path: root/Master/texmf-dist/doc/generic/texapi/texapi-doc.tex

\input pitex % which \input's texapi (and YaX)

\setparameter document:
  author   = "Paul Isambert"
  title    = \texapi
  pdftitle = TeXapi
  version  = \texapiversion
  date     = "\the\month/\the\day/\the\year"
  subject  = "The TeXapi documentation."
  display  = outlines

\setparameter page:
  width        = 32cm
  height       = 32cm
  lines        = 46
  hsize        = 10cm
  baselineskip = 14pt
  left         = 10cm
  top          = 5cm
  parindent    = 2em

\setparameter font:
  command = \mainfont
  name    = "Chaparral Pro"
  size    = 12pt
  small = 11pt
  big = 20pt

\setparameter font:
  command = \tcodefont
  name    = "Lucida Console"
  size    = 9.5pt
  bold italic   = none
  features = "space = mono"

\setparameter font:
  command = \cscodefont
  name    = "Lucida Console"
  size    = 8.5pt
  bold italic   = none
  features = "space = mono"

\def\codefont{%
  \ifcslist \cscodefont
  \else \tcodefont\fi}
\def\tcode#1{{\codefont#1}}%

% 
%
% OUTPUT
%
\newbox\codebox
\newdimen\sepdim
\sepdim=1.2pc

\pdfdef\&{&}
\newdimen\originalvsize
\originalvsize=\vsize

\output={%
  \setbox255=\vtop{\unvbox255}
  \setbox\codebox=\vtop{\unvbox\codebox}
  \ht255=\baselineskip
  \ht\codebox=\baselineskip
  \shipout\vbox{%
    \vbox to 0pt{%
      \vss
      \hbox to \hsize{%
        \spaceskip .8em plus .6em minus .3em
        \mainfont\big\sc\descriptiontitle
        \unless\ifx\bookmarktitle\prevbookmarktitle
          \passexpanded{\outline0}{\bookmarktitle}%
        \fi}
      \kern2\baselineskip}%
    \hbox{%
      \box255
      \kern\sepdim
      \pdfliteral{
        q
        .95 g
        -3 200 300 -1000 re f
        Q
      }
      \box\codebox
      }%
    }
  \advancepageno
  \global\let\prevbookmarktitle\bookmarktitle
  \global\vsize=\originalvsize
  }

%
%
% \cslist

\def\red{\color{.9 0 0}}
\def\rcom#1{\red{\com#1}}
\newbox\cslistbox
\newife\ifexpcs
\newif\ifcslist
\newbox\tempbox
\newdimen\tempdimen
\newdimen\cswidth
\newcount\cslistcount
\def\zilch{\zilch}
\extraboxspace=1.5pt
\def\macrobox{\colorbox{.92 .92 .92}}
\def\definecs#1#2{
  \quitvmode
  \hbox  to\cswidth{\iffexpcs\macrobox{\unless\ifx#1\zilch\rcom#1\fi}\hfill}%
  \setcatcodes{/=13}%
  \scantextokens{#2}%
  \restorecatcodes
  }
\def\longdefinecs#1#2\end{\definecs#1{#2}}
\def\getwidth#1#2\end{%
  \bgroup
    \setbox0=\hbox{\codefont\string#1}%
    \ifdim\wd0>\cswidth
      \global\cswidth=\wd0
    \fi
  \egroup
  }
\def\cslist#1{%
  \vskip\baselineskip
  \cslisttrue \cslistcount=0
  \cswidth=0pt
  \dofornoempty{#1,}##1,{%
    \deftrim\temp{##1}%
    \passexpanded{\iffprefix!}{\temp}
             {\passexpanded{\removeprefixin!}{\temp}\temp}%
    \expandafter\getwidth\temp\end
    }{}%
%
  \tempdimen=0pt
  \dofornoempty{#1,}##1,{%
    \advance\cslistcount1
    \deftrim\temp{##1}%
    \passexpanded{\ifprefix!}{\temp}
             {\expcstrue\passexpanded{\removeprefixin!}{\temp}\temp}
             {\expcsfalse}%
    \setbox\tempbox\hbox{\expandafter\longdefinecs\temp\end\kern\sepdim}%
    \ifdim\wd\tempbox>\tempdimen
      \tempdimen=\wd\tempbox
    \fi
    }{}%
%
  \setbox\cslistbox=\vtop{%
    \dofornoempty{#1,}##1,{%
      \deftrim\temp{##1}%
      \passexpanded{\ifprefix!}{\temp}
               {\expcstrue\passexpanded{\removeprefixin!}{\temp}\temp}
               {\expcsfalse}%
      \llap{\hbox to\tempdimen{\expandafter\longdefinecs\temp\end\hfil}}%
      }{}%
    }%
  \dp\cslistbox=0pt
  \noindent \box\cslistbox
  \def\par{%
    \endgraf
    \let\par\endgraf
    \ifnum\prevgraf<\cslistcount
      \vskip\the\numexpr(\cslistcount-\prevgraf)\baselineskip
    \fi}%
  \cslistfalse \ignorespaces
  }
%
\bgroup
\setcatcodes{/=13}
\gdef/#1/{\arg{#1}}
\egroup

\def\true{\arg{true}}
\def\false{\arg{false}}
\def\csarg{\arg{csname}}
\def\comarg{\arg{command}}


%
% EXAMPLES
%

\newverbatim\example{\codefont\parindent0pt}
                     {\vskip\baselineskip\printverbatim\relax
                      \vskip\baselineskip\removenextindent}
\newverbatim\Example{}{%
  \global\setbox\codebox=\vbox{%
    \parindent0pt
    \ifvoid\codebox
      \quitvmode\vrule height \topskip depth 0pt width 0pt
    \else
      \dimen0=\dp\codebox
      \box\codebox
      \vskip\baselineskip
      \color{1 1 1}{\hrule width \hsize height 1pt depth 1pt}%
      \kern-2pt
      \vskip\baselineskip
      \prevdepth=\dimen0
    \fi
    \let\exampleskip\relax
    \cslisttrue \codefont
    \overfullrule=0pt
    \printverbatim
    \vskip\baselineskip
    \mainfont\small
    \doverbatim
    }%
  }

\newblock\description
  {\getdescriptiontitle}
  {\penalty-10000\relax}

\def\getdescriptiontitle#1{%
  \def\bookmarktitle{#1}%
  \def\descriptiontitle{}%
  \dofor{#1 }##1 {%
    \dofor{##1}####1{%
      \addright\descriptiontitle{\lowercase{####1}\hskip0pt plus 8pt minus 2pt}%
      }{}%
    \addright\descriptiontitle{\unskip\spacecs}%
    }{}%
  \addright\descriptiontitle{\unskip}%
  }
\def\texapi{%
  {\codefont texapi}%
  \antigobblespace
  }

\overfullrule=0pt



\description{Writing macros with texapi}

\setbox\codebox=\vbox to \hsize{%
  \small
  \hfill \vrule height\topskip width0pt Author: \usevalue document : author \par
  \hfill Version: \usevalue document : version \par
  \hfill Date: \usevalue document : date \par
  \vskip\baselineskip
  \noindent Typeset in Chaparral Pro (Carol Twombly)
  and Lucida Console\hfil\penalty-10000 (Charles Bigelow and Kris Holmes)
  with Lua\TeX\ v.\directlua{tex.print(tex.luatexversion/100)}.

  }

The first motivation for this set of macros is selfish:
after rewriting the same lines over and over and wasting
so many excruciating (yes!) hours debugging intricate loops
with one typo, I decided I could use a toolkit containing
the painful code without errors (hopefully) and use it
for future packages.

