaction=99 {define level of interaction ( \.{\\batchmode}, etc.~)}
@d max_command=99 {the largest command code seen at |big_switch|}
@y
@d LR=70 {text direction ( \.{\\beginL}, \.{\\beginR}, \.{\\endL}, \.{\\endR} )}
@d max_non_prefixed_command=70 {largest command code that can't be \.{\\global}}

@ The next codes are special; they all relate to mode-independent
assignment of values to \TeX's internal registers or tables.
Codes that are |max_internal| or less represent internal quantities
that might be expanded by `\.{\\the}'.

@d toks_register=71 {token list register ( \.{\\toks} )}
@d assign_toks=72 {special token list ( \.{\\output}, \.{\\everypar}, etc.~)}
@d assign_int=73 {user-defined integer ( \.{\\tolerance}, \.{\\day}, etc.~)}
@d assign_dimen=74 {user-defined length ( \.{\\hsize}, etc.~)}
@d assign_glue=75 {user-defined glue ( \.{\\baselineskip}, etc.~)}
@d assign_mu_glue=76 {user-defined muglue ( \.{\\thinmuskip}, etc.~)}
@d assign_font_dimen=77 {user-defined font dimension ( \.{\\fontdimen} )}
@d assign_font_int=78 {user-defined font integer ( \.{\\hyphenchar},
  \.{\\skewchar} )}
@d set_aux=79 {specify state info ( \.{\\spacefactor}, \.{\\prevdepth} )}
@d set_prev_graf=80 {specify state info ( \.{\\prevgraf} )}
@d set_page_dimen=81 {specify state info ( \.{\\pagegoal}, etc.~)}
@d set_page_int=82 {specify state info ( \.{\\deadcycles},
  \.{\\insertpenalties} )}
@d set_box_dimen=83 {change dimension of box ( \.{\\wd}, \.{\\ht}, \.{\\dp} )}
@d set_shape=84 {specify fancy paragraph shape ( \.{\\parshape} )}
@d def_code=85 {define a character code ( \.{\\catcode}, etc.~)}
@d def_family=86 {declare math fonts ( \.{\\textfont}, etc.~)}
@d set_font=87 {set current font ( font identifiers )}
@d def_font=88 {define a font file ( \.{\\font} )}
@d register=89 {internal register ( \.{\\count}, \.{\\dimen}, etc.~)}
@d max_internal=89 {the largest code that can follow \.{\\the}}
@d advance=90 {advance a register or parameter ( \.{\\advance} )}
@d multiply=91 {multiply a register or parameter ( \.{\\multiply} )}
@d divide=92 {divide a register or parameter ( \.{\\divide} )}
@d prefix=93 {qualify a definition ( \.{\\global}, \.{\\long}, \.{\\outer} )}
@d let=94 {assign a command code ( \.{\\let}, \.{\\futurelet} )}
@d shorthand_def=95 {code definition ( \.{\\chardef}, \.{\\countdef}, etc.~)}
@d read_to_cs=96 {read into a control sequence ( \.{\\read} )}
@d def=97 {macro definition ( \.{\\def}, \.{\\gdef}, \.{\\xdef}, \.{\\edef} )}
@d set_box=98 {set a box ( \.{\\setbox} )}
@d hyph_data=99 {hyphenation data ( \.{\\hyphenation}, \.{\\patterns} )}
@d set_interaction=100 {define level of interaction ( \.{\\batchmode}, etc.~)}
@d max_command=100 {the largest command code seen at |big_switch|}
@z

@x Special form_feed initialization: (232)
cat_code("\"):=escape; cat_code("%"):=comment;
@y
cat_code("\"):=escape; cat_code("%"):=comment;
cat_code(form_feed):=car_ret;
@z

@x Date and time: (241)
Since standard \PASCAL\ cannot provide such information, something special
is needed. The program here simply specifies July 4, 1776, at noon; but
users probably want a better approximation to the truth.

@p procedure fix_date_and_time;
begin time:=12*60; {minutes since midnight}
day:=4; {fourth day of the month}
month:=7; {seventh month of the year}
year:=1776; {Anno Domini}
end;
@y
It uses a {\mc WAITS} monitor call that puts the date in the left 18 bits
and the time in the right 18 bits.

