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\input cwebmac
\parskip 0pt plus 1pt
\def\RA{\char'31 } % right arrow
\def\hang{\hangindent 4em\ignorespaces}
\font\ninerm=cmr9
\font\ninett=cmtt9
\font\eighttt=cmtt8
\def\Pascal{Pascal}
\def\cee{C}
\font\quoterm=cmssq8
\font\quoteit=cmssqi8
\def\pb{\.{|...|}}
\def\v{\.{\char'174}} % vertical (|) in typewriter font
\def\lpile{\def\cr{\hfill\endline}\matrix} % I only use \lpile by itself

\outer\def\section #1.{\penalty-50\vskip 12pt plus 3pt minus 3pt
  \noindent{\bf #1.}\quad\ignorespaces}

\def\titlepage{T}
\def\lheader{\mainfont\the\pageno\hfill\sc\runninghead\hfill}
\def\rheader{\hfill\ifnum\the\pageno=1\else\sc\runninghead\hfill
  \mainfont\the\pageno\fi}
\def\runninghead{{\tentt CWEB} USER MANUAL}
\def\narrower{\medskip\bgroup\rightskip=24pt\leftskip=24pt}
\def\endnarrower{\medskip\egroup}

% This verbatim mode assumed that no ? appears in the text being copied.
\def\verbatim{\begingroup
  \def\do##1{\catcode`##1=12 } \dospecials
  \parskip 0pt \parindent 0pt
  \catcode`\ =13 \catcode`\^^M=13
  \tt \catcode`\?=0 \verbatimdefs \verbatimgobble}
{\catcode`\^^M=13{\catcode`\ =13\gdef\verbatimdefs{\def^^M{\ \par}\let =\ }} %
  \gdef\verbatimgobble#1^^M{}}

\centerline{\titlefont A \cee\ version of {\ttitlefont WEB}}

\vskip 15pt plus 3pt minus 3pt
\section Introduction.
This document describes a version of Don Knuth's \.{WEB} system of
structured documentation, adapted to \cee\ by Silvio Levy.  This version
was entirely rewritten in \cee, and many changes were made to take
advantage of features offered by \cee\ but non-existent in \Pascal.

The bulk of this document, not counting appendixes~A--E, consists of
quotes from Knuth's memo ``The \.{WEB} System of Structured
Documentation;'' these quotes are clearly distinguished by their indentation,
and apart from the substitution of the word ``\cee'' for ``\Pascal''
and of `\.{@c}' for `\.{@p}'
all other changes to them are explicitly indicated.
This also serves to indicate which commands and features are common
to both versions of \.{WEB} and which are characteristic of this
version (of course if you're new to \.{WEB} you don't
have to worry about this).

\narrower
The philosophy behind \.{WEB} is
that an experienced system programmer, who wants to provide the best
possible documentation of his or her software products, needs two things
simultaneously:  a language like \TeX\ for formatting, and a language like
\cee\ for programming. Neither type of language can provide the
best documentation by itself; but when both are appropriately combined, we
obtain a system that is much more useful than either language separately.

The structure of a software program may be thought of as a ``web'' that is
made up of many interconnected pieces. To document such a program, we want
to explain each individual part of the web and how it relates to its
neighbors. The typographic tools provided by \TeX\ give us an opportunity
to explain the local structure of each part by making that structure
visible, and the programming tools provided by \cee\ make it possible
for us to specify the algorithms formally and unambiguously. By combining
the two, we can develop a style of programming that maximizes our ability
to perceive the structure of a complex piece of software, and at the same
time the documented programs can be mechanically translated into a working
software system that matches the documentation. \dots

Besides providing a documentation tool, \.{WEB} enhances the \cee\
language by providing \dots\ the
ability to permute pieces of the program text, so that a large system can
be understood entirely in terms of small modules and their local
interrelationships.  The \.{TANGLE} program is so named because it takes a
given web and moves the modules from their web structure into the order
required by \cee; the advantage of programming in \.{WEB} is that the
algorithms can be expressed in ``untangled'' form, with each module
explained separately.  The \.{WEAVE} program is so named because it takes
a given web and intertwines the \TeX\ and \cee\ portions contained in
each module, then it knits the whole fabric into a structured document.
(Get it? Wow.)  Perhaps there is some deep connection here with the fact
that the German word for ``weave'' is ``{\it web\/}'', and the
corresponding Latin imperative is ``{\it texe\/}''!
\endnarrower

A user of this version of \.{WEB} should be fairly familiar with the \cee\
programming language.  A minimal amount of acquaintance with \TeX\ is also
desirable, but in fact it can be acquired as one uses \.{WEB}, since
straight text can be typeset in \TeX\ with virtually no knowledge of
the language.  To someone familiar with \cee\ and \TeX\ the amount of
effort necessary to learn the commands of \.{WEB} is small.

\section The language.
As mentioned above, in writing a \.{WEB} program the user keeps the
\cee\ code and the documentation in the same file, called the \.{WEB}
file and generally named \.{something.web}.  The command
`\.{weave something}' creates an output file \.{something.tex}, which
can then be fed to \TeX, yielding a ``pretty printed'' version of
\.{something.web} that correctly handles
typographic details like page layout and the use of indentation,
italics, boldface, etc., and that includes extensive cross-index
information that is gathered automatically.  Similarly, if you run the
command \.{tangle something} you will get a \cee\ file \.{something.c},
with can then be compiled to yield executable code.

\narrower
Two kinds of material go into \.{WEB} files: \TeX\ text and \cee\ text.
A programmer writing in \.{WEB} should be thinking both of the
documentation and of the \cee\ program that he or she is creating;
i.e., the programmer should be instinctively aware of the different
actions that \.{WEAVE} and \.{TANGLE} will perform on the \.{WEB} file.
\TeX\ text is essentially copied without change by \.{WEAVE}, and it is
entirely deleted by \.{TANGLE}, since the \TeX\ text is ``pure
documentation.'' \cee\ text, on the other hand, is formatted by
\.{WEAVE} and it is shuffled around by \.{TANGLE}, according to rules that
will become clear later. For now the important point to keep in mind is
that there are two kinds of text. Writing \.{WEB} programs is something
like writing \TeX\ documents, but with an additional ``\cee\ mode''
that is added to \TeX's horizontal mode, vertical mode, and math mode.

A \.{WEB} file is built up from units called {\sl modules\/} that are more
or less self-contained.  Each module has three parts:

\yskip\item{1)} A \TeX\ part, containing explanatory material about what
is going on in the module.

\item{2)} A definition part, containing macro definitions that serve as
abbreviations for \cee\ constructions that would be less comprehensible
if written out in full each time [they are turned by \.{TANGLE} into
preprocessor macro definitions].

\item{3)} A \cee\ part, containing a piece of the program that
\.{TANGLE} will produce. This \cee\ code should ideally be about a
dozen lines long, so that it is easily comprehensible as a unit and so
that its structure is readily perceived.

\yskip\noindent The three parts of each module must appear in this order;
i.e., the \TeX\ commentary must come first, then the definitions, and
finally the \cee\ code. Any of the parts may be empty.