The second motivation is more ambitious: I think it's a pity
so many packages are written for one format and are thus
unusable outside it, even though those packages could be useful
to anybody. This is so, I believe, because a format mixes two
different things: decisions about typesetting (mainly) and utility macros.
The former are the essence of a format, whereas the latter are just
shorthands you can use or not, replace, or ignore completely.
But the fact is that users of a format tend to use the utility macros
shipped with it, and thus writes macros that can't be reused elsewhere,
even though nothing crucial hinges on what utility macros one uses.
Thus, \texapi aims at providing a good deal of this kind of macros
whitout relying on any particular format, so that one can write
code without having to take into account how it will be used.
Moreover, \texapi is also format-aware, meaning some commands
are defined differently depending on the format being used,
and one doesn't have to create as many macros as there are formats.

There is at least one basic assumptions, namely that formats
should contain plain \TeX's allocation macros. This the case for
all formats I know.

\vskip\baselineskip
In what follows, commands have a \macrobox{grey background} when they
are fully expandable, e.g. they can be used inside \com\csname...\com\endcsname,
provided you don't use them with unexpandable arguments, of course.
On the other hand, all unexpandable commands are protected.

Arguments are denoted by \arg{text}, where `text' makes the intended use
clearer and doesn't denote any particular type of argument, except in
the case of \comarg, which denotes a control sequence (something expandable,
actually), and \csarg, which denotes an argument suitable to \com\csname.
Braces are indicated only when mandatory, but of course they can be used to delimit
arguments as usual.

\vskip\baselineskip
Finally, the following may be a useful indication (added in version 1.01).

\vskip-\baselineskip
\cslist{
  \texapiversion
  }
This a macro that holds \texapi's version number.
The current version is \texapiversion.

\description/



\description{Engine and format detection}

\cslist{
  \texenginenumber
  }
This is a \com\chardef'ined number set according to the
engine used: 0 means e-\TeX, or an unknown engine with
e-\TeX\ extensions; 1 means Xe\TeX\ (detected because
\com\XeTeXinterchartoks exists); 2 means pdf\TeX\ (detected
thanks to \com\pdfstrcmp); 3 means Lua\TeX\ (detected thanks
to \com\directlua). Numbering here allows one to detect a
pdf\TeX-based engine with \com\texenginenumber>1. Con\TeX t
has an equivalent \com\texengine, with pdf\TeX=1 and Xe\TeX=2,
though.

\cslist{
  \formatnumber
  }
This number does the same with formats. Here, 0 means an unknown
format, 1 means plain (because \com\fmtname is `\tcode{plain}'),
2 means eplain (because \com\fmtname is `\tcode{eplain}'),
3 means Con\TeX t (because there exists an \com\inspectnextoptionalcharacter
command), 4 means La\TeX2e (because \com\fmtname is `\tcode{LaTeX2e}')
and 5 means La\TeX3 (because there exists an \com\ExplSyntaxOn command).
There's no distinction yet between La\TeX3 on top of La\TeX2e and La\TeX3
as a format per se. Since \com\formatnumber is set only if it doesn't
already exist, you can write your package with, say, \tcode{code.tex}
containing the main code and \tcode{code.sty} and \tcode{t-code.tex}
as wrapper files for La\TeX\ and Con\TeX t respectively, with \com\formatnumber
already set accordingly.

\Example
\def\myengine{%
  \ifcase\texenginenumber
    e-\or Xe\or pdf\or Lua\fi\TeX 
  }
\def\myformat{%
  \ifcase\formatnumber
    unknown\or plain\or eplain\or
    ConTeXt\or LaTeX\or LaTeX3\fi
  }
This documentation has been typeset
with \myformat\ under \myengine.
\Example/

\cslist{
  \priminput,
  \primunexpanded
  }
Both La\TeX\ and Con\TeX t redefines \com\input, and in Con\TeX t
\com\unexpanded has not the meaning of the e-\TeX\ primitive. These
two commands are thus the primitive \com\input and \com\unexpanded
respectively.

\cslist{
  \loadmacrofile/file/
  }
The behavior of this command depends on \com\formatnumber. The \arg{file}
should be given without extension, and the following happens: in Con\TeX t,
\com\usemodule\tcode{[\arg{file}]} is executed, in La\TeX\ \com\RequirePackage\barg{file}
is used, and in other formats it is simply \com\input\arg{file}\tcode{.tex}.
This makes sense only with packages that are distributed as described above,
i.e. with the main code in one file and wrapper files for La\TeX\ and Con\TeX t,
like Ti\ital{k}Z or \ital{librarian}.

\cslist{
  \senderror/package//message/
  }
This sends an error message according to the format's custom. In \tcode{plain}
and \tcode{eplain} (and in an unknown format), it produces
\tcode{\com\errmessage\string{\arg{package} error: \arg{message}\string}}.  In
La\TeX, it produces
\com\PackageError\barg{package}\barg{message}{\codefont\string{\string}} (no
help message) and in Con\TeX t \tcode{\com\writestatus\string{\arg{package}
error\string}}\barg{message} (which is far from Con\TeX t's sophisticated
communication system but, well...).

\description/







\description{Argument manipulation}

\cslist{
  !\emptycs,
  !\spacecs,
  \spacechar
  }
Pretty useful macros whose meaning is clear, but whatever: \com\emptycs is
an emptily defined command, \com\spacecs expands to a space, and \com\spacechar
denotes a space, i.e. it is an implicit space and not really a macro.

\cslist{
  !\gobbleone,
  !\gobbleoneand/code/
  }
Those, as you might imagine, gobble the following argument; the second version
also excutes \arg{code} afterwards. There are actually nine
such commands in each case, and they are (for the sake of completeness)
\com\gobbleone, \com\gobbletwo, \com\gobblethree, \com\gobblefour,
\com\gobblefive, \com\gobblesix, \com\gobbleseven, \com\gobbleeight\
(watch out, two \ital{e}'s) and \com\gobblenine for the first version,
and \com\gobbleoneand, \com\gobbletwoand, \com\gobblethreeand,
\com\gobblefourand, \com\gobblefiveand, \com\gobblesixand,
\com\gobblesevenand, \com\gobbleeightand and \com\gobblenineand. Note
that \com\gobblenineand\arg{code} takes two expansion steps to
return \arg{code}, instead of only one in the other cases.

\Example
This is \gobbletwoand{very } uninteresting.
\Example/

\cslist{
  !\unbrace/code/
  }
This is the kind of command you probably can't see the point of until
you need it. It returns its \arg{code} untouched, but with outermost
braces removed if any.

\cslist{
  !\swapargs/arg1//arg2/,
  !\swapbraced/arg1//arg2/,
  !\swapleftbraced/arg1//arg2/,
  !\swaprightbraced/arg1//arg2/
  }
The first of those returns \arg{arg2}\arg{arg1} into the stream, without
any brace to delimit them.
On the contrary, \com\swapbraced returns \barg{arg2}\barg{arg1}. And, as
you might imagine, \com\swapleftbraced returns
\barg{arg2}\arg{arg1} whereas \com\swaprightbraced returns \arg{arg2}\barg{arg1}.

\cslist{
  !\passexpanded/arg1//arg2/,
  !\passexpandednobraces/arg1//arg2/
  }
The first one returns \arg{arg1}\barg{arg2 expanded once} and the second
\arg{arg1}\arg{arg2 expanded once}. It's some sort
of long \com\expandafter built on \com\swapargs and associates,
and if \arg{arg1} is a single token it's faster to use \com\expandafter
itself. It's not a real \com\expandafter, though, since \arg{arg2} is
expanded to the left of \arg{arg1} and then moved back to its
right. Which, with e.g. an \com\else as \arg{arg2}, will lead
to results you probably haven't foreseen and expected.
If \arg{arg2} is some material you want to turn into a command with
\com\csname, see \com\passcs below.