@p procedure fix_date_and_time;
var t:integer; {accumulator}
date:integer; {raw date}
g:boolean; {garbage}
begin call_i(@'400101,,t,t,g); {that's \.{ACCTIM}}
date:=t div @'1000000;
time:=(t mod @'1000000) div 60;
day:=(date mod 31)+1;
month:=((date div 31) mod 12)+1;
year:=(date div (31*12))+1964;
end;
@z

@x Page number maintenance: (304)
If more information about the input state is needed, it can be
included in small arrays like those shown here. For example,
the current page or segment number in the input file might be
put into a variable |@!page|, maintained for enclosing levels in
`\ignorespaces|@!page_stack:array[1..max_in_open] of integer|\unskip'
by analogy with |line_stack|.
@y
Similarly, we maintain a global variable |page| and a corresponding
|page_stack|.
@z
@x
@!line_stack : array[1..max_in_open] of integer;
@y
@!line_stack : array[1..max_in_open] of integer;
@!page : integer; {current page number in the current source file}
@!page_stack : array[1..max_in_open] of integer;
@z

@x Printing the page number: (313)
else  begin print_nl("l."); print_int(line);
@y
else  begin if page>1 then
    begin print_nl("p."); print_int(page); print(",l.");
    end
  else print_nl("l.");
  print_int(line);
@z

@x More page number maintenance: (328)
or |limit| or |line|.
@y
or |limit| or |line| or |page|.
@z
@x
line_stack[index]:=line; start:=first; state:=mid_line;
@y
line_stack[index]:=line; start:=first; state:=mid_line;
page_stack[index]:=page;
@z
@x
begin first:=start; line:=line_stack[index];
@y
begin first:=start; page:=page_stack[index]; line:=line_stack[index];
@z

@x More page number printing: (336)
    print("; all text was ignored after line "); print_int(skip_line);
@y
    print("; all text was ignored after line "); print_int(skip_line);
    if skip_page>1 then
      begin print(", p."); print_int(skip_page);
      end;
@z

@x Pausing on input: (363)
@ If the user has set the |pausing| parameter to some positive value,
and if nonstop mode has not been selected, each line of input is displayed
on the terminal and the transcript file, followed by `\.{=>}'.
\TeX\ waits for a response. If the response is simply |carriage_return|, the
line is accepted as it stands, otherwise the line typed is
used instead of the line in the file.

@p procedure firm_up_the_line;
var k:0..buf_size; {an index into |buffer|}
begin limit:=last;
if pausing>0 then if interaction>nonstop_mode then
  begin wake_up_terminal; print_ln;
  if start<limit then for k:=start to limit-1 do print(buffer[k]);
  first:=limit; prompt_input("=>"); {wait for user response}
@.=>@>
  if last>first then
    begin for k:=first to last-1 do {move line down in buffer}
      buffer[k+start-first]:=buffer[k];
    limit:=start+last-first;
    end;
  end;
end;
@y
@ If the user has set the |pausing| parameter to some positive value,
and if nonstop mode has not been selected,
each line of input is displayed in the transcript file, followed by `\.{=>}',
and also put into the user's line-editor buffer.
\TeX\ waits for the line to be edited, and the next line received is
used instead of the line in the file.

@p procedure firm_up_the_line;
var k:0..buf_size; {an index into |buffer|}
begin limit:=last;
if pausing>0 then if interaction>nonstop_mode then
 if buffer[start]<>form_feed then
  begin wake_up_terminal; print_ln;
  if start=limit then {empty line will be made nonempty so that it's visible}
    begin buffer[start]:=" "; incr(limit);
    end;
  decr(selector); {inhibit terminal output temporarily}
  for k:=start to limit-1 do
    begin print_char(buffer[k]);
    pto_chr(xchr[buffer[k]]);
    end;
  print("=>"); first:=start;
  if not input_ln(term_in,true) then
    fatal_error("End of file on the terminal!");
@.End of file on the terminal@>
  if last>first then for k:=first to last-1 do print_char(buffer[k]);
  limit:=last; print_ln; incr(selector);
  end;
end;
@z

@x Reading the first line of a file: (485)
@ The first line of a file must be treated specially, since |input_ln|
must be told not to start with |get|.
@^system dependencies@>