A module begins with [either of the two] symbols `\.{@\ }' or `\.{@*}', where
`\.{\ }' denotes a blank space. A module ends
at the beginning of the next module (i.e., at the next
`\.{@\ }' or `\.{@*}'), or at the end of the file, whichever comes first.
The \.{WEB} file may also contain material that is not part of any module
at all, namely the text (if any) that occurs before the first module.
Such text is said to be ``in limbo''; it is ignored by \.{TANGLE}
and copied essentially verbatim by \.{WEAVE}, so its function is to
provide any additional formatting instructions that may be desired in the
\TeX\ output. Indeed, it is customary to begin a \.{WEB} file with
\TeX\ code in limbo that loads special fonts, defines special macros,
changes the page sizes, and/or produces a title page.

Modules are numbered consecutively, starting with 1; these numbers appear
at the beginning of each module of the \TeX\ documentation, and they appear
as bracketed comments at the beginning of the code generated by that
module in the \cee\ program.

Fortunately, you never mention these numbers yourself when you are writing
in \.{WEB}. You just say `\.{@\ }' or `\.{@*}' at the beginning of each
new module, and the numbers are supplied automatically by \.{WEAVE} and
\.{TANGLE}. As far as you are concerned, a module has a
name instead of a number; such a name is specified by writing
`\.{@<}' followed by \TeX\ text followed by `\.{@>}'. When \.{WEAVE}
outputs a module name, it replaces the `\.{@<}' and `\.{@>}' by
angle brackets and inserts the module number in small type. Thus, when you
read the output of \.{WEAVE} it is easy to locate any module that is
referred to in another module.

For expository purposes, a module name should be a good description of the
contents of that module, i.e., it should stand for the abstraction
represented by the module; then the module can be ``plugged into'' one or
more other modules so that the unimportant details of its inner workings
are suppressed.  A module name therefore ought to be long enough to convey
the necessary meaning. Unfortunately, however, it is laborious to type
such long names over and over again, and it is also difficult to specify a
long name twice in exactly the same way so that \.{WEAVE} and \.{TANGLE}
will be able to match the names to the modules. Therefore a module name
can be abbreviated after its first appearance in the \.{WEB} file, by
typing `\.{@<$\alpha$...@>}', where $\alpha$ is any string that is a prefix of
exactly one module name that appears in the file. For example, `\.{@<Clear
the arrays@>}' can be abbreviated to `\.{@<Clear...@>}' if no other module
name begins with the five letters `\.{Clear}'. Module names must otherwise
match character for character, except that consecutive blank spaces and/or
tab marks are treated as equivalent to single spaces, and such spaces are
deleted at the beginning and end of the name. Thus, `\.{@< Clear { }the
arrays @>}' will also match the name in the previous example.

We have said that a module begins with `\.{@\ }' or `\.{@*}', but we
didn't say how it gets divided up into a \TeX\ part, a definition part,
and a \cee\ part. The definition part begins with the first appearance
of `\.{@d}' or `\.{@f}' in the module, and the \cee\ part begins with
the first appearance of `\.{@c}' or `\.{@<}'. The latter option `\.{@<}'
stands for the beginning of a module name, which is the name of the module
itself. An equals sign (\.=) must follow the `\.{@>}' at the end of this
module name; you are saying, in effect, that the module name stands for
the \cee\ text that follows, so you say `$\langle\,$module
name$\,\rangle=\null$\cee\ text'. Alternatively, if the \cee\ part
begins with `\.{@c}' instead of a module name, the current module is said
to be {\sl unnamed}. Note that module names cannot appear in the
definition part of a module, because the first `\.{@<}' in a module
signals the beginning of its \cee\ part.  Any number of module names
might appear in the \cee\ part, however, once it has started.

The general idea of \.{TANGLE} is to make a \cee\ program out of these
modules in the following way: First all [the macro definitions
indicated by `\.{@d}' are turned into \cee\ preprocessor macro definitions
and copied down.  Then] the \cee\ parts of unnamed modules are copied down
[with comments removed], in order; this constitutes the initial
approximation $T_0$ to the text of the program. (There should be at least
one unnamed module, otherwise there will be no program.) Then all module
names that appear in the initial text $T_0$ are replaced by the \cee\
parts of the corresponding modules, and this substitution process
continues until no module names remain. \dots

If the same name has been given to more than one module, the \cee\ text
for that name is obtained by putting together all of the \cee\ parts in
the corresponding modules. This feature is useful, for example, in a
module named `Global variables in the outer block', since one can then
declare global variables in whatever modules those variables are
introduced. When several modules have the same name, \.{WEAVE} assigns the
first module number as the number corresponding to that name, and it
inserts a note at the bottom of that module telling the reader to `See
also sections so-and-so'; this footnote gives the numbers of all the other
modules having the same name as the present one. The \cee\ text
corresponding to a module is usually formatted by \.{WEAVE} so that the
output has an equivalence sign in place of the equals sign in the \.{WEB}
file; i.e., the output says `$\langle\,$module
name$\,\rangle\equiv\null$\cee\ text'. However, in the case of the second
and subsequent appearances of a module with the same name, this `$\equiv$'
sign is replaced by `$\mathrel+\equiv$', as an indication that the \cee\
text that follows is being appended to the \cee\ text of another module.
\endnarrower

As \.{TANGLE} starts and leaves modules, it writes down preprocessor
\.{\#line} commands, for the benefit of the compiler.  This means that
when the compiler gives you error messages, or when you debug your program,
the messages refer to line number in the \.{WEB} file, and not in the
\cee\ file.  In most cases you can even forget about the \cee\ file altogether.

\narrower
The general idea of \.{WEAVE} is to make a \.{TEX} file from the \.{WEB}
file in the following way: The first line of the \.{TEX} file
[tells \TeX\ to input a file with] macros that
define \.{WEB}'s documentation conventions. The next lines of the file
will be copied from whatever \TeX\ text is in limbo before the first
module.  Then comes the output for each module in turn, possibly
interspersed with end-of-page marks.  Finally, \.{WEAVE} will generate a
cross-reference index that lists each module number in which each \cee\
identifier appears, and it will also generate an alphabetized list
of the module names, as well as a table of contents that
shows the page and module numbers for each ``starred'' module.

What is a ``starred'' module, you ask? A module that begins with `\.{@*}'
instead of `\.{@\ }' is slightly special in that it denotes a new major
group of modules. The `\.{@*}' should be followed by the title of this
group, followed by a period. Such modules will always start on a new page
in the \TeX\ output, and the group title will appear as a running headline
on all subsequent pages until the next starred module. The title will also
appear in the table of contents, and in boldface type at the beginning of
its module. Caution:  Do not use \TeX\ control sequences in such titles,
unless you know that the \.{webmac} macros will do the right thing with
them. The reason is that these titles are converted to uppercase when
they appear as running heads, and they are converted to boldface when they
appear at the beginning of their modules, and they are also written out to
a table-of-contents file used for temporary storage while \TeX\ is
working; whatever control sequences you use must be meaningful in all
three of these modes.

The \TeX\ output produced by \.{WEAVE} for each module consists of
the following: First comes the module number (e.g., `\.{\\M123.}'
at the beginning of module 123, except that `\.{\\N}' appears in place of
`\.{\\M}' at the beginning of a starred module). Then comes the
\TeX\ part of the module, copied almost verbatim except as noted
below. Then comes the definition part and the \cee\ part, formatted
so that there will be a little extra space between them if both are
nonempty. The definition and \cee\ parts are obtained by inserting
a bunch of funny looking \TeX\ macros into the \cee\ program; these
macros handle typographic details about fonts and proper math spacing,
as well as line breaks and indentation.

