cwebman.tex

著名算法大师高爷爷设计的语言。此语言结合了Tex和C

The first line says that grammar rule 4 has just been applied, and \.{CWEAVE}
currently has in its memory a sequence of chunks of \TEX/ code (called
``scraps'') that are respectively
of type \\{exp} (for expression), open-parenthesis,
\\{exp} again, close-parenthesis, and further scraps that haven't yet
been considered by the parser.  (The \.+ and \.- signs stipulate that
\TEX/ should be in or out of math mode at the scrap boundaries. The \.* shows
the parser's current position.)
Then rule 11 is applied, and
the sequence $(\,exp\,)$ becomes an \\{exp} and so on.  In the
end the whole \CEE/ text has become one big scrap of type \\{function}.

Sometimes things don't work as smoothly, and you get a bunch of
lines lumped together.  This means that \.{CWEAVE} could not
digest something in your \CEE/ code.  For instance, suppose
`\.{@<Argument definitions@>}' had appeared instead of
`\.{char **argv;}' in the program above. Then \.{CWEAVE} would have
been somewhat mystified, since it thinks that section names
are just \\{exp}s.  Thus it would tell \TEX/ to format
`\X2:Argument declarations\X' on the same line as
`$\\{main}(\\{argc},\39\\{argv}{}$)'.
In this case you should help \.{CWEAVE} by putting `\.{@/}' after
`\.{main(argc,argv)}'.

\.{CWEAVE} automatically inserts a bit of extra space between declarations
and the first apparent statement of a block. One way to defeat this
spacing locally is
$$\vbox{\halign{#\hfil\cr
\.{int x;@+@t\}\\6\{@>}\cr
\.{@<Other locals@>@;@\#}\cr}}$$
the `\.{@\#}' will put extra space after `$\langle\,$Other locals$\,\rangle$'.

\section Hypertext and hyperdocumentation.

Many people have of course noticed analogies between \.{CWEB} and the
World Wide Web. The \.{CWEB} macros are in fact set up so that the output of
\.{CWEAVE} can be converted easily into Portable Document Format,
with clickable hyperlinks that can be read with Adobe's Acrobat Reader,
using a widely available open-source program called \.{dvipdfm} developed
by Mark~A. Wicks. After using \.{CWEAVE} to convert \.{cob.w} into
\.{cob.tex}, you can prepare and view a hypertext version of the program
by giving the commands
$$\vbox{\halign{\.{#}\hfil\cr
tex "\\let\\pdf+ \\input cob"\cr
dvipdfm cob\cr
acroread cob.pdf\cr}}$$
instead of invoking \TeX\ in the normal way. (Thanks to Hans Hagen,
C\'esar Augusto Rorato Crusius, and Julian Gilbey
for the macros that make this work.)
Alternatively, thanks to H\`an Th\^e\kern-.3em\raise.3ex\hbox{\'{}} Th\`anh
and Andreas Scherer, you can generate \.{cob.pdf} in one step by simply
saying `\.{pdftex}~\.{cob}'.

A more elaborate system called \.{CTWILL}, which extends the usual cross
references of \.{CWEAVE} by preparing links from the uses of identifiers
to their definitions, is also available---provided that you are willing
to work a bit harder in cases where an identifier is multiply defined.
\.{CTWILL} is intended primarily for hardcopy output, but its principles
could be used for hypertext as well.
See Chapter 11 of {\sl Digital Typography\/} by D.~E. Knuth (1999), and
the program sources at \.{ftp://ftp.cs.stanford.edu/pub/ctwill}.

\section Appendices.

As an example of a real program written in \.{CWEB}, Appendix~A
contains an excerpt from the \.{CWEB} program itself.  The reader who
examines the listings in this appendix carefully will get a good
feeling for the basic ideas of \.{CWEB}.

Appendix B is the file that sets \TEX/ up to accept
the output of \.{CWEAVE}, and Appendix~C discusses how to use some of those
macros to vary the output formats.

A ``long'' version of this manual, which can be produced from the \.{CWEB}
sources via the \UNIX/ command \.{make} \.{fullmanual}, also contains
appendices D, E, and~F, which exhibit the complete source code for
\.{CTANGLE} and \.{CWEAVE}.

\vfil\eject\titletrue

\def\runninghead{APPENDIX A --- {\tentt CWEB} FILE FORMAT}
\section Appendix A: Excerpts from a \.{CWEB} Program.

This appendix consists
of four listings.  The first shows the \.{CWEB} input that
generated sections 12--15 of the file \.{common.w}, which contains
routines common to \.{CWEAVE} and \.{CTANGLE}.
Note that some of the lines are indented to show the program structure;
the indentation is ignored by \.{CWEAVE} and \.{CTANGLE}, but users find
that \.{CWEB} files are quite readable if they have some such indentation.

The second and third listings
show corresponding parts
of the \CEE/ code output by \.{CTANGLE} and of
the corresponding \TEX/ code output by \.{CWEAVE}, when run on \.{common.w}.
The fourth listing shows how that output looks when printed out.

\vskip 6pt
\begingroup \def\tt{\eighttt} \baselineskip9pt
\verbatim
@ Procedure |prime_the_change_buffer|
sets |change_buffer| in preparation for the next matching operation.
Since blank lines in the change file are not used for matching, we have
|(change_limit==change_buffer && !!changing)| if and only if
the change file is exhausted. This procedure is called only when
|changing| is 1; hence error messages will be reported correctly.

