begin "UNDEK"
comment Changes Knuth's WEB files into standard Ascii, by DRF.
The conversion is:
	null ('0) is removed
	down-arrow ('1) becomes underline ("←" = '137)
	and-sign ('4) becomes "and"
	not-sign ('5) becomes "not"
	element-sign ('6) becomes "in"
	tab ('11) becomes "  " (two spaces)
	line-feed ('12) stays the same
	form-feed ('14) becomes carriage-return + line-feed
	carriage-return ('15) stays the same
	circle-star ('26) becomes "&"
	underline ('30) becomes underline ("←" = '137) (SCORE only)
	not-equal ('33) becomes "<>"
	less-or-equal ('34) becomes "<="
	greater-or-equal ('35) becomes ">="
	equivalence-sign ('36) becomes "=="
	or-sign ('37) becomes "or"
	left-arrow ('137) becomes ":="

No other character less than space ('40) should be in the file, and
an error message will be produced if there is.

Note that both ↓ and _ are mapped to ascii '137, which might come out
looking like underline (preferred) or left-arrow.  The suascii ↓ should
only occur in tex-mode to indicate subscripts.  The suascii _ can also
appear in identifiers and single or double quoted strings.

This program also checks for other possible errors: If the expanded version
of any line is longer than 80 characters, the user is notified.  Also, if
any of the `special' characters above show up between dollar signs, this fact
is reported.  Actually, it is necessary to detect this latter error in a
heuristic (read: fallible) way.  It will fail if you have a dollar sign in
a quoted string along with other characters (so '$' is ok, but not " $ ").

So, to make an exportable version of everything, follow these
confusing steps:

(1) FTP TANGLE.WEB, WEAVE.WEB, TANGLE.PAS and WEBHDR.TEX in ASCII mode
	from SAIL.  Note that this puts right-curleys and tildes where they
	should be, but you must change the single-quoted 'control-x' in
	TANGLE.PAS, and the \def\'control-x' and \let\'control-x' in
	WEBHDR.TEX to '←' yourself.  You might also want to check that
	you have an up-to-date BASIC.TEX, with the same change.  WEBHDR
	and BASIC should have tabs changed to two spaces, also.
(2) Compile TANGLE.PAS, resulting in an SU-ASCII version of TANGLE.EXE.
(3) Edit TANGLE.WEB, turn off the STANFORD-DROFNATS switch, giving TANGLE.WEB'.
(4) Run UNDEK (this program) on TANGLE.WEB', producing the transportable
	version, TANGLE.WEB''.
(5) Run TANGLE.EXE on TANGLE.WEB'' to produce the transportable TANGLE.PAS''.
(6) Compile TANGLE.PAS'', resulting in a US-ASCII version of TANGLE.EXE''
(7) As a test, run TANGLE.EXE'' on TANGLE.WEB''.  The output should be
	the same as TANGLE.PAS''.
(8) Repeat steps (3) through (5) on WEAVE.WEB, giving transportable
	WEAVE.WEB'' and WEAVE.PAS''.
(9) As a test, compile WEAVE.PAS'' and run it against TANGLE.WEB'' and
	WEAVE.WEB''.  The resulting TEX files should be nearly the same
	as TANGLE.TEX and WEAVE.TEX at Sail.  If you change _ and ↓ to ←,
	⊗ to &, and tab to two spaces in a local copy of the Sail versions,
	it will be easier to do the comparisons.  The only differences you
	should notice will be due to DROFNATS being turned off, and a few
	line breaks will be different owing to tabs having been turned into
	two spaces before Weave processing.

Now you've got {TANGLE|WEAVE}.{PAS|WEB}'', all of which should be
suitable for sending to other sites.
;

require "{}{}" delimiters;
define #={; comment};
external integer !skip!;
define SAIL=true, SCORE=false # choose one to get the correct runtimes and
				character set;
define DEBUG=false;
define MAXDEPTH=100;
define crlf={13&10};

integer ifile, ofile # input and output files;
string line # input line from ifile;
integer aline # break table to read a line;
integer brchar # eoln character--test if line too long;
integer pageno, lineno # page and line number in ifile for error messages;
integer eof # true on eof of ifile;
string array tran[1:127] # character mapping - null removed on input;