When you are typing \TeX\ text, you will probably want to make frequent
reference to variables and other quantities in your \cee\ code, and you
will want those variables to have the same typographic treatment
when they appear in your text as when they appear in your
program.  Therefore the \.{WEB} language allows you to get the effect of
\cee\ editing within \TeX\ text, if you place `\.|' marks before and
after the \cee\ material. For example, suppose you want to say something
like this:
$$\hbox{If \\{pa} is declared as \&{int} ${*}\\{pa}$, the assignment
$\\{pa}={\amp}\|a[\O{0}]$ sets \\{pa} to point to the zeroth element of \|a.}$$
The \TeX\ text would look like this in your \.{WEB} file:
$$\lpile{\.{If |pa| is declared as |int *pa|, the}\cr
\.{assignment |pa=\&a[0]| sets |pa| to point
to the zeroth element of |a|.}\cr}$$
And \.{WEAVE} translates this into something you are glad you didn't have
to type:
$$\lpile{\.{If \\\\\{pa\} is declared as \\\&\{int\} \$\{*\}\\\\\{pa\}\$,
the}\cr
  \.{assignment \$\\\\\{pa\}=\{\\amp\}\\|a[\\O\{0\}]\$
  sets \\\\\{pa\} to point to the zeroth element of \\|a.}\cr}$$
Incidentally, the cross-reference index that \.{WEAVE} would make, in
the presence of a comment like this, would include
the current module number as one of the index entries for \\{pa},
even though \\{pa} might not appear in the \cee\ part of
this module. Thus, the index covers references to identifiers in
the explanatory comments as well as in the program itself; you will
soon learn to appreciate this feature. However, the identifiers
\&{int} and \|a\ would not be indexed,
because \.{WEAVE} does not make index entries for reserved words or
single-letter identifiers. Such identifiers are felt to be so ubiquitous
that it would be pointless to mention every place where they occur. \dots

Although a module begins with \TeX\ text and ends with \cee\ text, we
have noted that the dividing line isn't sharp, since \cee\ text can be
included in \TeX\ text if it is enclosed in `\pb'.  Conversely, \TeX\ text
also appears frequently within \cee\ text, because everything in
comments (i.e., between \.{/*} and right \.{*/}) is treated as \TeX\ text.
Furthermore, a module name consists of \TeX\ text; thus, a \.{WEB} file
typically involves constructions like `\.{if} \.{(x==0)}
\.{@<Empty} \.{the} \.{|buffer|} \.{array@>}' where we go back and forth
between \cee\ and \TeX\ conventions in a natural way.
\endnarrower

\section Macros.
A \.{@d} followed by
$$`\\{identifier}\.{ }\hbox{\cee\ text'}\qquad\hbox{or}\qquad
\\{identifier}\.(\\{par1},\dots,\\{parn}\.)\.{ }\hbox{\cee\ text'},$$
where there is no blank between the
\\{identifier} and the parentheses in the second case, is
transformed by \.{TANGLE} into a preprocessor command, starting with
\.{\#define}, which is printed at the top of the file.  If
for any reason you need a \.{\#define} command at a specific spot in
your \cee\ file, you can treat it as \cee\ code, instead of as a
\.{WEB} macro.

A `\.{@d}' macro definition can go on for several lines, and the
newlines don't have to be protected by backslashes, since \.{TANGLE}
itself inserts the backslashes.

\section Strings and constants.
If you want a string, delimited by pairs of \.' or \.", to appear in
the \cee\ file, you can type it exactly so in the \.{WEB} file, except
that the character `\.@' should be typed `\.{@@}' (it becomes a
control code, the only one that can appear in strings; see below).
Newlines should be protected by backslashes.

In particular, the string `\.{'A'}' in the \.{WEB} file will be copied by
\.{TANGLE} into the \cee\ file, and will be interpreted by the \cee\
compiler as the machine's code for `\.A'.  \.{WEB} offers a
way to uniformize the value of character constants, so that readily
portable programs can be easily written (\.{WEB} itself uses this
facility): if you write `\.{@'A'}' in the \.{WEB} file, \.{TANGLE} will
translate this into the ASCII code for `\.A', so the value of this
constant does not depend on the character set.  This works for all the
visible characters of the ASCII character set codes $40_8$ to $176_8$
(i.e., octal), as well as the standard \cee\ escape sequences
\.{\\n}, \.{\\t}, \.{\\b}, \.{\\r} and \.{\\f}.

Speaking of octal constants, \TeX\ and \cee\ have (unfortunately)
incompatible ways to refer to octal and hex constants.  In \TeX\ you
make a constant octal or hexadecimal by prepending \.' or \.",
respectively, to it; in \cee\ the constant should be preceded by \.0
or \.{0x}.  In \.{WEB} it seems reasonable to let each convention hold
in its respective realm; so in \cee\ text you get $40_8$ by typing
`\.{040}', which \.{TANGLE} faithfully copies into the \cee\ file (for
the compiler's benefit) and which \.{WEAVE} prints as $\O{\~40}$
(for the benefit of \TeX\ users).  For consistency, then, you
should type `\.{|040|}' in the \TeX\ part of the module.  (I'm not entirely
sure that this is what \.{WEB} should do; suggestions are welcome.)

\section Control codes.
A \.{WEB} {\sl control code\/}
is a two-character combination of which the first is `\.@'.
We've already seen the meaning of several control codes; here is a
complete list of all of them.

\narrower
The letters $L$, $T$,
$C$, $M$, $\\{Co}$, and/or $S$ following each code indicate whether or not that
code is allowable in limbo, in \TeX\ text, in \cee\ text, in module
names, in comments, and/or in strings.  A bar over such a letter means
that the control code terminates the present part of the \.{WEB} file; for
example, $\overline L$ means that this control code ends the limbo material
before the first module.

\gdef\@#1[#2] {\yskip\hangindent 2em\noindent\.{@#1\unskip
  \spacefactor1000{ }}$[#2]$\quad}
\def\oP{\overline C}
\def\oT{\overline T}

\@@ [\\{Co},L,M,C,S,T] A double \.@ denotes the single character `\.@'. This is
the only control code that is legal in limbo, in comments, and in strings.

\@\ [\overline L,\oP,\oT] This denotes the beginning of a new
(unstarred) module. A tab mark or end-of-line (carriage return)
is equivalent to a space when it follows an \.@ sign.

\@* [\overline L,\oP,\oT] This denotes the beginning of a new starred
module, i.e., a module that begins a new major group. The title of the new
group should appear after the \.{@*}, followed by a period. As explained
above, \TeX\ control sequences should be avoided in such titles unless
they are quite simple. When \.{WEAVE} and \.{TANGLE} read a \.{@*}, they
print an asterisk followed by the current module number, so that the user
can see some indication of progress. The very first module should be starred.

\@d [\oP,\oT] Macro definitions begin with \.{@d} (or \.{@D}), followed by
[an identifier and \cee\ text as explained earlier].

\@f [\oP,\oT] Format definitions begin with \.{@f} (or \.{@F}); they cause
\.{WEAVE} to treat identifiers in a special way when they appear in
\cee\ text. [The general form of a format definition is `\.{@f} \|l
\|r', followed by an optional comment enclosed between
\.{/*} and \.{*/}, where \|l and \|r
are identifiers;] \.{WEAVE} will subsequently treat identifier \|l as it
currently treats \|r. This feature allows a \.{WEB} programmer to invent
new reserved words and/or to unreserve some of \cee's reserved
identifiers. [However, the need to do this
should arise very seldom, since \.{WEAVE} knows that identifiers being
defined with a \&{typedef} should become reserved words.]
The definition part of each module consists of any number of
macro definitions (beginning with \.{@d}) and format definitions (beginning
with \.{@f}), intermixed in any order.