@c
void
prime_the_change_buffer()
{
  change_limit=change_buffer; /* this value is used if the change file ends */
  @<Skip over comment lines in the change file; |return| if end of file@>;
  @<Skip to the next nonblank line; |return| if end of file@>;
  @<Move |buffer| and |limit| to |change_buffer| and |change_limit|@>;
}

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

@<Skip over comment lines in the change file...@>=
while(1) {
  change_line++;
  if (!!input_ln(change_file)) return;
  if (limit<buffer+2) continue;
  if (buffer[0]!!='@@') continue;
  if (xisupper(buffer[1])) buffer[1]=tolower(buffer[1]);
  if (buffer[1]=='x') break;
  if (buffer[1]=='y' || buffer[1]=='z' || buffer[1]=='i') {
    loc=buffer+2;
    err_print("!! Missing @@x in change file");
@.Missing @@x...@>
  }
}

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

@<Skip to the next nonblank line...@>=
do {
  change_line++;
  if (!!input_ln(change_file)) {
    err_print("!! Change file ended after @@x");
@.Change file ended...@>
    return;
  }
} while (limit==buffer);

@ @<Move |buffer| and |limit| to |change_buffer| and |change_limit|@>=
{
  change_limit=change_buffer-buffer+limit;
  strncpy(change_buffer,buffer,limit-buffer+1);
}

!endgroup
\endgroup
\vfill\eject

\def\runninghead{APPENDIX A  --- TRANSLATION BY {\tentt CTANGLE}}

Here's the portion of the \CEE/ code generated by \.{CTANGLE} that corresponds
to the source on the preceding page.  Notice that sections~13, 14 and~15
have been tangled into section~12.

\vskip6pt
\begingroup \def\tt{\eighttt} \baselineskip9pt
\verbatim
/*:9*//*12:*/
#line 247 "common.w"

void
prime_the_change_buffer()
{
change_limit= change_buffer;
/*13:*/
#line 261 "common.w"

while(1){
change_line++;
if(!!input_ln(change_file))return;
if(limit<buffer+2)continue;
if(buffer[0]!!='@')continue;
if(xisupper(buffer[1]))buffer[1]= tolower(buffer[1]);
if(buffer[1]=='x')break;
if(buffer[1]=='y'||buffer[1]=='z'||buffer[1]=='i'){
loc= buffer+2;
err_print("!! Missing @x in change file");

}
}

/*:13*/
#line 252 "common.w"
;
/*14:*/
#line 278 "common.w"

do{
change_line++;
if(!!input_ln(change_file)){
err_print("!! Change file ended after @x");

return;
}
}while(limit==buffer);

/*:14*/
#line 253 "common.w"
;
/*15:*/
#line 288 "common.w"

{
change_limit= change_buffer-buffer+limit;
strncpy(change_buffer,buffer,limit-buffer+1);
}

/*:15*/
#line 254 "common.w"
;
}

/*:12*//*16:*/
!endgroup
\endgroup
\vfill\eject

\def\runninghead{APPENDIX A --- TRANSLATION BY {\tentt CWEAVE}}

Here is the corresponding excerpt from \.{common.tex}.

\vskip6pt
\begingroup \def\tt{\eighttt} \baselineskip9pt
\verbatim
\M{12}Procedure \PB{\\{prime\_the\_change\_buffer}}
sets \PB{\\{change\_buffer}} in preparation for the next matching operation.
Since blank lines in the change file are not used for matching, we have
\PB{$(\\{change\_limit}\E\\{change\_buffer}\W\R\\{changing})$} if and only if
the change file is exhausted. This procedure is called only when
\PB{\\{changing}} is 1; hence error messages will be reported correctly.
!vskip-.5!baselineskip
\Y\B\&{void} \\{prime\_the\_change\_buffer}(\,)\1\1\2\2\6
${}\{{}$\1\6
${}\\{change\_limit}\K\\{change\_buffer}{}$;\C{ this value is used if the
change file ends }\6
\X13:Skip over comment lines in the change file; \PB{\&{return}} if end of file%
\X;\6
\X14:Skip to the next nonblank line; \PB{\&{return}} if end of file\X;\6
\X15:Move \PB{\\{buffer}} and \PB{\\{limit}} to \PB{\\{change\_buffer}} and %
\PB{\\{change\_limit}}\X;\6
\4${}\}{}$\2\par
\fi
!vskip-.5!baselineskip
\M{13}While looking for a line that begins with \.{@x} in the change file, we
allow lines that begin with \.{@}, as long as they don't begin with \.{@y},
\.{@z}, or \.{@i} (which would probably mean that the change file is fouled
up).
!vskip-.5!baselineskip
\Y\B\4\X13:Skip over comment lines in the change file; \PB{\&{return}} if end
of file\X${}\E{}$\6
\&{while} (\T{1})\5
${}\{{}$\1\6
${}\\{change\_line}\PP;{}$\6
\&{if} ${}(\R\\{input\_ln}(\\{change\_file})){}$\1\5
\&{return};\2\6
\&{if} ${}(\\{limit}<\\{buffer}+\T{2}){}$\1\5
\&{continue};\2\6
\&{if} ${}(\\{buffer}[\T{0}]\I\.{'@'}){}$\1\5
\&{continue};\2\6
\&{if} (\\{xisupper}(\\{buffer}[\T{1}]))\1\5
${}\\{buffer}[\T{1}]\K\\{tolower}(\\{buffer}[\T{1}]);{}$\2\6
\&{if} ${}(\\{buffer}[\T{1}]\E\.{'x'}){}$\1\5
\&{break};\2\6
\&{if} ${}(\\{buffer}[\T{1}]\E\.{'y'}\V\\{buffer}[\T{1}]\E\.{'z'}\V\\{buffer}[%
\T{1}]\E\.{'