@<Input the first line of |read_file[m]|@>=
if input_ln(read_file[m],false) then read_open[m]:=normal
else  begin a_close(read_file[m]); read_open[m]:=closed;
  end
@y
@ The first line of a file must be treated specially, since |input_ln|
must be told not to |get|. Furthermore we want to omit the optional file
directory page present at {\mc SAIL}.
@^system dependencies@>

@<Input the first line of |read_file[m]|@>=
if not input_ln(read_file[m],false) then
  begin a_close(read_file[m]); read_open[m]:=closed;
  end
else  begin
  if(last-start=29)and(buffer[start]="C")and(buffer[start+8]=@'26) then
    begin while (read_file[m]^<>chr(form_feed))and(not eof(read_file[m])) do
      begin read_ln(read_file[m]); read(read_file[m],aux_buf:temp_ptr);
      end; {skip the directory}
    buffer[start]:=form_feed; last:=start+1;
    end;
  read_open[m]:=normal;
  end
@z

@x Still more page number maintenance: (493)
where skipping began, for use in error messages.

@<Glob...@>=
@!skip_line:integer; {skipping began here}
@y
where skipping began, for use in error messages. Also the page number.

@<Glob...@>=
@!skip_line,@!skip_page:integer; {skipping began here}
@z
@x
skip_line:=line;
@y
skip_line:=line; skip_page:=page;
@z

@x Parsing file names: (513)
@ The file names we shall deal with for illustrative purposes have the
following structure:  If the name contains `\.>' or `\.:', the file area
consists of all characters up to and including the final such character;
otherwise the file area is null.  If the remaining file name contains
`\..', the file extension consists of all such characters from the first
remaining `\..' to the end, otherwise the file extension is null.
@^system dependencies@>

We can scan such file names easily by using two global variables that keep track
of the occurrences of area and extension delimiters:

@<Glob...@>=
@!area_delimiter:pool_pointer; {the most recent `\.>' or `\.:', if any}
@!ext_delimiter:pool_pointer; {the relevant `\..', if any}
@y
@ The file names we shall deal with have the following structure:
If the name contains `\.[', the file area consists of all characters
from this character to the end; otherwise the file area is null.
If the remaining file name contains `\..', the file extension consists of all
such characters from this character to the end, otherwise the file extension
is null. We can assume that there is at most one `\.[' and at most one `\..'.
@^system dependencies@>

We can scan such file names easily by using two global variables that keep track
of the occurrences of area and extension delimiters:

@<Glob...@>=
@!area_delimiter:pool_pointer; {the most recent `\.[', if any}
@!ext_delimiter:pool_pointer; {the relevant `\..', if any}
@z
@x
@d TEX_area=="TeXinputs:"
@.TeXinputs@>
@d TEX_font_area=="TeXfonts:"
@.TeXfonts@>
@y
@d TEX_area=="[tex,sys]"
@d TEX_font_area=="[tfm,sys]"
@z
@x
else  begin if (c=">")or(c=":") then
    begin area_delimiter:=pool_ptr; ext_delimiter:=0;
    end
  else if (c=".")and(ext_delimiter=0) then ext_delimiter:=pool_ptr;
@y
else  begin if c="[" then area_delimiter:=pool_ptr
  else if c="." then ext_delimiter:=pool_ptr;
@z
@x
if area_delimiter=0 then cur_area:=""
else  begin cur_area:=str_ptr; incr(str_ptr);
  str_start[str_ptr]:=area_delimiter+1;
  end;
if ext_delimiter=0 then
  begin cur_ext:=""; cur_name:=make_string;
  end
else  begin cur_name:=str_ptr; incr(str_ptr);
  str_start[str_ptr]:=ext_delimiter; cur_ext:=make_string;
  end;
@y
cur_name:=str_ptr;
if ext_delimiter=0 then cur_ext:=""
else  begin incr(str_ptr);
  str_start[str_ptr]:=ext_delimiter; cur_ext:=str_ptr;
  end;
if area_delimiter<=str_start[str_ptr] then
  begin cur_area:=""; incr(str_ptr); str_start[str_ptr]:=pool_ptr;
  end
else  begin incr(str_ptr);
  str_start[str_ptr]:=area_delimiter; cur_area:=make_string;
  end;
@z

@x Printing file names: (518)
begin print(a); print(n); print(e);
@y
begin print(n); print(e); print(a);
@z

@x Converting file names to Pascal strings: (519)
allows both lowercase and uppercase letters in the file name.
@^system dependencies@>

@d append_to_name(#)==begin c:=#; incr(k);
@y
converts lowercase letters to uppercase.