\Example
\def\foo#1#2{\detokenize{(1=#1,2=#2)}}
\def\bar{two}
\foo{one}\bar
\passexpanded{\foo{one}}\bar
\Example/

\description/









\description{Defining \& using commands}

\cslist{
  \defcs\csarg/parameter text/\barg{definition},
  \edefcs\csarg/parameter text/\barg{definition},
  \gdefcs\csarg/parameter text/\barg{definition},
  \xdefcs\csarg/parameter text/\barg{definition}
  }
These work exactly like \com\def, \com\edef, \com\gdef
and \com\xdef, except they define a command with name
\csarg. The \arg{parameter text} is the usual one,
and any the space at the beginning is significant. I.e.
\verb/\defcs{foo}#1{...}/ and \verb/\defcs{foo} #1{...}/
aren't equivalent at all. Prefixes can be appended as with
\com\def.

\Example
\defcs{foo}#1{This is foo: #1.}
\foo{bar}
\Example/


\cslist{
  \letcs\csarg\comarg,
  \lettocs\comarg\csarg,
  \letcstocs\csarg\csarg
  }
These \com\let the first command or command named \csarg\ to
the meaning of the second one. In both \com\lettocs and \com\letcstocs,
if the command with name \csarg\ is undefined, it is not let to \com\relax.
So these are different from \com\let with \com\expandafter's. The \com\letcs
command can also be used to create an implicit character, of course.

\Example
\expandafter\let\expandafter\foo
                \csname undefined\endcsname
\lettocs\bar{reallyundefined}
\letcstocs{reallyundefined}{reallyundefined}

Compare this: \meaning\foo,
and that: \meaning\bar.
And better yet: \meaning\reallyundefined.
\Example/


\cslist{
  \addleft\comarg/material/,
  \addleftcs\csarg/material/,
  \eaddleft\comarg/material/,
  \eaddleftcs\csarg/material/
  }
This redefines \comarg\ or a command named \csarg\ to
itself with \arg{material} added at the beginning. The e-variant
performs an \com\edef so that \arg{material} is fully expanded
(but not \comarg). The usual prefixes can be appended.

\cslist{
  \addright\comarg/material/,
  \addrightcs\csarg/material/,
  \eaddright\comarg/material/,
  \eaddrightcs\csarg/material/
  }
This is the same thing as above, but the material is added 
at the end. In both the left and right version, the command
thus redefined should be a simple command working by itself
(i.e. no argument and no delimiter). In the \csarg\ case,
no check is performed to ensure that \csarg\ is defined
(but in the worst case it ends up as \com\relax, because of
its being called after the implicit \com\def\ (get it?)).

\Example
\defcs{foo}{bar}
\addleftcs{foo}{In a }
\addright\foo{ (how fascinating).}
\foo
\Example/

\cslist{
  !\usecs\csarg,
  !\usecsafter\csarg,
  !\passcs/code/\csarg,
  !\passexpandedcs/code/\csarg,
  \noexpandcs\csarg,
  \unexpandedcs\csarg
  }
Various ways to use a command with name \csarg:
\com\usecs performs a simple \com\csname\csarg\com\endcsname\
(and doesn't even check whether \csarg\ is defined or not, so
this might relax it a little bit), \com\usecsafter does the equivalent
of \com\expandafter\com\command, \com\passcs puts \csarg\ as a real
(unbraced) command after \arg{code}, whereas \com\passexpandedcs passes
the expansion of the control sequence with name \csarg\ to \arg{code}; \com\noexpandcs and \com\unexpandedcs
return \csarg\ with a \com\noexpand prefix or its expansion as argument to
\com\unexpanded\ (\com\primunexpanded, really).

\Example
\def\bar{whatever} \def\foo#1{[#1]}
I use it: \usecs{bar}, 
I use it after: \usecsafter{foo}\bar,
and I pass it: \passcs\foo{bar}.
\Example/
\Example
\def\foo{\bar}
I don't expand it:
\edef\foobar{\noexpandcs{foo}}%
\meaning\foobar.
Or just a little bit:
\edef\foobar{\unexpandedcs{foo}}%
\meaning\foobar.
\Example/

\cslist{
  !\commandtoname\comarg
  }
This returns the name of \comarg, i.e. \comarg\ without its backslash
(and made of catcode-12 characters, since it's based on \com\string).

\description/









\description{Tests with commands}

\cslist{
  !\reverse
  }
Conditionals in \texapi\ (not only those on this page) can be prefixed with
\com\reverse, so that if they're true the \false\ argument is executed (if
specified), and if they're false, the \true\ argument is executed. So this is
equivalent to \com\unless, to which \com\reverse defaults (since version
1.04) in case the following command isn't recognized as a \texapi conditional.

\Example
\reverse\iffalse
  Wow, \verb"\reverse" can replace \verb"\unless"!
  We must be using version 1.04 at least!
\fi
\Example/

\cslist{
  !\ifcommand\comarg\true\false,
  !\iffcommand\comarg\true
  }
This conditional executes \true\ if \comarg\ is defined.
So it is a straight version of \com\ifdefined. The \com\iff...
version, like all \texapi's \com\iff..., considers only the
\true\ case (which becomes the \false\ case if the conditional
is prefixed with \com\reverse).

\Example
\ifcommand\TeX{Cool}{Too bad}.
Nothing: \iffcommand\undefined{Whatever}.
\Example/

\cslist{
  !\ifcs\csarg\true\false,
  !\iffcs\csarg\true
  }
Same as above, but with an \com\ifcsname this time.
It goes without saying that \csarg\ isn't let to \com\relax
thereafter if it was undefined.

\Example
\reverse\iffcs{undefined}{This command is undefined.}
\Example/

\cslist{
  !\ifemptycommand\comarg\true\false,
  !\iffemptycommand\comarg\true
  }
This is true if \comarg\ is defined with an empty
definition text, i.e. it is equivalent to \com\emptycs.
This is not true if \comarg\ takes arguments, though,
so \com\gobbleone isn't empty in this sense.

\cslist{
  !\ifemptycs\csarg\true\false,
  !\iffemptycs\csarg\true
  }
Same as above with a command named \csarg.

\Example
\def\foo{}
\ifemptycommand\foo{Empty}{Not empty}.
\reverse\iffemptycs{gobbleone}{It ain't empty}.
\Example/



\cslist{
  !\ifxcs\csarg\comarg\true\false,
  !\iffxcs\csarg\comarg\true
  }
This is true if \csarg\ has the same definition as \comarg,
or they're both undefined.

\cslist{
  !\ifxcscs\csarg\csarg\true\false,
  !\iffxcscs\csarg\csarg\true
  }
This is true if both \csarg's have the same definition,
or they're both undefined.

\Example
\iffxcs{undefined}\undefinedtoo
       {Same definitions.}
\ifxcscs{foo}{TeX}
        {These are the same}
        {These are different}.
\Example/

\description/










\description{Various conditionals}

\cslist{
  \newife\comarg
  }
This defines a conditional like plain \TeX's \verb/\newif/,
except it takes two arguments (the \true\ and \false\ values)
instead of an \com\else ... \com\fi structure. Besides,
this conditional is reversible with \com\reverse, and
a `double-f\kern1pt' (i.e. \com\iff...) version is also created,
which takes the \true\ part only. As with
\verb/\newif/, \comarg\ must begin with \tcode{if}.
(The \ital{e} means \ital{expandable}, although there's
nothing more expandable in the conditionals thus constructed
than in those defined with \verb/\newif/, but anyway.)