\@c [\oP,\oT] The \cee\ part of an unnamed module begins with \.{@c}
(or \.{@C}). This causes \.{TANGLE} to append the following \cee\ code
to the initial program text $T_0$ as explained above. The \.{WEAVE}
processor does not cause a `\.{@c}' to appear explicitly in the \TeX\
output, so if you are creating a \.{WEB} file based on a \TeX-printed
\.{WEB} documentation you have to remember to insert \.{@c} in the
appropriate places of the unnamed modules.

Because of the rules by which every module is broken into three parts,
the control codes `\.{@d}', `\.{@f}', and `\.{@c}' are not allowed to occur
once the \cee\ part of a module has begun.

\@< [C,\oT] A module name begins with \.{@<} followed by \TeX\ text followed
by \.{@>}; the \TeX\ text should not contain any \.{WEB} control sequences
except \.{@@}, unless these control sequences appear in \cee\ text that
is delimited by \pb. The module name may be abbreviated, after its first
appearance in a \.{WEB} file, by giving any unique prefix followed by \.{...},
where the three dots immediately precede the closing \.{@>}. Module names may
not appear in \cee\ text that is enclosed in \pb, nor may they appear
in the definition part of a module (since the appearance of a module name
ends the definition part and begins the \cee\ part). \dots

\@\& [C] The \.{@\&} operation causes whatever is on its left to be
adjacent to whatever is on its right, in the \cee\ output. No spaces or
line breaks will separate these two items. \dots

\@\^ [C,T] The ``control text'' that follows, up to the next
`\.{@>}', will be entered into the index together with the identifiers of
the \cee\ program; this text will appear in roman type. For example, to
put the phrase ``system dependencies'' into the index, type
`\.{@\^system dependencies@>}' in each module
that you want to index as system dependent. A control text \dots\
must end on the same line of the \.{WEB} file as it began.  Furthermore,
no \.{WEB} control sequences are allowed in a control text, not even
\.{@@}. (If you need an \.{@} sign you can get around this restriction by
typing `\.{\\AT!}'.)

\@. [C,T] The ``control text'' that follows will be entered into the index
in \.{typewriter} \.{type}; see the rules for `\.{@\^}', which is analogous.

\@: [C,T] The ``control text'' that follows will be entered into the index
in a format controlled by the \TeX\ macro `\.{\\9}', which the user
should define as desired; see the rules for `\.{@\^}', which is analogous.

\@t [C] The ``control text'' that follows, up to the next `\.{@>}', will
be put into a \TeX\ \.{\\hbox} and formatted along with the neighboring
\cee\ program. This text is ignored by \.{TANGLE}, but it can be used
for various purposes within \.{WEAVE}. For example, you can make comments
that mix \cee\ and classical mathematics, as in `$\\{size}<2^{15}$', by
typing `\.{|size < @t\$2\^\{15\}\$@>|}'.  A control text must end on the
same line of the \.{WEB} file as it began, and it may not contain any
\.{WEB} control codes.

\@= [C] The ``control text'' that follows, up to the next `\.{@>}', will
be passed verbatim to the \cee\ program.

\@! [C,T] The module number in an index entry will be underlined if `\.{@!}'
immediately precedes the identifier or control text being indexed. This
convention is used to distinguish the modules where an identifier is
defined, or where it is explained in some special way, from the modules
where it is used. A~reserved word or an identifier of length one will not
be indexed except for underlined entries. An `\.{@!}' is implicitly inserted
by \.{WEAVE} [when an identified is being defined or declared in \cee\
code; for example, the definition 
\&{int} \\{array}[\\{max\_dim}], \\{count}${}=\\{old\_count};$
makes the names \\{array} and \\{count} get an underlined entry in the
index.  Statement tags, function definitions like
$\\{main}(\\{argc},\39\\{argv})$ and \&{typedef} definitions also
imply underlining.]
\endnarrower

\@' [C] This control code replaces the next character or escape sequence
by its ASCII value.

\narrower
\@, [C] This control code inserts a thin space in \.{WEAVE}'s output; it is
ignored by \.{TANGLE}. Sometimes you need this extra space if you are using
macros in an unusual way, e.g., if two identifiers are adjacent.

\@/ [C] This control code causes a line break to occur within a \cee\
program formatted by \.{WEAVE}; it is ignored by \.{TANGLE}. Line breaks
are chosen automatically by \TeX\ according to a scheme that works 99\%\
of the time, but sometimes you will prefer to force a line break so that
the program is segmented according to logical rather than visual
criteria. \dots

\@| [C] This control code specifies an optional line break in the midst of
an expression. For example, if you have \dots\
a long expression on the right-hand side of an assignment
statement, you can use `\.{@|}' to specify breakpoints more logical than
the ones that \TeX\ might choose on visual grounds.

\@\# [C] This control code forces a line break, like \.{@/} does,
and it also causes a little extra white space to appear between the lines at
this break. You might use it, for example, \dots\
between groups of macro definitions that are logically separate but within
the same module. [\.{WEB} automatically inserts this extra space
between functions, between external declarations and functions, and
between declarations and statements within a function.]

\@+ [C] This control code cancels a line break that might otherwise be
inserted by \.{WEAVE}, e.g., before the word `\&{else}', if you want to
put a short [if--else] construction on a single line. It is ignored by
\.{TANGLE}.

\@; [C] This control code is treated like a semicolon, for formatting
purposes, except that it is invisible. You can use it, for example, after
a module name when the \cee\ text represented by that module name ends
with a semicolon.

\yskip\noindent
The last six control codes (namely `\.{@,}', `\.{@/}', `\.{@|}',
`\.{@\#}', `\.{@+}', and `\.{@;}') have no effect on the \cee\
program output by \.{TANGLE}; they merely help to improve the readability
of the \TeX-formatted \cee\ that is output by \.{WEAVE}, in unusual
circumstances. \.{WEAVE}'s built-in formatting method is fairly good
[when dealing with syntactically correct \cee\ text], but
it is incapable of handling all possible cases, because it must deal with
fragments of text involving macros and module names; these fragments do
not necessarily obey \cee's syntax. Although \.{WEB} allows you to
override the automatic formatting, your best strategy is not to worry
about such things until you have seen what \.{WEAVE} produces automatically,
since you will probably need to make only a few corrections when you are
touching up your documentation.

\endnarrower
Actually you may not like the way \.{WEAVE} handles certain
situations, for examples, the fact that statements aren't always
separated by newlines.  In that case you can customize \.{WEAVE}
by changing its grammar.  In future releases you will be able
to do so at run time, but for now you have to change the source
code.  This is not hard; you can find a list of grammar rules
in the \.{WEAVE} source listing or in the file \.{prod.web}.