A special convention is used here with respect to font metric files: If the
file name is longer than six characters (e.g., `\.{helvetica}' or
`\.{oldenglish}'), we abbreviate it by retaining the first three and
last three characters (e.g., `\.{helica}' or `\.{oldish}').
@^system dependencies@>

@d append_to_name(#)==begin c:=#; incr(k);
  if (c>="a")and(c<="z") then c:=c-@'40; {convert to uppercase}
@z
@x
for j:=str_start[a] to str_start[a+1]-1 do append_to_name(str_pool[j]);
for j:=str_start[n] to str_start[n+1]-1 do append_to_name(str_pool[j]);
for j:=str_start[e] to str_start[e+1]-1 do append_to_name(str_pool[j]);
@y
if (e=".tfm")and(length(n)>6) then
  begin for j:=str_start[n] to str_start[n]+2 do
    append_to_name(str_pool[j]);
  for j:=str_start[n+1]-3 to str_start[n+1]-1 do
    append_to_name(str_pool[j]);
  end
else for j:=str_start[n] to str_start[n+1]-1 do append_to_name(str_pool[j]);
for j:=str_start[e] to str_start[e+1]-1 do append_to_name(str_pool[j]);
for j:=str_start[a] to str_start[a+1]-1 do append_to_name(str_pool[j]);
@z

@x Parsing file names in the buffer: (520)
@d format_default_length=20 {length of the |TEX_format_default| string}
@d format_area_length=11 {length of its area part}
@d format_ext_length=4 {length of its `\.{.fmt}' part}
@y
@d format_default_length=18 {length of the |TEX_format_default| string}
@d format_area_length=9 {length of its area part}
@d format_ext_length=4 {length of its `\.{.fmt}' part}
@z
@x
TEX_format_default:='TeXformats:plain.fmt';
@.TeXformats@>
@y
TEX_format_default:='plain.fmt[tex,sys]';
@z
@x
|TEX_format_default|.
@y
|TEX_format_default|; but it actually switches stuff around to keep the
file area last.
@z
@x
@!j:integer; {index into |buffer| or |TEX_format_default|}
@y
@!j:integer; {index into |buffer| or |TEX_format_default|}
@!d:integer; {a kludge}
@z
@x
for j:=1 to n do append_to_name(xord[TEX_format_default[j]]);
for j:=a to b do append_to_name(buffer[j]);
for j:=format_default_length-format_ext_length+1 to format_default_length do
  append_to_name(xord[TEX_format_default[j]]);
@y
for j:=a to b do append_to_name(buffer[j]);
if b=0 then
  begin d:=format_default_length-format_area_length+1;
  n:=format_default_length;
  end
else d:=format_default_length-format_area_length-format_ext_length+1;
for j:=d to format_default_length-format_area_length do
  append_to_name(xord[TEX_format_default[j]]);
for j:=format_default_length-n+1 to format_default_length do
  append_to_name(xord[TEX_format_default[j]]);
@z

@x The real file names: (525)
@ Operating systems often make it possible to determine the exact name (and
possible version number) of a file that has been opened. The following routine,
which simply makes a \TeX\ string from the value of |name_of_file|, should
ideally be changed to deduce the full name of file~|f|, which is the file
most recently opened, if it is possible to do this in a \PASCAL\ program.
@^system dependencies@>

This routine might be called after string memory has overflowed, hence
we dare not use `|str_room|'.