\Example
\newife\iffoo
\iffoo{There is foo}{There is no foo}.
\footrue
\reverse\iffoo{There is no foo}{There is foo}.
\ifffoo{With three f's in a row}.
\Example/

\cslist{
  !\straightenif/\TeX\ conditional//arg/\true\false,
  !\straighteniff/\TeX\ conditional//arg/\true
  }
Apart from \com\ifdefined and \com\ifcsname\ (in the guise
of \com\ifcommand and \com\ifcs respectively), none of \TeX's
primitive conditionals are redefined in a straight fashion,
i.e. with two arguments instead of \com\else ... \com\fi.
These commands let you use \TeX's conditionals in such a way.
\arg{\TeX\ conditional} means such a primitive without a
backslash (so this construction can be used inside real
conditionals), e.g. \tcode{ifnum} or \tcode{ifvoid}.
The \arg{arg} is whatever you normally feed to this conditional.
It is brutally concatenated, and you're the one in charge
of adding space if needed, as for instance with \tcode{ifnum}.
Chaos will ensue if you fail to do so. With conditionals that don't
require anything, e.g. \tcode{iftrue} or \tcode{ifvmode},
leave \arg{arg} empty (but don't forget it).
Finally, \true\ and \false\ are executed accordingly, and the
whole macro can be prefixed with \com\reverse.

\Example
                       % See this space?
\straightenif{ifnum}{1=1 }{Reality is preserved}
                          {Bad news}.
\reverse\straighteniff{if}{ab}
             {Different letters, obviously.}
\straightenif{iftrue}{}{Good}{Bad}.
\Example/

\cslist{
  !\ifwhatever/conditional/\true\false,
  !\iffwhatever/conditional/\true
  }
This command (introduced in v.1.04) takes a \arg{conditional} which is
either a \TeX\ conditional (normally expecting \com\fi and perhaps \com\else
before that) or a conditional whose \true\ and \false\ parts are normally
given as arguments, like those created by \com\newife. In the first case, it
is equivalent to \com\straightenif, in the second case it is redundant.
However, it is useful when one is expecting a conditional whose nature is
unknown. If \arg{conditional} is a \TeX\ conditional, you're in charge of
adding space if needed, as with \com\straightenif; unlike the latter, though,
the \com\if... command itself is given as usual (i.e. no need to remove the
backslash), which also means it cannot be properly nested in a \TeX\
conditional (unless itself is embedded in \com\straightenif). Finally, if
\arg{conditional} is an argument-taking conditional, the \tcode{iff} form (in
case it comes from \texapi) cannot be used, and conditionals poking at the
next token cannot be used either. The whole macro can be prefixed with
\com\reverse.

\Example
                    % See this space too?
\ifwhatever{\ifnum5=5 }{True.}{False.}
\newife\iftest
\reverse\iffwhatever\iftest{True too.}
\Example/

\description/





\description{Conditional expressions}

\cslist{
  !\ifexpression/expression/\true\false,
  !\iffexpression/expression/\true
  }
This (introduced in v.1.04) evaluates \arg{expression}, which is made of
subexpressions separated by \com& (and) or \com| (or), a subexpression being
either a conditional or a braced expression, possibly prefixed with \com-
(not). The `not' operator has precedence over `and', which has precedence over
`or', braces being used to group evaluation. The conditionals making up the
expressions are the same as those passed to \com\ifwhatever (which is used
internally), i.e. \TeX\ conditionals or argument-taking ones. Space is ignored
at the beginning of an operand, but not at the end, unless the operand is a
braced expression. However, such a space is often harmless there (if the
conditional is a \texapi conditional), and sometimes useful (to delimit for
instance a number in an \com\ifnum, see the example on the right); it should be
removed in the usual cases (e.g. after \com\ifcat\ \tcode{XY}). The macro can
be prefixed with \com\reverse.

\Example
\def\iffibonacci#1{%
  \ifexpression{%
    -\ifnum#1<0 & -\ifnum#1>100 &
    { \ifnum#1=0  | \ifnum#1=1  |
      \ifnum#1=2  | \ifnum#1=3  |
      \ifnum#1=5  | \ifnum#1=8  |
      \ifnum#1=13 | \ifnum#1=21 |
      \ifnum#1=34 | \ifnum#1=55 |
      \ifnum#1=89 }
    }{#1 is a Fibonacci number lower than 100.}
     {#1 isn't a Fibonnaci number lower than 100.}%
  }

\iffibonacci{55}
\Example/

In the example on the right, the first two conditionals (excluding negative
numbers and numbers lower than 100) are logically useless, but they save time
(the third subexpression isn't evaluated in case one of the first two is
true), and they illustrate how negation and grouping work.



\cslist{
  !\ifelseif/statements/
  }
This (introduced in v.1.04) is a simple way to evaluate successive
conditionals until one is found true; the \arg{statements} are any number of
pairs \arg{conditional}\arg{statement}; when the first true \arg{conditional}
is found, its associated \arg{statement} is executed and the rest is
discarded. The conditionals there are the same as with \com\ifwhatever. The
macro can be prefixed with \com\reverse, in which case the statement
associated with the first false conditional is executed. If no conditional is
true (or false, if \com\reverse is used), nothing happens; a default case can
nonetheless be constructed with a last statement whose conditional is
\com\iftrue (or \com\iffalse with \com\reverse), as illustrated in the example
on the right. Spaces are ignored.

The construction is the same thing as embedding each conditional into the
\false\ part of the previous one; however, it is simpler to write and to read.

\Example
\def\checkanswer#1{%
  \ifelseif{%
    {\ifexpression{ \ifstring{#1}{yes} | 
                    \ifstring{#1}{true}} }
      {You agree.}
    {\ifexpression{ \ifstring{#1}{no} |
                    \ifstring{#1}{false}} }
      {You disagree.}
    \iftrue
      {I don't understand your answer.}}%
  }

+\checkanswer{You bet!}+
\Example/


\cslist{
  !\afterfi/code/,
  !\afterdummyfi/code/
  }
You shouldn't use these. The first one closes the current conditional and
executes \arg{code}. The second one lets go one \com\fi and executes
\arg{code}. So these are kinds of \com\expandafter's when \arg{code} isn't
just a command. Anything before the incoming \com\fi is gobbled. The reason
why you should use one or the other should be clear to you, otherwise you'll
probably be messing with a conditional.

\Example
\iftrue
  \afterdummyfi{\afterfi{Here we are.}}
\else
  \iffalse
    Whatever.
  \fi
\fi
\Example/

\description/








\description{Poking at what comes next}

\cslist{
  \skipspace/code/
  }
This gobbles any incoming space, if any, and executes \arg{code}.
Of course it doesn't require there to be any space to work properly.
(This was called \com\nospace prior to version 1.02.)

\vskip\baselineskip

All the following conditionals can be prefixed with \com\reverse.
And in case your head's buzzing, their names are quite regular:
take an \com\if, \com\ifcat or \com\ifx, add `\tcode{next}', and create
variants by doubling the \tcode{f} and/or adding \tcode{nospace}
at the end.