IFC DEBUG THENC
define HISTMAX=10;
integer histptr; string array history[0:HISTMAX-1];
ENDC

procedure error(string s); begin integer i;
	print("UNDEK error p. ",pageno,", l. ",lineno,": ",s,crlf);
IFC DEBUG THENC
	i←(histptr+1) mod HISTMAX;
	while i≠histptr do begin
		if history[i] then print(crlf,history[i]);
		i←(i+1) mod HISTMAX;
		end;
	print(crlf);
ENDC
	end;

procedure initialize; begin integer i;
IFC SCORE THENC
	print("Input file: "); ifile←openfile("","RO");
	print("Output file: "); ofile←openfile("","W");
	setinput(ifile,99,brchar,eof);
ELSEC
	open(ifile←getchan,"DSK",0,19,0,99,brchar,eof);
	open(ofile←getchan,"DSK",0,0,19,0,0,!SKIP!);
	do begin print("Input file: "); lookup(ifile,inchwl,!SKIP!);
		if !SKIP! then print("Nope. Try again.",crlf);
	end until not !SKIP!;
	do begin print("Output file: "); enter(ofile,inchwl,!SKIP!);
		if !SKIP! then print("Nope. Try again.",crlf);
	end until not !SKIP!;
ENDC
	setbreak(aline←getbreak,'12,'15,"INS");
	pageno←1; lineno←0;
	for i←1 step 1 until 127 do tran[i]←"";
	tran['1]←"←";
	tran['4]←"and";
	tran['5]←"not";
	tran['6]←"in";
	tran['11]←"  " # tab;
	tran['12]←'12 # line-feed;
	tran['14]←'15&'12 # form-feed;
	tran['15]←'15 # carriage-return;
	tran['26]←"&" # circle-star;
	tran['30]←"←" # underline;
	tran['33]←"<>";
	tran['34]←"<=";
	tran['35]←">=";
	tran['36]←"==";
	tran['37]←"or";
	for i←'40 step 1 until '136 do tran[i]←i;
	tran['137]←":=";
	for i←'140 step 1 until '176 do tran[i]←i;
IFC SAIL THENC
	tran['32]←'32 # make the funny tilde ok at SAIL;
	tran['30]←'30 # and underline stays ok too;
	tran['175]←"" # and ALT is no good;
ENDC
IFC DEBUG THENC
	histptr←0;
ENDC
	end;

boolean inmath, inmathmath, inpascal;

# Main program;
initialize;
line←input(ifile,aline);
IFC SAIL THENC
if equ(line[1 to 9],"COMMENT ⊗") then begin integer c;
	do line←input(ifile,aline) until line='14;
	c←lop(line) # drop form-feed;
	pageno←2; lineno←0;
	end;
ENDC
inmath←inmathmath←false;
while true do begin "process a line" string res,new; integer c; string t;
	if line='14 then begin lineno←1; pageno←pageno+1; end
	else lineno←lineno+1;
	if eof=0 and brchar=0 then error("Long input line broken.");
	if eof and length(line)=0 then done "process a line" # eof of input;
	res←"";
	while line do begin integer lastc;
		lastc←c;
		res←res&(new←tran[c←lop(line)]);
		if length(new)=0 then error("Unexpected char: '"&cvos(c));
IFC DEBUG THENC
		if inmath then t←"M" else t←"";
		if inmathmath then t←t&"MM";
		history[histptr]←t;
		histptr←(histptr+1) mod HISTMAX;
ENDC
		case c of begin
		["$"] begin
			if line="$" then begin
				res←res&(c←lop(line)) # munch it up;
				inmathmath←not inmathmath;
				if (not inmathmath) and inmath then
					error("Math nesting confusion");
				if inmathmath then inpascal←false;
				end
			else if not ((line=""""=lastc) or (line="'"=lastc)) then begin
				inmath←not inmath;
				if inmath then inpascal←false;
				end;
			end;
		["|"] inpascal←not inpascal;
		else begin
			if length(new)>1 and (inmath or inmathmath) and not inpascal then
				error("Math-mode char "&new);
			end
		 end # of case stmt;
		end;
	if length(res)>80 then error("Line too long: "&cvs(length(res)));
	out(ofile,res&13&10);
	if res="" then inmath←inmathmath←false;
	if eof then done;
	line←input(ifile,aline);
	end "process a line";
release(ifile); release(ofile);
end "UNDEK";