@p function make_name_string:str_number;
var k:1..file_name_size; {index into |name_of_file|}
begin if (pool_ptr+name_length>pool_size)or(str_ptr=max_strings) then
  make_name_string:="?"
else  begin for k:=1 to name_length do append_char(xord[name_of_file[k]]);
  make_name_string:=make_string;
  end;
end;
function a_make_name_string(var f:alpha_file):str_number;
begin a_make_name_string:=make_name_string;
end;
function b_make_name_string(var f:byte_file):str_number;
begin b_make_name_string:=make_name_string;
end;
function w_make_name_string(var f:word_file):str_number;
begin w_make_name_string:=make_name_string;
end;
@y
@ Operating systems often make it possible to determine the exact name (and
possible version number) of a file that has been opened. The following routine,
due to David Fuchs, deduces the full name of file~|f| on {\mc WAITS}:
@^system dependencies@>
@^Fuchs, David Raymond@>

@p procedure cur_nam(var chan:f@&i@&l@&e;var s:string); extern; @t\2@>@/
function make_name_string(var f:f@&i@&l@&e):str_number;
var s:packed array[1..24] of char;
@!k:1..24; {file names at {\sc SAIL} have at most 23 characters}
begin if (pool_ptr+24>pool_size)or(str_ptr=max_strings) then
  make_name_string:="?"
else  begin cur_nam(f,s); k:=1;
  while ord(s[k])<>0 do
    begin append_char(xord[s[k]]); incr(k);
    end;
  make_name_string:=make_string;
  end;
end;
function a_make_name_string(var f:alpha_file):str_number;
begin a_make_name_string:=make_name_string(f);
end;
function b_make_name_string(var f:byte_file):str_number;
begin b_make_name_string:=make_name_string(f);
end;
function w_make_name_string(var f:word_file):str_number;
begin w_make_name_string:=make_name_string(f);
end;
@z

@x Line editor gets misspelled file name: (530)
begin if interaction=scroll_mode then wake_up_terminal;
@y
@!i:pool_pointer; {index into |str_pool|}
begin if interaction=scroll_mode then wake_up_terminal;
@z
@x
clear_terminal; prompt_input(": "); @<Scan file name in the buffer@>;
@y
clear_terminal; {now we'll fill the line editor's buffer with the old name}
for i:=str_start[cur_name] to str_start[cur_name+1]-1 do
  pto_chr(xchr[str_pool[i]]);
for i:=str_start[cur_ext] to str_start[cur_ext+1]-1 do
  pto_chr(xchr[str_pool[i]]);
for i:=str_start[cur_area] to str_start[cur_area+1]-1 do
  pto_chr(xchr[str_pool[i]]);
ptwr1w(0,@'214); {control-formfeed returns cursor to start of line}
prompt_input(": "); @<Scan file name in the buffer@>;
@z

@x Reading the first line of a file, again: (538)
@ Here we have to remember to tell the |input_ln| routine not to
start with a |get|. If the file is empty, it is considered to
contain a single blank line.
@^system dependencies@>
@^empty line at end of file@>

@<Read the first line...@>=
begin if not input_ln(cur_file,false) then do_nothing;
@y
@ Here we have to remember to tell |input_ln| not to do the first |get|,
and we also want to skip over a file directory page. An empty file
is considered to contain a single blank line.
@^system dependencies@>
@^empty line at end of file@>

@<Read the first line...@>=
begin if input_ln(cur_file,false) then
  begin if(last-start=29)and(buffer[start]="C")and(buffer[start+8]=@'26) then
    begin while (cur_file^<>chr(form_feed))and(not eof(cur_file)) do
      begin read_ln(cur_file); read(cur_file,aux_buf:temp_ptr);
      end; {skip the directory}
    buffer[start]:=form_feed; last:=start+1;
    end;
  end;
page:=1;
@z

@x new DVI opcodes [585-586]
\yskip\noindent Commands 250--255 are undefined at the present time.

@ @d set_char_0=0 {typeset character 0 and move right}
@y
\yskip\hang|begin_reflect| 250. Begin a (possibly recursive) reflected segment.

\yskip\hang|end_reflect| 251. End a (possibly recursive) reflected segment.

\yskip\noindent Commands 250--255 are undefined in normal \.{DVI} files,
but 250 and 251 are permitted in the special `\.{DVI-IVD}' files
produced by this variant of \TeX.