\Example
\skipspace{foo} bar
\Example/

\cslist{
  \ifnext/token/\true\false,
  \iffnext/token/\true,
  \ifnextnospace/token/\true\false,
  \iffnextnospace/token/\true
  }
These poke at the next token and see whether it
has the same character code as \arg{token}. In other
words, an \com\if test is performed between \arg{token}
and the next token in the input stream. However, neither
\arg{token} nor the incoming token are expanded, so that
they can be control sequences and no unwanted expansion 
will occur. Control sequences are all equal according to
this test (which can very well take an undefined control
sequence as \arg{token}). The nospace version must be
pretty clear: the macro discards all incoming spaces until
it finds a non-space token to test (unfortunately,
an implicit space and a space character are undistinguishable
as far as this test (and the next ones) is concerned, so in
the very unlikely case where an implicit space was waiting
in the stream, it'll be gobbled in the nospace variant).

\Example
Here comes \ifnext e{an }{a }e.
Here comes \reverse\ifnext e{a }{an }b.
Here comes
\iffnextnospace\foo{a control sequence: } \TeX.
\Example/

\cslist{
  \ifcatnext/token/\true\false,
  \iffcatnext/token/\true,
  \ifcatnextnospace/token/\true\false,
  \iffcatnextnospace/token/\true
  }
These are the same as above with an \com\ifcat test
instead of \com\if. Again, control sequences aren't expanded
and they all have the same category code.

\Example
\def\tex{\TeX\iffcatnext a{ }}
A \tex is a \tex is a \tex.
\Example/

\cslist{
  \ifxnext/token/\true\false,
  \iffxnext/token/\true,
  \ifxnextnospace/token/\true\false,
  \iffxnextnospace/token/\true
  }
Once again like the previous commands, this time with
an \com\ifx, i.e. the definitions of control sequences
are compared, and in case \arg{token} and/or the next
token are unexpandable thing, both character code and
category code are compared. So these are performing 
real \com\ifx tests.

\Example
\def\foo{not \string\TeX}
\reverse\iffxnextnospace\TeX
  {The incoming command isn't \string\TeX: } \foo.
\Example/

\description/






\description{String manipulation}

\cslist{
  !\ifstring/string1//string2/\true\false,
  !\iffstring/string1//string2/\true
  }
These return \true\ if the two strings are identical.
Category codes aren't taken into account when strings
are compared.

\Example
Two \ifstring{abc}{abc}{equal}{unequal} strings
and an \reverse\iffemptystring{something}{unempty} one.
\Example/


\cslist{
  !\ifemptystring/string/\true\false,
  !\iffemptystring/string/\true
  }
These return \true\ if \arg{string} is empty.




\cslist{
  \newstring/string/
  }
The following operations (\com\ifprefix, \com\removesuffix, etc.)
aren't fully expandable by default. However, if a string has been
previously declared with \com\newstring, they magically become
fully expandable.

So, in what follows, macros aren't marked as expandable, although
they can be if the preceding condition is fulfilled. Besides, these
macro aren't \com\protected even though their default behavior would
require that they be. But you can always append a \com\noexpand to
an unprotected command, whereas you cannot force the execution of a
protected one. (This protecting issue is of course totally irrelevant
for the \com\removeprefixin and \com\removesuffixin commands, which aren't
expandable by definition and are thus protected.)




\cslist{
  \ifprefix/prefix//string/\true\false,
  \iffprefix/prefix//string/\true
  }
This test is true if \arg{string} begins with \arg{prefix}.
Category codes do matter. 

\Example
\newstring{abc}
\edef\foo{\ifprefix{abc}{abcd}{True}{False}.}
\edef\bar{\reverse\iffsuffix{abc}{whatever}{No suffix}.}
\edef\foobar{\ifcontains{abc}{gee}{Yes}{No}.}
\meaning\foo\par
\meaning\bar\par
\meaning\foobar
\Example/

\cslist{
  \ifsuffix/suffix//string/\true\false,
  \iffsuffix/suffix//string/\true
  }
True if \arg{string} ends with \arg{suffix}.

\cslist{
  \ifcontains/string1//string2/\true\false,
  \iffcontains/string1//string2/\true
  }
Finally, this is true if \arg{string2} contains \arg{string1}.


\cslist{
  \removeprefix/prefix//string/,
  \removesuffix/suffix//string/
  }
These return \arg{string} without \arg{prefix} (resp.
\arg{suffix}). No test is performed to check that
\arg{string} indeed begins (resp. ends) with \arg{prefix}
(resp \arg{suffix}), so these macros make sense only after
the adequate tests.

\cslist{
  \removeprefixand/prefix//string//code/,
  \removesuffixand/suffix//string//code/
  }
These do the same as the previous one, but feed the
resulting string to \arg{code}, between braces. Once again,
no test is performed beforehand.

\cslist{
  \removeprefixin/prefix//string/\comarg,
  \removesuffixin/suffix//string/\comarg
  }
These define \comarg\ as \arg{string} without \arg{prefix}
(resp. \arg{suffix}). No test either. Sorry.

\cslist{
  \splitstringat/string1//string2//code/
  }
This cuts \arg{string2} in two at \arg{string1}'s first occurrence 
and passes the two parts as braced arguments to \arg{code}. And,
again: no test. (This was called \com\splitstring prior to version
1.02.)

\Example
\def\record#1 : #2.{%
  \par\bgroup
    \it\ifprefix*{#1}{\removeprefix*{#1} [live]}{#1}
  \egroup
  (\ifcontains/{#2}{\splitstringat/{#2}{\dodate}}{#2})
  }
\def\dodate#1#2{recorded #1, released #2}

A somewhat incomplete list of fantastic
records by Frank Zappa:
\record Absolutely Free : 1967.
\record The Grand Wazoo : 1972.
\record L\"ather : 1977/1996.
\record *Make a Jazz Noise Here : 1988/1991.
\Example/

\description/






\description{Various things on the same page}

\cslist{
  \setcatcodes\barg{list}
  }
The \arg{list} argument here means comma separated
\arg{characters}\verb/=/\arg{category code}, with
an \ital{s} to \ital{characters} because you can
concatenate them if you want them to share the same
\arg{category code}. So, as you might have guessed,
this set all \arg{characters} to characters with
catcode \arg{category code}. And it also sets 
\com\restorecatcodes accordingly. The changes are
local. The \verb/#/ character requires a backslash
(so do braces and the backslash itself, but that's obvious).

\cslist{
  \restorecatcodes
  }
This restores the catcodes of the characters changed
with the previous command, which is cumulative, i.e.
\com\restorecatcodes restores catcodes changed by all preceding
\com\setcatcodes commands, not only the last one. Since
changes are local, \com\restorecatcodes may be useless in a group
(and the effect of \com\restorecatcodes itself is local too).

\Example
\setcatcodes{\\\#\{\}\%=12,\|=0}
Hey, were're verbatimizing:
\def\foo#1{\bar{#1}}%
|restorecatcodes
\Example/

\Example
\bgroup
And now in a group:\par
\setcatcodes{z=13}
\defz{ZZZZZZZZZZZZZZZZZZZZZZZZZZ}
I'm sleeping: z.\par
\egroup
And I'm not: z.
\Example/



\vskip\baselineskip
The trimming macros below are adapted from Will Robertson's \tcode{trimspace}
package. Note that trimming on the right is dangerous for braces:
\verb"\trimright{{hello} }" and \verb"\trimright{{hello}}" both result in
\verb"hello", not \verb"{hello}".


\cslist{
  !\trimleft/string/,
  !\trimright/string/,
  !\trim/string/
  }
These return \arg{string} with one space removed at the beginning
or end or both. There's no need to check beforehand whether there
are indeed such spaces.

\Example
+\trim{ bar }+
\Example/

\cslist{
  !\passtrimleft/string//code/,
  !\passtrimright/string//code/,
  !\passtrim/string//code/
  }
These return \arg{string} trimmed of spaces as a braced argument to
\arg{code}.