You can also compile \.{WEAVE} with the \.{-DDEBUG} option on the command
line, and see how \.{WEAVE} is parsing your C code by preceding
it with the line `\.{@ @c @2}' (the control sequence `\.{@2}'
turns on the ``peeping'' mode, and `\.{@0}' turns it off).
For example, if you run \.{WEAVE} on the file
\medskip
\begingroup
\verbatim
@ @c @2
main (argc,argv)
char **argv;
{
      for (;argc>0;argc++)
	      printf("%s\n",argv[argc]);
}
?endgroup
\endgroup
\medskip\noindent
you get the following gibberish on your screen:
\medskip
\begingroup
\verbatim
[...]
4:*exp ( +exp+ )...
27:*exp +exp+ int...
5:*+exp+ int +unorbinop+...
[...]
31:*+fn_decl+ +stmt- -ignore_scrap-
20:*+function- -ignore_scrap-
56:*+function-
[...]
?endgroup
\endgroup
\medskip
The first line says that rule 4 has just been applied, and \.{WEAVE}
currently has in its memory a sequence of chunks of C code (called
``scraps'') that are of type \\{exp} (for expression), open-parenthesis,
\\{exp} again, close-parenthesis.  Then rule 27 is applied, and
the sequence $(\,exp\,)$ becomes an \\{exp} and so on.  In the
end the whole C 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 \.{WEAVE} could not
digest something in your C code.  For instance, if you had
written \.{@<Argument definitions@>} instead of
\.{char **argv;} in the program above \.{WEAVE} would have
been completely mystified, since it thinks that module names
are just \\{exp}s.  In this case you would have to help
\.{WEAVE} by writing

\begingroup
\verbatim
main (argc,argv)@/
@<Argument definitions@>@;@/
{
...
?endgroup
\endgroup

\narrower

\@{x @y @z}[\\{change\_file}]
\.{WEAVE} and \.{TANGLE} are designed to work with two input files,
called \\{web\_file} and \\{change\_file}, where \\{change\_file} contains
data that overrides selected portions of \\{web\_file}. The resulting merged
text is actually what has been called the \.{WEB} file elsewhere in this
report.

\hangindent 2em\hskip 2em
Here's how it works: The change file consists of zero or more ``changes,''
where a change has the form `\.{@x}$\langle$old lines$\rangle$\.{@y}$\langle$%
new lines$\rangle$\.{@z}'. The special control codes \.{@x}, \.{@y}, \.{@z},
which are allowed only in change files, must appear at the beginning of a line;
the remainder of such a line is ignored.
The $\langle$old lines$\rangle$ represent material that exactly matches
consecutive lines of the \\{web\_file}; the $\langle$new lines$\rangle$
represent zero or more lines that are supposed to replace the old. Whenever
the first ``old line'' of a change is found to match a line in the
\\{web\_file}, all the other lines in that change must match too.

\hangindent 2em\hskip 2em
Between changes, before the first change, and after the last change,
the change file can have any number of lines that do not begin with
`\.{@x}', `\.{@y}', or~`\.{@z}'. Such lines are bypassed and not used for
matching purposes.

\hangindent 2em\hskip 2em
This dual-input feature is useful when working with a master \.{WEB} file
that has been received from elsewhere (e.g., \.{TANGLE.WEB} or
\.{WEAVE.WEB} or \.{TEX.WEB}), when changes are desirable to customize the
program for your local computer system. You will be able to debug your
system-dependent changes without clobbering the master web file; and once
your changes are working, you will be able to incorporate them readily
into new releases of the master web file that you might receive from time
to time.
\endnarrower

\@i [\\{web\_file}] Furthermore the \\{web\_file} itself can be a combination of
several files.  When \.{WEAVE} or \.{TANGLE} are reading a file and
encounter the control code \.{@i} at the beginning of a line, they
interrupt their reading and start reading the file named after the
\.{@i}, much as the \cee\ preprocessor does when it encounters an \.{\#include}
line.  After the included file is done, they go back to the next line
of the original file.  The file name following \.{@i} can be
surrounded by \." or not; it should be made up of visible ASCII
characters only, not including \.".  Include files can nest.

\narrower
\section Additional features and caveats.

1. \dots\ In certain installations of \.{WEB} that
{\def\\#1#2{`{\tentex\char'#1#2}'}%
have an extended character set, the characters
[\\13, \\01, \\31, \\32, \\34, \\35,
\\36, \\37, and \\04}
can be used as abbreviations for `\.{++}', `\.{--}', `\.{->}',
`\.{!=}', `\.{<=}', `\.{>=}', `\.{==}', `\.{\v\v}', `\.{\&\&}',
respectively.] However, the latter abbreviations
are not used in the standard versions of \.{WEAVE.WEB} and \.{TANGLE.WEB}
that are distributed to people who are installing \.{WEB} on other
computers, and the programs are designed to produce only standard ASCII
characters as output if the input consists entirely of ASCII characters.

2. If you have an extended character set, all of the characters listed
in Appendix C of {\sl The \TeX book\/} can be used in strings. But you should
stick to standard ASCII characters if you want to write programs that will
be useful to all the poor souls out there who don't have extended
character sets.

3. The \TeX\ file output by \.{WEAVE} is broken into lines having at most
80 characters each. The algorithm that does this line breaking is unaware
of \TeX's convention about comments following `\.\%' signs on a line. When
\TeX\ text is being copied, the existing line breaks are copied as well,
so there is no problem with `\.\%' signs unless the original \.{WEB} file
contains a line more than eighty characters long or a line with \cee\
text in \pb\ that expands to more than eighty characters long. Such lines
should not have `\.\%' signs.

4. \cee\ text is translated by a ``bottom up'' procedure that
identifies each token as a ``part of speech'' and combines parts of speech
into larger and larger phrases as much as possible according to a special
grammar that is explained in the documentation of \.{WEAVE}. It is easy to
learn the translation scheme for simple constructions like single
identifiers and short expressions, just by looking at a few examples of
what \.{WEAVE} does, but the general mechanism is somewhat complex because
it must handle much more than \cee\ itself. Furthermore the output
contains embedded codes that cause \TeX\ to indent and break lines as
necessary, depending on the fonts used and the desired page width. For
best results it is wise [not to] enclose long \cee\ texts in \pb, since the
indentation and line breaking codes are omitted when the \pb\ text is
translated from \cee\ to \TeX. Stick to simple expressions or
statements.  [If a C preprocessor command is enclosed in \pb,
the \.\# that introduces it must be at the beginning of a line,
or \.{WEAVE} won't print it correctly.]

5. Comments and module names are not permitted in \pb\ text. After a `\.|'
signals the change from \TeX\ text to \cee\ text, the next `\.|' that is
not part of a string or control text ends the \cee\ text.

6. A comment must have properly nested occurrences of left and right
braces, otherwise \.{WEAVE} [will try to balance the braces to keep
\TeX\ from fouling up too much].

8. The \.{@f} feature allows you to define one identifier to act like
another, and these format definitions are carried out sequentially
\dots\ However, a given identifier has only one printed format
throughout the entire document (and this format will even be used before
the \.{@f} that defines it). The reason is that \.{WEAVE} operates in two
passes; it processes \.{@f}'s and cross-references on the first pass and
does the output on the second.