@ @d begin_reflect=250 {begin a reflected segment (not normally allowed)}
@d end_reflect=251 {end a reflected segment (not normally allowed)}
@d set_char_0=0 {typeset character 0 and move right}
@z

@x The DVI output buffer: (594)
@!dvi_index=0..dvi_buf_size; {an index into the output buffer}
@y
@!dvi_index=0..dvi_buf_size; {an index into the output buffer}
@!packed_bytes=packed array[dvi_index] of eight_bits;
  {buffer for \.{DVI} output}
@z
@x
@!dvi_buf:array[dvi_index] of eight_bits; {buffer for \.{DVI} output}
@y
@!dvi_buf:packed_bytes; {buffer for \.{DVI} output}
@z
@x
@p procedure write_dvi(@!a,@!b:dvi_index);
var k:dvi_index;
begin for k:=a to b do write(dvi_file,dvi_buf[k]);
end;
@y
@p procedure ary_out(var f:file;@!b:packed_bytes; @!o,@!c:integer);
  extern;@t\2@>@#
procedure write_dvi(@!a,@!b:dvi_index);
begin ary_out(dvi_file,dvi_buf,a div 4,(b+1-a)div 4);
end;
@z

@x changes to ship_out [638]
begin if tracing_output>0 then
@y
begin LR_ptr:=get_avail; info(LR_ptr):=0; {|begin_L_code| at outer level}
if tracing_output>0 then
@z
@x (module 639)
flush_node_list(p);
@y
flush_node_list(p); @<Flush the LR stack@>;
@z

@x "r DVIdover": (642)
  b_close(dvi_file);
@y
  b_close(dvi_file);
  if pseudo_typein=0 then
    begin k:=selector; selector:=new_string;
    pool_ptr:=str_start[str_ptr];
    print("r DVIdover;"); print(output_file_name);
    selector:=k;
    if pool_ptr<pool_size then
     if str_ptr<max_strings then {|overflow| can't occur}
      pseudo_typein:=make_string;
    end;
@z

@x hpack changes [649]
begin r:=get_node(box_node_size); type(r):=hlist_node;
@y
@!LR_ptr,@!LR_tmp:pointer; {for LR stack maintenance}
@!LR_problems:integer; {counts missing begins and ends}
begin LR_ptr:=null; LR_problems:=0;
r:=get_node(box_node_size); type(r):=hlist_node;
@z
@x (module 649, continued)
exit: hpack:=r;
@y
exit: @<Check for LR anomalies at the end of |hpack|@>;
hpack:=r;
@z

@x Page numbers on over/underfull box messages: (663)
  print_int(line);
@y
  print_int(line);
  if page>1 then
    begin print(", p."); print_int(page);
    end;
@z
@x
  print_int(line);
@y
  print_int(line);
  if page>1 then
    begin print(", p."); print_int(page);
    end;
@z

@x post_line_break stuff [877]
begin @<Reverse the links of the relevant passive nodes, setting |cur_p| to the
@y
@!LR_ptr,@!LR_tmp:pointer; {for LR stack maintenance}
begin LR_ptr:=null;
 @<Reverse the links of the relevant passive nodes, setting |cur_p| to the
@z
@x (module 877, continued)
prev_graf:=best_line-1;
@y
prev_graf:=best_line-1;
@<Flush the LR stack@>;
@z
@x (module 880)
@<Modify the end of the line to reflect the nature of the break and to include
  \.{\\rightskip}; also set the proper value of |disc_break|@>;
@y
@<Insert LR nodes at the beginning of the current line@>;
@<Adjust the LR stack based on LR nodes in this line@>;
@<Modify the end of the line to reflect the nature of the break and to include
  \.{\\rightskip}; also set the proper value of |disc_break|@>;
@<Insert LR nodes at the end of the current line@>;
@z

@x new horizontal command [1090]
   vmode+ex_space:@t@>@;@/
@y
   vmode+ex_space,vmode+LR:@t@>@;@/
@z

@x math in text is L-text [module 1196]
begin tail_append(new_math(math_surround,before));
@y
begin tail_append(new_math(math_surround,before));
@<Append a |begin_L| to the tail of the current list@>;
@z
@x (module 1196, continued)
tail_append(new_math(math_surround,after));
@y
@<Append an |end_L| to the tail of the current list@>;
tail_append(new_math(math_surround,after));
@z

@x The endgame: (1335)
@<Last-minute...@>=
@y
The new stuff at {\mc SAIL} has to do with preparing for what the user
presumably wants to do next, by typing it for him/her.