\cslist{
  \deftrimleft\comarg/string/,
  \deftrimright\comarg/string/,
  \deftrim\comarg/string/
  }
The same thing again, except now those commands define \comarg\
to \arg{string}, etc.

\Example
\deftrimleft\foo{ bar }
+\foo+
\Example/

\description/







\description{While statements}

\cslist{%
  !\repeatuntil/number//code/
  }
This executes \arg{code} \arg{number} times. The \arg{number}
argument can be a \com\count register, an integer defined with
\com\chardef, etc., and of course a string of digits. In any case,
it is really an argument and must be surrounded by braces if it is
made of more than one token.

\Example
We have seen \repeatuntil\pageno{I} pages.\par
\edef\foo{\repeatuntil3{.}}
\meaning\foo
\Example/


\cslist{
  !\dowhile/condition//code/
  }
This repeats \arg{code} while \arg{condition} is true. The latter
must be a `straight' \tcode{if}, i.e. either one of \texapi's
\com\if... or a \com\straightenif\barg{\TeX\ conditional} construction,
in both cases without the \true\ and \false\ arguments, because \true\ is actually
\arg{code}, and \false\ would make no sense. Finally, the conditional
must be a simple \com\if..., not an \com\iff... version. Once again, this
makes sense: the \ital{if and only if} clause is implicit in a \ital{while}
statement. If you use an \com\iff..., you'll end up with many empty braces,
which is harmless unless you're in a context of expansion. You can use \com\reverse
in \arg{condition}.

\Example
\newife\ifbreakloop \def\foo{}
\dowhile{\reverse\ifbreakloop}
        {\addleft\foo{a}%
         \passexpanded\iffstring\foo{aaaa}
                      \breaklooptrue}
\foo
\Example/

\Example
\edef\foo{%
  The inconvenience of iff...:
  \dowhile{\straighteniff{ifnum}{4=5 }}
          {whatever}
  }
\meaning\foo
\Example/



\cslist{
  \newwhile\comarg/number//transformations//code/
  }
The \com\dowhile macro is not very powerful since
you must generally change something somewhere to make
it stops, and thus its expandability is somewhat perfunctory.
That's why there is \com\newwhile. It creates an expandable \comarg\ which takes
\arg{number} arguments (up to 9, as usual) and repeats \arg{code}
indefinetely. So, at first sight, it's bad news. But the point
is \arg{code} is supposed to launch the \com\breakwhile macro below sooner or
later, i.e. stop the loop. Besides, on each iteration (barring the first), \arg{transformations}
are applied to the arguments, and this means: the first argument is
replaced by the first transformation, the second argument by the second
transformation, etc. So there must be as many transformations as there
are arguments, transformations themselves being just code that can
make reference to the arguments. If you don't want to transform an
argument, just repeat it in the transformation.

\cslist{
  !\breakwhile/code/
  }
This breaks the current while loop and executes \arg{code}, which can make
reference to the arguments of the loop.

\cslist{
  !\changewhile/new arguments/
  }
This replaces the default \arg{transformations} defined with \com\newwhile
and passes the \arg{new arguments} for the next iteration. There
must be as many arguments as required by the loop. The original
\arg{transformations} remain in force for the next iterations.

\Example
                        % Transformations.
\newwhile\largestsquare2{\numexpr(#1+1)}{#2}{%
  \reverse\straighteniff{ifnum}{\numexpr(#1*#1)<#2 }
                     {The largest number whose square
                      is smaller than #2 is
                      \breakwhile{\the\numexpr(#1-1).}}}
\largestsquare{1}{50}\par
\largestsquare{1}{200}
\Example/


\description/




\description{For statements on the fly}

\cslist{
  \dofor/list//parameter text/\barg{definition}/coda/
  }
This runs \arg{definition} on each occurrence of 
\arg{parameter text} in \arg{list}. The \arg{parameter text}
is a real one, hence the braces around \arg{definition}.
The \arg{coda} is executed if and only if the loop goes
to its natural end, i.e. it is not terminated by one of
the commands below. It must be present, even if you don't
want one (in which case, leave it empty), and it can't make
any reference to the arguments of the parameter text.
A loop thus executed is absolutely
not expandable. You can embed as many loops as you want
(but don't forget to double the \verb/#/).

\cslist{
  \dofornoempty
  }
This is the same as above, except \arg{definition} is not executed
when the \ital{first} argument is empty.


\cslist{
  \breakfor/code/
  }
This breaks the current loop and executes \arg{code};
the \arg{coda} of the loop is not executed.

\cslist{
  \retrieverest/code/
  }
This also breaks the loop, but it retrieves the remaining
arguments in the list and pass them as a braced argument
to \arg{code}.

\cslist{
  \pausefor/code/
  }
This interrupts the loop and executes \arg{code}; the loop
being interrupted means you're in the middle of the list, and
you can process it. Such a pause must be terminated by a
\com\resumefor if you don't want nasty internal code
to surface.

\cslist{
  \resumefor\com\dofor
  }
This restarts the current loop. It is necessary to specify
\com\dofor, because \com\resumefor is more general and is
used to restart any kind of loop, especially those defined
with \com\newfor (see next page).

\Example
\dofor{a,b,c,}#1,{[#1]}{}
\Example/

\Example
\dofor{(a=13)(b=3)(c=54)(d=33)(e=22)}(#1=#2){%
  \straighteniff{ifnum}{#2>50 }
    {\breakfor{There's a number larger than 50: #1=#2.}}}
  {No number larger than 50.}
\Example/

\Example
\dofornoempty{dd,e,,acb,3,ee4,,,}#1,{%
  \dofor{#1}##1{[##1]}{}...%
  }{}
\Example/

\vskip\baselineskip

The \com\dofor loop does not perform any kind of normalisation
on the list. I.e. the list must be exactly designed to match
the parameter text, including spaces and other unwelcome guests.

The \com\dofor macro is useful for straightforward loops used once
or twice in a document. But for fully fledged total-control
fully expandable hey-that's-too-cool loops, you should use the
\com\newfor construction.


\description/













\description{For statements: first steps}

\cslist{
  \newfor\comarg\barg{optional passed arguments},
  \zilch\kern-4em/parameter text/\barg{definition}[/optional coda/]
  }
This creates a recursive \comarg\ that will consume all input
with structure \arg{parameter text}. Let's forget
\barg{optional arguments} for a while, since they're optional
(albeit braced). Let's forget the optional coda as well. So
it boils down to:

\vskip\baselineskip
\noindent\com\newfor\comarg\arg{parameter text}\barg{definition}
\vskip\baselineskip

\noindent so that basically \com\newfor works like \com\def.
The \arg{parameter text} is a real parameter
text as with \com\def, just like \barg{definition} is a real
definition, hence the braces. The only difference is there must
be at least one argument,  because we need something to loop
upon. I.e. \arg{parameter text} is at least \verb/#1/.

Now you can launch \comarg\ on an argument which is made of as
many occurrences of \arg{parameter text} as you wish, and on each
occurrence \arg{definition} will be executed. So you've created
a loop. And the good news is that this loop is fully expandable.

It is your job to make sure that what is fed to \comarg\ has
the correct argument structure.

If \arg{coda} is specified, it is executed when the loop ends,
if it ends naturally, i.e. by exhausting its input, and not
by some of the loop-breaking commands on the next page. There
can be no call to arguments of \arg{parameter text} in the 
\arg{coda}, e.g.