10. Sometimes it is desirable to insert spacing into \cee\ code that is
more general than the thin space provided by `\.{@,}'. The \.{@t} feature
can be used for this purpose; e.g., `\.{@t\\hskip 1in@>}' will
leave one inch of blank space. Furthermore, `\.{@t\\4@>}' can be
used to backspace by one unit of indentation, since the control sequence
\.{\\4} is defined in \.{webmac} to be such a backspace. (This
control sequence is used, for example, at the beginning of lines that
contain labeled statements, so that the label will stick out a little at
the left.)
\endnarrower

\section Appendices.
The basic ideas of \.{WEB} can be understood most easily by looking at
examples of ``real'' programs. Appendix~A shows the \.{WEB} input that
generated modules 19--20 of the \.{COMMON} file, which contains
routines common to \.{WEAVE} and \.{TANGLE}. Appendix~B shows the
corresponding \TeX\ code output by \.{WEAVE},
and Appendix~C shows how the output of \.{WEAVE} looks when printed out.
Appendix~D shows the corresponding \cee\ code output by \.{TANGLE}, 
Appendix E is the file that sets \TeX\ up to accept
the output of \.{WEAVE}, Appendix~F discusses how to use some of its macros
to vary the output formats.

The reader should first compare Appendix~A to Appendix~D; then the
same material should be compared to Appendices~B and~C.

\vfil\eject

\def\runninghead{APPENDIX A --- {\tentt WEB} FILE FORMAT}
\section Appendix A.
The following is an excerpt of the file \.{COMMON.WEB},
which contains routines shared by \.{WEAVE} and \.{TANGLE}.
Note that some of the lines are indented to show the program structure.
The indentation is ignored by \.{WEAVE} and \.{TANGLE}, but users find
that \.{WEB} files are quite readable if they have some such indentation.

\vskip 6pt
\begingroup \def\tt{\eighttt} \baselineskip9pt
\verbatim
@ The following procedure is used to see if the next change entry should
go into effect; it is called only when |changing| is 0.
The idea is to test whether or not the current
contents of |buffer| matches the current contents of |change_buffer|.
If not, there's nothing more to do; but if so, a change is called for:
All of the text down to the \.{@@y} is supposed to match. An error
message is issued if any discrepancy is found. Then the procedure
prepares to read the next line from |change_file|.

@<Func...@>=
check_change() /* switches to |change_file| if the buffers match */
{
  int n=0; /* the number of discrepancies found */
  if (lines_dont_match) return;
  while (1) {
    changing=1; print_where=1; change_line++;
    if (!input_ln(change_file)) {
      err_print("! Change file ended before @@y");
@.Change file ended...@>
      change_limit=0; changing=0; print_where=1;
      return;
    }
    @<Check for erron...@>;
    @<If the current line starts with \.{@@y},
      report any discrepancies and |return|@>;@/
    @<Move |buffer| and |limit|...@>;@/
    changing=0; print_where=1; cur_line++;
    while (!input_ln(cur_file)) { /* pop the stack or quit */
      if (include_depth==0) {
        err_print("! WEB file ended during a change");
@.WEB file ended...@>
        input_has_ended=1; return;
      }
      include_depth--; print_where=1; cur_line++;
    }
    if (lines_dont_match) n++;
  }
}

@ @<If the current line starts with \.{@@y}...@>=
if (limit>buffer+1 && buffer[0]==@'@@') {
  @<Lowerc...@>;
  if (buffer[1]==@'x' || buffer[1]==@'z') {
    loc=buffer+2; err_print("! Where is the matching @@y?");
@.Where is the match...@>
    }
  else if (buffer[1]==@'y') {
    if (n>0) {
      loc=buffer+2;
      err_print("! Hmm... some of the preceding lines failed to match");
@.Hmm... some of the preceding...@>
    }
    return;
  }
}
?endgroup
\endgroup
\vfill\eject

\def\runninghead{APPENDIX B --- TRANSLATION BY {\tentt WEAVE}}
\section Appendix B.
This excerpt from \.{COMMON.TEX} corresponds to Appendix A.

\vskip6pt
\begingroup \def\tt{\eighttt} \baselineskip9pt
\verbatim
\M19. The following procedure is used to see if the next change entry should
go into effect; it is called only when \\{changing} is 0.
The idea is to test whether or not the current
contents of \\{buffer} matches the current contents of \\{change\_buffer}.
If not, there's nothing more to do; but if so, a change is called for:
All of the text down to the \.{@y} is supposed to match. An error
message is issued if any discrepancy is found. Then the procedure
prepares to read the next line from \\{change\_file}.

\Y\P\4\X6:Functions\X${}+\S{}$\6
$\\{check\_change}(\,)$\5
\C{ switches to \\{change\_file} if the buffers match }\6
$\{$\1\6
\&{int} \|n$=\O{0};$\5
\C{ the number of discrepancies found }\7
\&{if} (\\{lines\_dont\_match})\1\5
\&{return};\2\6
\&{while} $(\O{1})$\5
$\{$\1\6
$\\{changing}=\O{1};$\5
$\\{print\_where}=\O{1};$\5
$\\{change\_line}\PP;$\6
\&{if} $(\R\\{input\_ln}(\\{change\_file}))$\5
$\{$\1\6
$\\{err\_print}(\.{"!\ Change\ file\ ended\ before\ @y"});$\5
$\\{change\_limit}=\O{0};$\5
$\\{changing}=\O{0};$\5
$\\{print\_where}=\O{1};$\5
\&{return};\6
\4$\}$\2\6
\X16:Check for erroneous \.{@i}\X;\5
\X20:If the current line starts with \.{@y}, report any discrepancies and %
\&{return}\X;\6
\X18:Move \\{buffer} and \\{limit} to \\{change\_buffer} and \\{change\_limit}%
\X;\6
$\\{changing}=\O{0};$\5
$\\{print\_where}=\O{1};$\5
$\\{cur\_line}\PP;$\6
\&{while} $(\R\\{input\_ln}(\\{cur\_file}))$\5
$\{$\5
\C{ pop the stack or quit }\1\6
\&{if} $(\\{include\_depth}\S\O{0})$\5
$\{$\1\6
$\\{err\_print}(\.{"!\ WEB\ file\ ended\ during\ a\ change"});$\5
$\\{input\_has\_ended}=\O{1};$\5
\&{return};\6
\4$\}$\2\6
$\\{include\_depth}\MM;$\5
$\\{print\_where}=\O{1};$\5
$\\{cur\_line}\PP;$\6
\4$\}$\2\6
\&{if} (\\{lines\_dont\_match})\1\5
$\|n\PP;$\2\6
\4$\}$\2\6
\4$\}$\2\par
\fi

\M20. \P\X20:If the current line starts with \.{@y}, report any discrepancies
and \&{return}\X${}\S{}$\6
\&{if} $(\\{limit}>\\{buffer}+\O{1}\W\\{buffer}[\O{0}]\S\.{@'@'})$\5
$\{$\1\6
\X15:Lowercasify $\\{buffer}[\O{1}]$\X;\6
\&{if} $(\\{buffer}[\O{1}]\S\.{@'x'}\V\\{buffer}[\O{1}]\S\.{@'z'})$\5
$\{$\1\6
$\\{loc}=\\{buffer}+\O{2};$\5
$\\{err\_print}(\.{"!\ Where\ is\ the\ matching\ @y?"});$\6
\4$\}$\2\5
\&{else} \1\&{if} $(\\{buffer}[\O{1}]\S\.{@'y'})$\5
$\{$\1\6
\&{if} $(\|n>\O{0})$\5
$\{$\1\6
$\\{loc}=\\{buffer}+\O{2};$\5
$\\{err\_print}(\.{"!\ Hmm...\ some\ of\ the\ preceding\ lines\ failed\ to\
match"});$\6
\4$\}$\2\6
\&{return};\6
\4$\}$\2\2\6
\4$\}$\2\par
\U section~19.\fi
?endgroup
\endgroup
\vfil\eject

\def\runninghead{APPENDIX C --- FINAL DOCUMENT}
\section Appendix C.
Here's what Appendix~B looks like when typeset.