@<Last-minute...@>=
@z
@x
end;
@y
if (pseudo_typein<>0)and(interaction>batch_mode) then
  begin write_ln(term_out);
  for k:=str_start[pseudo_typein] to str_start[pseudo_typein+1]-1 do
    pto_chr(xchr[str_pool[k]]);
  end;
end;
@z

@x whatsit processing [1341]
@d special_node=3 {|subtype| in whatsits that represent \.{\\special} things}
@y
@d special_node=3 {|subtype| in whatsits that represent \.{\\special} things}
@d LR_node=4 {|subtype| in whatsits that represent \.{\\beginL}, etc.}
@d LR_type(#)==mem[#+1].int {the sub-subtype}
@z
@x (module 1344)
@d immediate_code=4 {command modifier for \.{\\immediate}}

@<Put each...@>=
@y
@d immediate_code=4 {command modifier for \.{\\immediate}}
@d begin_L_code=0 {command modifier for \.{\\beginL}}
@d begin_R_code=1 {command modifier for \.{\\beginR}}
@d end_L_code=2 {command modifier for \.{\\endL}}
@d end_R_code=3 {command modifier for \.{\\endR}}
@d begin_LR(#)==(LR_type(#)<end_L_code)
@d begin_LR_type(#)==(LR_type(#)-end_L_code)

@<Put each...@>=
primitive("beginL",LR,begin_L_code);@/
@!@:begin_L_}{\.{\\beginL} primitive@>
primitive("beginR",LR,begin_R_code);@/
@!@:begin_R_}{\.{\\beginR} primitive@>
primitive("endL",LR,end_L_code);@/
@!@:end_L_}{\.{\\endL} primitive@>
primitive("endR",LR,end_R_code);@/
@!@:end_R_}{\.{\\endR} primitive@>
@z
@x (module 1346)
@ @<Cases of |print_cmd_chr|...@>=
@y
@ @<Cases of |print_cmd_chr|...@>=
LR: case chr_code of
begin_L_code: print_esc("beginL");
begin_R_code: print_esc("beginR");
end_L_code: print_esc("endL");
othercases print_esc("endR")
endcases;
@z
@x (module 1356)
othercases print("whatsit?")
@y
LR_node: case LR_type(p) of
begin_L_code: print_esc("beginL");
begin_R_code: print_esc("beginR");
end_L_code: print_esc("endL");
othercases print_esc("endR")
endcases;
othercases print("whatsit?")
@z
@x (module 1357)
close_node: begin r:=get_node(small_node_size); words:=small_node_size;
@y
close_node,LR_node: begin r:=get_node(small_node_size); words:=small_node_size;
@z
@x (module 1358)
close_node: free_node(p,small_node_size);
@y
close_node,LR_node: free_node(p,small_node_size);
@z
@x (module 1360)
@ @<Incorporate a whatsit node into an hbox@>=do_nothing
@y
@ @<Incorporate a whatsit node into an hbox@>=
if subtype(p)=LR_node then @<Adjust the LR stack for the |hpack| routine@>
@z
@x (module 1366)
@ @<Output the whatsit node |p| in an hlist@>=
out_what(p)
@y
@ @<Output the whatsit node |p| in an hlist@>=
if subtype(p)<>LR_node then out_what(p)
else @<Output a reflection instruction if the direction has changed@>
@z

@x Final system-dependent changes: [1376]
This section should be replaced, if necessary, by changes to the program
that are necessary to make \TeX\ work at a particular installation.
It is usually best to design your change file so that all changes to
previous sections preserve the section numbering; then everybody's version
will be consistent with the published program. More extensive changes,
which introduce new sections, can be inserted here; then only the index
itself will get a new section number.
@^system dependencies@>
@y
Now we do the main work required for mixed-direction texts.

@<Cases of |main_control| that build...@>=
hmode+LR: begin new_whatsit(LR_node,small_node_size); LR_type(tail):=cur_chr;
  end;
mmode+LR: report_illegal_case;

@ @<Glob...@>=
@!LR_ptr,@!LR_tmp:pointer; {stack of LR codes and temp for manipulation}

@ @<Declare functions needed for special kinds of nodes@>=
function new_LR(@!s:small_number): pointer;
var p: pointer; {the new node}
begin p:=get_node(small_node_size); type(p):=whatsit_node; subtype(p):=LR_node;
LR_type(p):=s; new_LR:=p;
end;

@ @<Declare functions needed for special kinds of nodes@>=
function safe_info(@!p:pointer): integer;
begin if p=null then safe_info:=-1@+else safe_info:=info(p);
end;

@ @<Append a |begin_L| to the tail of the current list@>=
tail_append(new_LR(begin_L_code))

@ @<Append an |end_L| to the tail of the current list@>=
tail_append(new_LR(end_L_code))

@ A number of routines are based on a stack of one-word nodes whose |info|
fields contain either |begin_L_code| or |begin_R_code|. The top of the
stack is pointed to by |LR_ptr|, and an auxiliary variable |LR_tmp| is
available for stack manipulation.