\example
\newfor\foo#1{...}[...#1...]
\example/

\noindent is impossible. (You'll get raw inner code.) Such
reference to arguments in the \arg{coda} is possible only
with passed arguments, as you'll see in two pages
from here.

(Note that if there's no \arg{coda}, any space will be gobbled
after \barg{definition}. This is so because I thought it was better
to be able to write \tcode{[\arg{code}]} after a space, e.g.
a line end, than to stick it to \barg{definition}, even though
that brings this little inconvenience, which is probably harmless
since \com\newfor is very unlikely to end up anywhere in horizontal
mode, i.e. in a paragraph.)

Macro thus created can be freely embedded into one another.

\Example
\newfor\foo#1,{(#1)}
\foo{a,b,c,}
\Example/


\cslist{
  \newfornoempty
  }
The \com\newfornoempty is similar to \com\newfor, except \arg{definition}
is not executed in the case the \ital{first} argument is empty.


\Example
\newfornoempty\foo(#1,#2){[#1/#2]}
                         [Input exhausted.]
\edef\bar{\foo{(a,b)(c,d)(,e)(f,)}}
\meaning\bar
\Example/

\Example
\newfor\values#1=#2,{%
  The value of #1 is #2.\par
  }
\def\setvalues#1{%
  \ifsuffix,{#1}{\values{#1}}
                {\values{#1,}}%
  }
\setvalues{A=12,B=45,}
\setvalues{C=34}
\Example/

\Example
\newstring, % \pdfliteral requires full expansion!
\def\drawline#1{
  0 0 m % Initializes the path
  \ifsuffix,{#1}{\drawlinefor{#1}}
                {\drawlinefor{#1,}}
  }                             % l = line
\newfor\drawlinefor#1 #2,{#1 #2 l }[S]% S = draw path
\pdfliteral{
  q  % kind of PDF \bgroup
  1 0 0 RG \drawline{20 10, 40 -15, 100 0,}
  0 1 0 RG \drawline{30 -15, 60 10, 130 0}
  Q} % kind of PDF \egroup
\Example/

\description/








\description{For statements: interruptions}
\advance\vsize by 2\baselineskip

\noindent (The commands on this page are the same as those
introduced with \com\dofor; they're explained
more thoroughly here.)

\cslist{
  !\breakfor/code/
  }
Used inside a loop created with \com\newfor, this
interrupts it, gobbles the remaining input, and 
executes \arg{code}. If the loop had a \arg{coda},
it is not executed. Any material between the \com\breakfor
command and the end of the definition of the loop
is gobbled. It is especially bad with conditionals,
so you should use \com\afterfi, or better yet a
\com\straightenif version.

\Example
\newfor\foo#1{%
  \straighteniff{if}{\noexpand#1z}
    {\breakfor{There is a `z'!}}
    #1... % This will be gobbled.
  }[There is no `z'...]

\foo{abcdef}\par
\foo{abzdef}
\Example/

\cslist{
  !\retrieverest/code/
  }
This does the same thing as \com\breakfor, i.e. breaks the
current loop, but it passes the rest of the material initially
passed to the loop as a braced argument to \arg{code}. Arguments
in that remaining material
aren't extracted from their surrounding delimiters, if any.

\Example
\def\remainder#1{(And `#1' was still to come.)}
\newfor\foo#1=#2,{%
  \unless\ifnum#1=#2 
    \afterfi{% Thrilling...
      \retrieverest{There is a false equation!
                    \remainder}}%
  \fi}
\foo{3=3,2=2,451=451,7=4,78=78,9=0,}
\Example/


\cslist{
  !\pausefor/code/,
  !\resumefor/loop command/
  }
The \com\pausefor command stops the loop and executes \arg{code}.
That means that you're in the middle of the material being processed and
you can act on it. It is useful if the material isn't totally
regular. For instance, a typical Bib\TeX\ entry is a list of
`\tcode{\arg{field}=\arg{value}}' pairs, with each pair
terminated by a comma and the \arg{value} either between braces
or quotes. Thus, you can't have a simple

\example
\newfor\bibfor#1=#2,{#1...#2}
\example/{}{}

\noindent to process the entry, because a \arg{value} may be delimited
by quotes and still contain a comma, and quotes mean nothing to \TeX,
so the comma will be mistaken for the delimiter. An oversimplified
solution with \com\pausefor can be seen on the right. The loop actually
works on the predictable part only (before the equal sign), is interrupted,
the value is retrieved, and the loop is resumed.
(Why one would want to process a Bib\TeX\ entry
with \TeX\ in the first place is a question I can personally answer.)

Once \com\pausefor is used, there must be somewhere down your code
a \com\resumefor\comarg\ statement, to launch the loop again, otherwise
you'll end up stumbling on some nasty internal code. It is impossible
to know (in a perfectly expandable way) the loop we're currently in, hence
the \comarg\ as a argument to \com\resumefor: it is the loop one wants to
start again. Yes, it means you can also process the rest of the material
with another loop, the consequences of which I leave it to you to ponder.
Passed arguments, if any, should follow \comarg\ after \com\resumefor.


\Example
\newfor\bibfor#1={%
  \pausefor{\getvalue{#1}}}
\def\getvalue#1{%
  \trim{#1}:
  \ifnextnospace"{\getquotevalue}
                 {\getcommavalue}
  }
\def\getquotevalue"#1",{\showvalue{#1}}
\def\getcommavalue#1,{\showvalue{#1}}
\def\showvalue#1{%
  {\it\trim{#1}}.\par\resumefor\bibfor}

\bibfor{
  Author = {John Doe},
  Title  = "Me, myself and I",
  Year   = 1978,}
\Example/

\description/







\description{For statements: passed arguments}
\advance\vsize by \baselineskip


Suppose you want to retrieve the largest number in
a list a numbers. The first example on the right shows
you how to do so. But this solution won't work
if you need the loop to be expandable, because there's
a number assignment.

\Example
\newcount\largest
\newfor\findlargest#1,{%
  \ifnum#1>\largest
    \largest=#1
  \fi}
  [The largest number is \the\largest.]

\findlargest{45,33,1,4844,12,655,}
\Example/

That's why loops defined with \com\newfor can pass
arguments from one iteration to the next. The number of those arguments
are the \barg{optional passed arguments} in the description
of \com\newfor two pages ago. So, a typical fully-fledged
use of \com\newfor is:

\example
\newfor\myloop{2}#3=#4,{...#1...#2...#3...#4...}
                       [...#1...#2...]
\example/

\noindent which means that \com\myloop takes four arguments,
two of which are actually passed arguments, the third and the
four being in the recursive list that \com\myloop runs on.
Besides, as you can see, passed arguments can appear in
\arg{coda}.
Now a call to \com\myloop looks like:

\example
\myloop{one}{two}{a=1,b=2,...}
\example/

\noindent where \tcode{one} and \tcode{two} are passed
arguments. There can be up to 8 passed arguments (since there must
be at least one argument to loop on), and if there are
{\it n} of them, numbering of arguments in \arg{parameter text} must
start at {\it n}+1, as in the above example.


\cslist{
  \passarguments/arg1//arg2/...
  }
Passed arguments are automatically retrieved from one iteration
to the next. However, if you can't change them, they aren't very
interesting. Hence this command: it passes \arg{arg1}, \arg{arg2}, etc.,
to the next iteration, replacing the previous ones. There
must be as many arguments to \com\passarguments as required
by the loop, even if you don't want to pass new values for
all (in which case, just pass the previous value).
Beware: \com\passarguments ends the current iteration, just
like \com\breakfor,
and any remaining material in the definition of the loop
is gobbled.