\M19. The following procedure is used to see if the next change entry should
go into effect; it is called only when \\{changing} is 0.
The idea is to test whether or not the current
contents of \\{buffer} matches the current contents of \\{change\_buffer}.
If not, there's nothing more to do; but if so, a change is called for:
All of the text down to the \.{@y} is supposed to match. An error
message is issued if any discrepancy is found. Then the procedure
prepares to read the next line from \\{change\_file}.

\Y\P\4\X6:Functions\X${}+\S{}$\6
$\\{check\_change}(\,)$\5
\C{ switches to \\{change\_file} if the buffers match }\6
$\{$\1\6
\&{int} \|n$=\O{0};$\5
\C{ the number of discrepancies found }\7
\&{if} (\\{lines\_dont\_match})\1\5
\&{return};\2\6
\&{while} $(\O{1})$\5
$\{$\1\6
$\\{changing}=\O{1};$\5
$\\{print\_where}=\O{1};$\5
$\\{change\_line}\PP;$\6
\&{if} $(\R\\{input\_ln}(\\{change\_file}))$\5
$\{$\1\6
$\\{err\_print}(\.{"!\ Change\ file\ ended\ before\ @y"});$\5
$\\{change\_limit}=\O{0};$\5
$\\{changing}=\O{0};$\5
$\\{print\_where}=\O{1};$\5
\&{return};\6
\4$\}$\2\6
\X16:Check for erroneous \.{@i}\X;\5
\X20:If the current line starts with \.{@y}, report any discrepancies and %
\&{return}\X;\6
\X18:Move \\{buffer} and \\{limit} to \\{change\_buffer} and \\{change\_limit}%
\X;\6
$\\{changing}=\O{0};$\5
$\\{print\_where}=\O{1};$\5
$\\{cur\_line}\PP;$\6
\&{while} $(\R\\{input\_ln}(\\{cur\_file}))$\5
$\{$\5
\C{ pop the stack or quit }\1\6
\&{if} $(\\{include\_depth}\S\O{0})$\5
$\{$\1\6
$\\{err\_print}(\.{"!\ WEB\ file\ ended\ during\ a\ change"});$\5
$\\{input\_has\_ended}=\O{1};$\5
\&{return};\6
\4$\}$\2\6
$\\{include\_depth}\MM;$\5
$\\{print\_where}=\O{1};$\5
$\\{cur\_line}\PP;$\6
\4$\}$\2\6
\&{if} (\\{lines\_dont\_match})\1\5
$\|n\PP;$\2\6
\4$\}$\2\6
\4$\}$\2\par
\fi

\M20. \P\X20:If the current line starts with \.{@y}, report any discrepancies
and \&{return}\X${}\S{}$\6
\&{if} $(\\{limit}>\\{buffer}+\O{1}\W\\{buffer}[\O{0}]\S\.{@'@'})$\5
$\{$\1\6
\X15:Lowercasify $\\{buffer}[\O{1}]$\X;\6
\&{if} $(\\{buffer}[\O{1}]\S\.{@'x'}\V\\{buffer}[\O{1}]\S\.{@'z'})$\5
$\{$\1\6
$\\{loc}=\\{buffer}+\O{2};$\5
$\\{err\_print}(\.{"!\ Where\ is\ the\ matching\ @y?"});$\6
\4$\}$\2\5
\&{else} \1\&{if} $(\\{buffer}[\O{1}]\S\.{@'y'})$\5
$\{$\1\6
\&{if} $(\|n>\O{0})$\5
$\{$\1\6
$\\{loc}=\\{buffer}+\O{2};$\5
$\\{err\_print}(\.{"!\ Hmm...\ some\ of\ the\ preceding\ lines\ failed\ to\
match"});$\6
\4$\}$\2\6
\&{return};\6
\4$\}$\2\2\6
\4$\}$\2\par
\U section~19.\fi
\vfil\eject

\def\runninghead{APPENDIX D --- TRANSLATION BY {\tentt TANGLE}}
\section Appendix D.
Here's the portion of the \cee\ code generated by \.{TANGLE} that corresponds
to Appendix~A.  Notice that module~15 has been tangled into module~20,
and modules~16, 18 and~20 have been tangled into module~19.

\vskip6pt
\begingroup \def\tt{\eighttt} \baselineskip9pt
\verbatim
/*:13*//*19:*/
#line 372 "common.web"

check_change()
{
int n= 0;
if(lines_dont_match)return;
while(1){
changing= 1;print_where= 1;change_line++;
if(!input_ln(change_file)){
err_print("! Change file ended before @y");

change_limit= 0;changing= 0;print_where= 1;
return;
}
/*16:*/
#line 338 "common.web"

if(buffer[1]==0151){
loc= buffer+2;
err_print("! No includes allowed in change file");

}

/*:16*/
#line 385 "common.web"
;
/*20:*/
#line 402 "common.web"

if(limit>buffer+1&&buffer[0]==0100){
/*15:*/
#line 333 "common.web"

if(buffer[1]>=0130&&buffer[1]<=0132||buffer[1]==0111)buffer[1]+= 0172-0132;

/*:15*/
#line 404 "common.web"
;
if(buffer[1]==0170||buffer[1]==0172){
loc= buffer+2;err_print("! Where is the matching @y?");

}
else if(buffer[1]==0171){
if(n>0){
loc= buffer+2;
err_print("! Hmm... some of the preceding lines failed to match");

}
return;
}
}

/*:20*/
#line 387 "common.web"
;
/*18:*/
#line 357 "common.web"

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

/*:18*/
#line 388 "common.web"
;
changing= 0;print_where= 1;cur_line++;
while(!input_ln(cur_file)){
if(include_depth==0){
err_print("! WEB file ended during a change");

input_has_ended= 1;return;
}
include_depth--;print_where= 1;cur_line++;
}
if(lines_dont_match)n++;
}
}

/*:19*//*21:*/
?endgroup
\endgroup
\vfill\eject

\def\runninghead{APPENDIX E --- MACROS FOR FORMATTING}
\section Appendix E: The \.{cwebmac.tex} file.
This is the file that extends ``plain \TeX'' format in order to support the
features needed by the output of \.{WEAVE}.

\vskip6pt
\begingroup \def\tt{\eighttt} \baselineskip9pt
\let\?=?
\def\printmacs{\input cwebmac}
\verbatim
?printmacs
?endgroup
\endgroup
\vfill\eject

\narrower
\def\runninghead{APPENDIX F --- NOTES ON FORMATTING}
\section Appendix F: How to use \.{WEB} macros.
The macros in \.{webmac} make it possible to produce a variety of formats
without editing the output of \.{WEAVE}, and the purpose of this appendix
is to explain some of the possibilities.

\def\point#1.{\yskip\indent#1.\quad\ignorespaces}

\point 1. Three fonts have been declared in addition to the standard fonts of
\.{PLAIN} format: You can say `\.{\{\\sc stuff\}}' to get {\sc STUFF}
in small caps; and you can select the largish fonts \.{\\titlefont}
and \.{\\ttitlefont} in the title of your document, where \.{\\ttitlefont}
is a typewriter style of type.