@d push_LR(#)==begin LR_tmp:=get_avail; info(LR_tmp):=LR_type(#);
  link(LR_tmp):=LR_ptr; LR_ptr:=LR_tmp;
  end
@d pop_LR==begin LR_tmp:=LR_ptr; LR_ptr:=link(LR_tmp); free_avail(LR_tmp);
  end

@<Flush the LR stack@>=while LR_ptr<>null do pop_LR

@ @<Insert LR nodes at the beginning of the current line@>=
while LR_ptr<>null do
  begin LR_tmp:=new_LR(info(LR_ptr)); link(LR_tmp):=link(temp_head);
  link(temp_head):=LR_tmp; pop_LR;
  end

@ @<Adjust the LR stack based on LR nodes in this line@>=
q:=link(temp_head);
while q<>cur_break(cur_p) do
  begin if notis_char_node(q) then if type(q)=whatsit_node then
   if subtype(q)=LR_node then
    if begin_LR(q) then push_LR(q)
    else if LR_ptr<>null then
     if info(LR_ptr)=begin_LR_type(q) then pop_LR;
  q:=link(q);
  end

@ We use the fact that |q| now points to the node with \.{\\rightskip} glue.

@<Insert LR nodes at the end of the current line@>=
if LR_ptr<>null then
  begin s:=temp_head; r:=link(s);
  while r<>q do
    begin s:=r; r:=link(s);
    end;
  r:=LR_ptr;
  while r<>null do
    begin LR_tmp:=new_LR(info(r)+end_L_code);
    link(s):=LR_tmp; s:=LR_tmp; r:=link(r);
    end;
  link(s):=q;
  end

@ @<Adjust the LR stack for the |hpack| routine@>=
if begin_LR(p) then push_LR(p)
else if safe_info(LR_ptr)=begin_LR_type(p) then pop_LR
else  begin incr(LR_problems);
  while link(q)<>p do q:=link(q);
  link(q):=link(p); free_node(p,small_node_size); p:=q;
  end

@ @<Check for LR anomalies at the end of |hpack|@>=
if LR_ptr<>null then
  begin while link(q)<>null do q:=link(q);
  repeat link(q):=new_LR(info(LR_ptr)+end_L_code); q:=link(q);
  LR_problems:=LR_problems+10000; pop_LR;
  until LR_ptr=null;
  end;
if LR_problems>0 then
  begin print_ln; print_nl("\endL or \endR problem (");@/
  print_int(LR_problems div 10000); print(" missing, ");@/
  print_int(LR_problems mod 10000); print(" extra");@/
  LR_problems:=0; goto common_ending;
  end

@ @<Output a reflection instruction if the direction has changed@>=
if begin_LR(p) then
  begin if safe_info(LR_ptr)<>LR_type(p) then
    begin synch_h; synch_v; dvi_out(begin_reflect);
    end;
  push_LR(p);
  end
else if safe_info(LR_ptr)=begin_LR_type(p) then
  begin pop_LR;
  if info(LR_ptr)+end_L_code<>LR_type(p) then
    begin synch_h; synch_v; dvi_out(end_reflect);
    end;
  end
else confusion("LR")
@:this can't happen LR}{\quad LR@>


@ Finally, here are the remaining things needed to make the implementation
complete at {\mc SAIL}.
@^system dependencies@>

@ The |pseudo_typein| variable is set nonzero if the |error| routine
uses the `\.E' option to exit and edit.

@<Glob...@>=
@!pseudo_typein:str_number;

@ @<Set init...@>=
pseudo_typein:=0; page:=0;

@ The |mem| array is declared after the other global variables, so
that our friendly \PASCAL\ will compile things correctly.

@<Glob...@>=
@!mem : array[mem_min..mem_max] of memory_word; {the big dynamic storage area}
@z