Thus, the second version of our \com\findlargest command
works as follows: it takes one harmless passed argument,
and loops on the following list. Obviously, 45 is larger
than 0, so it is passed as the new first argument; then,
33 is not larger than 45, so nothing happen, and 45 is
implicitly passed again as the first argument, and so
on and so forth, until finally the \arg{coda} prints
the largest number in the list. And, as illustrated
by the \com\edef, everything expands nicely.

\Example
\newfor\findlargest{1}#2,{%
  \straighteniff{ifnum}{#2>#1 }
                {\passarguments{#2}}%
  }
  [The largest number is #1.]

\edef\foo{\findlargest{0}{45,33,1,4844,12,655,}}
\meaning\foo
\Example/

\description/








\description{For statements: examples}


Loops created with \com\newfor are somewhat tricky
to get a hand on, so here are some examples. First
of all, you might think that it would be nice to
be able to define a loop whose argument structure
is defined but not its replacement text, so that you
can call it on similar lists but with different
operations. For instance, a generic loop that works
on all comma-separated lists. You can't do that exactly
with \com\newfor, but you can easily use passed arguments
to do something similar, e.g.:

\example
\newfor\commalist{1}#2,{#1{#2}}
\commalist\tree{leaf,fruit,twig,}
\commalist\scale{b minor,f sharp,whatever lydian}
\example/

\noindent with \com\tree and \com\scale defined to
process one argument: \com\commalist itself has no real
definition, and you don't have to bother about passed
arguments (although you can still use them).

\Example
\newfor\sortnum{1}#2,{%
  \subsortnum{#2}{}{#1}%
  }[Sorted list: #1]
\newfor\subsortnum{2}#3,{%
  \straightenif{ifnum}{#1<#3 }
         {\retrieverest{\passtosortnum{#2#1,#3,}}}
         {\passarguments{#1}{#2#3,}}%
  }[\passarguments{#2#1,}]
\def\passtosortnum#1#2{\passarguments{#1#2}}

\sortnum{}{5,12,-161,3,0,63,22,-45,}
\Example/

The first example sorts a list of numbers separated
by commas. The first loop, \com\sortnum, takes a passed
argument which contains the numbers already sorted (so
it is empty at the beginning) and it runs on the list
to be sorted. The second loop, \com\subsortnum, takes
two passed arguments: the first one is the number under
investigation, the second one is the list of numbers
smaller than the number under investigation (so it is
empty too at the beginning), and it is updated each
time we find such a number as the third, non-passed
arguments to \com\subsortnum, which is an element of
the list of already sorted numbers as preserved in
\com\sortnum's first passed argument... got that?

Let's follow some iterations. The first call is:

\example
            % incoming arguments 
\sortnum{}5,12,-161,3,0,63,22,-45,
\example/

\noindent and it calls

\example
\subsortnum{5}{}{}
\example/

\noindent so that \com\subsortnum terminates immediately:
it has no input. So it calls its coda:

\example
\passarguments{5,}
\example/

\noindent (where \tcode{5} is really the first argument following
the empty second one). Since \com\subsortnum has terminated, this
call to \com\passarguments is for \com\sortnum, hence the following
iteration is:

\example
              % incoming arguments
\sortnum{5,}12,-161,3,0,63,22,-45,
--> \subsortnum{12}{}5,
\example/

\noindent Ah, something new. 12 is larger than 5, so the conditional
is false. So \com\subsortnum passes the following to itself:

\example
\passarguments{12}{5,}
--> \subsortnum{12}{5,}{}
\example/

\noindent and once again it terminates, hence:

\example
\passarguments{5,12,}   % incoming arguments
--> \sortnum{5,12,}-161,3,0,63,22,-45,
                         % incoming argument
--> \subsortnum{-161}{}5,12,
\example/

\noindent and obviously -161 is smaller than 5, so the rest of the list
is retrieved with \com\retrieverest and passed as the second argument of
\com\passtosortnum. Once again, since this terminates \com\subsortnum,
\com\passarguments in \com\passtosortnum is for \com\sortnum:

\example
\passtosortnum{-161,5,}{12,}
                          % incoming arguments
--> \sortnum{-161,5,12,}3,0,63,22,-45,
                         % incoming arguments
--> \subsortnum{3}{}-161,5,12,
--> \subsortnum{3}{-161,}5,12,
--> \passarguments{161,3,5,12,}
--> \sortnum{-161,3,5,12,}0,63,22,-45,
...
\example/


\noindent and so on and so forth.

Replace the test with any other one and you
have a generic sorting function, as in the example
on the right, which sorts entries alphabetically
or chronologically. It is possible to make things both 
cleverer and simpler. (The Lua code compares two
strings, and it could very well have handled the
\com\year version.)

\Example
\newfor\sortbooks{2}#3(#4),{%
  \subsortbooks#1{#3(#4)}{}{#2}
  }[\bgroup\it#2\egroup]
\newfor\subsortbooks{3}#4(#5),{%
  #1#2{#4}{#5}{#3}
  }[\passarguments#1{#3#2,}]

\def\alpha#1(#2)#3#4#5{%
  \directlua{
    if "#1"<"#3" then 
      tex.print("\noexpand\\firstoftwo")
    else 
      tex.print("\noexpand\\secondoftwo")
    end}
    {\retrieverest{%
      \passtosortbooks\alpha{#5#1(#2),#3(#4),}}}
    {\passarguments\alpha{#1(#2)}{#5#3(#4),}}
  }
\def\year#1(#2)#3#4#5{
  \straightenif{ifnum}{#2<#4 }
      {\retrieverest{%
        \passtosortbooks\year{#5#1(#2),#3(#4),}}}
      {\passarguments\year{#1(#2)}{#5#3(#4),}}
  }
\def\passtosortbooks#1#2#3{\passarguments#1{#2#3}}

\def\books{
  Oblivion (2004),
  Infinite Jest (1996),
  Brief Interviews with Hideous Men (1999),
  Girl with Curious Hair (1989),
  The Broom of the System (1987),
  The Pale King (2011),% No parasitic space!
  }
David Foster Wallace's books in alphabetical order:\par
\passexpanded{\sortbooks\alpha{}}\books \par
David Foster Wallace's books ordered by date:\par
\passexpanded{\sortbooks\year{}}\books 
\Example/

\vskip\baselineskip

The next example is a palindrome detector: it returns
true if the string it is fed is made of a string followed
by itself reverse (which is not the exact definition of
a palindrome, which is a string that is its own reverse,
but we keep things simple).

The first loop, \com\palincount, simply counts the number
of characters in the string; it also reaccumulates it
as its second argument, something that could be avoided
if there was a wrapper macro. Once it is finished, it
passes the original string along with half the number
of characters to \com\palincheck, which simply accumulates
in reverse this number of characters, by decreasing it
on each iteration. Once this number is exhausted, it
compares what it has accumulated to what there remains
to be processed, and if both strings match, the original
string is a palindrome.

\Example
\newfor\palincount{2}#3{%
  \passarguments{\numexpr(#1+1)}{#2#3}%
  }[\palincheck{\numexpr(#1/2)}{}{#2}]
\newfor\palincheck{2}#3{%
  \reverse\straightenif{ifnum}{\numexpr(#1-1)>0 }
               {\retrieverest{\compare{#3#2}}}
               {\passarguments{\numexpr(#1-1)}{#3#2}}%
  }
\def\compare#1#2{%
  \ifstring{#1}{#2}{TRUE}{FALSE}%
  }

\edef\foo{\palincount{0}{}{abcdeffedcba}}
\edef\bar{\palincount{0}{}{abcdff}}
\meaning\foo, \meaning\bar
\Example/


\description/


\bye