\point 2. When you mention an identifier in \TeX\ text, you normally call
it `\.{|identifier|}'. But you can also say `\.{\\\\\{identifier\}}'. The
output will look the same in both cases, but the second alternative
doesn't put \\{identifier} into the index, since
it bypasses \.{WEAVE}'s translation from \cee\ mode.

\point 3. To get typewriter-like type, as when referring to `\.{WEB}', you
can use the `\.{\\.}' macro (e.g., `\.{\\.\{WEB\}}'). In the argument to
this macro you should insert an additional backslash before the symbols
listed as `special string characters' in the index to \.{WEAVE}, i.e.,
before backslashes and dollar signs and the like.
A `\.{\\\ }' here will result in the visible space symbol; to get an
invisible space following a control sequence you can say `\.{\{\ \}}'.
[The `\.{\\)}' macro is similar to the preceding one, but instead
of putting the string in an hbox it prints it in as many lines as
necessary, with a backslash at the end of all but the last lines.
A space not preceded by a backslash is ignored by this macro.]

\point 4. The three control sequences \.{\\pagewidth}, \.{\\pageheight},
and \.{\\fullpageheight} can be redefined in the limbo section at the
beginning of your \.{WEB} file, to change the dimensions of each page.
The standard settings
$$\lpile{\.{\\pagewidth=6.5in}\cr
  \.{\\pageheight=8.7in}\cr
  \.{\\fullpageheight=9in}\cr}$$
were used to prepare the present report; \.{\\fullpageheight} is
\.{\\pageheight} plus room for the additional heading and page numbers at
the top of each page. If you change any of these quantities, you should
call the macro \.{\\setpage} immediately after making the change.

\point 5. The \.{\\pageshift} macro defines an amount by which right-hand
pages (i.e., odd-numbered pages) are shifted right with respect to
left-hand (even-numbered) ones. By adjusting this amount you may be
able to get two-sided output in which the page numbers line up on
opposite sides of each sheet.

\point 6. The \.{\\title} macro will appear at the top of each page
in small caps. \dots

\point 7. The first page usually is number 1; if you want some other
starting page, just set \.{\\pageno} to the desired number. \dots

\point 8. The macro \.{\\iftitle} will suppress the header line if it is
defined by `\.{\\titletrue}'. The normal value is \.{\\titlefalse}
except for the table of contents; thus, the contents
page is usually unnumbered. If your program is so long that the table of
contents doesn't fit on a single page, or if you want a number to appear
on the contents page, you should reset \.{\\pageno} when you begin the
table of contents.

Two macros are provided to give flexibility to the table of
contents: \.{\\topofcontents} is invoked just before the contents
info is read, and \.{\\botofcontents} is invoked just after.
[Here's a typical definition:]
$$\lpile{\.{\\def\\topofcontents\{\\null\\vfill}\cr
  \.{ { }\\titlefalse \% include headline on the contents page}\cr
  \.{ { }\\def\\rheader\{\\mainfont The \{\\tt WEAVE\}{ }processor\\hfil\}}\cr
  \.{ { }\\centerline\{\\titlefont The \{\\ttitlefont WEAVE\}{ }processor\}}\cr
  \.{ { }\\vskip 15pt \\centerline\{(Version 2.5)\}{ }\\vfill\}}\cr}$$
Redefining \.{\\rheader}, which is the headline for right-hand pages,
suffices in this case to put the desired information at the top of the page.

\point 9. Data for the table of contents is written to a file that
is read after the indexes have been \TeX ed; there's one line of data
for every starred module. [Here's what the
file \.{CONTENTS.TEX} might look like:
$$\lpile{\.{\\Z \{{ }Introduction\}\{1\}\{16\}}\cr
  \.{\\Z \{{ }The character set\}\{11\}\{19\}}\cr}$$
and so on.] The \.{\\topofcontents} macro could
redefine \.{\\Z} so that the information appears in another format.

\point 10. Sometimes it is necessary or desirable to divide the output of
\.{WEAVE} into subfiles that can be processed separately. For example,
the listing of \TeX\ runs to more than 500 pages, and that is enough to
exceed the capacity of many printing devices and/or their software.
When an extremely large job isn't cut into smaller pieces, the entire
process might be spoiled by a single error of some sort, making it
necessary to start everything over.

Here's a safe way to break a woven file into three parts:
Say the pieces are $\alpha$,
$\beta$, and $\gamma$, where each piece begins with a starred module.
All macros should be defined in the opening limbo section of $\alpha$,
and copies of this \TeX\ code should be placed at the
beginning of $\beta$ and of $\gamma$. In order to process the parts
separately, we need to take care of two things: The starting page
numbers of $\beta$ and $\gamma$ need to be set up properly, and
the table of contents data from all three runs needs to be
accumulated.

The \.{webmac} macros include two control sequences \.{\\contentsfile} and
\.{\\readcontents} that facilitate the necessary processing.  We include
`\.{\\def\\contentsfile\{CONT1\}}' in the limbo section of $\alpha$, and
we include `\.{\\def\\contentsfile\{CONT2\}}' in the limbo section of
$\beta$; this causes \TeX\ to write the contents data for $\alpha$ and $\beta$
into \.{CONT1.TEX} and \.{CONT2.TEX}. Now in $\gamma$ we say
$$\.{\\def\\readcontents\{\\input CONT1 \\input CONT2 \\input CONTENTS\}};$$
this brings in the data from all three pieces, in the proper order.

However, we still need to solve the page-numbering problem. One way to
do it is to include the following in the limbo material for $\beta$:
$$\lpile{\.{\\message\{Please type the last page number of part 1: \}}\cr
  \.{\\read-1to\\\\ \\pageno=\\\\ \\advance\\pageno by 1}\cr}$$
Then you simply provide the necessary data when \TeX\ requests
it; a similar construction is used at the beginning of $\gamma$.

This method can, of course, be used to divide a woven file into
any number of pieces.

\point 11. Sometimes it is nice to include things in the index that are
typeset in a special way. For example, we might want to have an
index entry for `\TeX'. \.{WEAVE} provides only two standard ways to
typeset an index entry (unless the entry is an identifier or a reserved word):
`\.{@\^}' gives roman type, and `\.{@.}' gives typewriter type.
But if we try to typeset `\TeX' in roman type by saying, e.g.,
`\.{@\^\\TeX@>}', the backslash character gets in the way,
and this entry wouldn't appear in the index with the T's.

The solution is to use the `\.{@:}' feature, declaring a macro that
simply removes a sort key as follows:
$$\.{\\def\\9\#1\{\}}$$
Now you can say, e.g., `\.{@:TeX\}\{\\TeX@>}' in your \.{WEB} file; \.{WEAVE}
puts it into the index alphabetically, based on the sort key, and
produces the macro call `\.{\\9\{TeX\}\{\\TeX\}}' which will ensure that
the sort key isn't printed.

A similar idea can be used to insert hidden material into module
names so that they are alphabetized in whatever way you might wish.
Some people call these tricks ``special refinements''; others call
them ``kludges''.

\point 12. The control sequence \.{\\modno} is set to the number of the
module being typeset.

\point 13. If you want to list only the modules that have changed,
together with the index, put the command `\.{\\let\\maybe=\\iffalse}' in
the limbo section before the first module of your \.{WEB} file. It's
customary to make this the first change in your change file.
\endnarrower
\vfill\end
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