% \iffalse meta-comment
%
% Copyright 1994 the LaTeX3 project and the individual authors.
% All rights reserved. For further copyright information see the file
% legal.txt, and any other copyright indicated in this file.
% 
% This file is part of the LaTeX2e system.
% ----------------------------------------
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%  This system is distributed in the hope that it will be useful,
%  but WITHOUT ANY WARRANTY; without even the implied warranty of
%  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
% 
% 
% IMPORTANT NOTICE:
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% \fi
% \iffalse
%%
%% File `ifthen.dtx'.
%% Copyright (C) 1991 by Leslie Lamport
%% Copyright (C) 1994, 1994 LaTeX3 project, David Carlisle
%%                       all rights reserved.
%%
%
%<package>\NeedsTeXFormat{LaTeX2e}[1994/05/22]
%<package>\ProvidesPackage{ifthen}
%<package>        [1994/05/27 v1.0i Standard LaTeX ifthen package (DPC)]
%
%<*driver>
\documentclass{ltxdoc}
\usepackage{ifthen}
\GetFileInfo{ifthen.sty}
\begin{document}
\title{The \textsf{ifthen} package\thanks{This file
        has version number \fileversion, last
        revised \filedate.}}
\author{David Carlisle}
\date{\filedate}
\author{David Carlisle}
 \maketitle
 \DocInput{ifthen.dtx}
\end{document}
%</driver>
% \fi
%
% \CheckSum{267}
%
%
% \begin{abstract}
% This file implements an |\ifthenelse| command for \LaTeXe.
% The algorithm used is compatible with that used in the \LaTeX~2.09
% |ifthen| style option. It has been recoded, making the resulting
% definitions somewhat more compact and efficient.
% \end{abstract}
%
% \changes{v1.0a}{1993/10/15}{New implementation}
% \changes{v1.0b}{1993/12/17}{Upgrade to LaTeX2e}
% \changes{v1.0e}{1994/02/11}{Improve documentation}
% \changes{v1.0f}{1994/03/02}{Remove need for dtx file}
% \changes{v1.0g}{1994/03/14}{Modify for the new ltxdoc.cls}
%
% \section{Introduction}
%
% \DescribeMacro{\ifthenelse}
% |\ifthenelse{|^^A
%       \meta{test}|}{|\meta{then clause}|}{|\meta{else clause}|}|
%
% Evaluates \meta{test} as a boolean function, and then executes
% either \meta{then clause} or \meta{else clause}.
%
% \meta{test} is a boolean expression using the infix connectives,
% |\and|, |\or|, the unary |\not| and parentheses |\( \)|.
%
% The atomic  propositions are:\\
% \meta{number} |<| \meta{number} \\
% \meta{number} |=| \meta{number} \\
% \meta{number} |>| \meta{number} \\
% |\isodd{| \meta{number} |}|\\
% |\equal{|\meta{string}|}{|\meta{string}|}|\\
% |\lengthtest{|\meta{dimen}|<|\meta{dimen}|}|\\
% |\lengthtest{|\meta{dimen}|=|\meta{dimen}|}|\\
% |\lengthtest{|\meta{dimen}|>|\meta{dimen}|}|\\
% |\boolean{|\meta{name}|}|
%
% The \meta{string}s tested by |\equal| may be any sequence of commands
% that expand to a list of tokens. If these expansions are equal, then
% the proposition is true.
%
% |\isodd| is true if the \meta{number} is odd, and false otherwise
% (even if the argument is not a number).
%
% |\boolean{xyz}| returns the truth value contained in the primitive
% \TeX\ |\if|, |\ifxyz|. This is usually used with |\newif| created
% tokens, but can also be used with |\boolean{true}| (|\iftrue|),
% |\boolean{mmode}| (|\ifmmode|) etc.
%
% \DescribeMacro{\newboolean}
%  The commands:\\
%  |\newboolean{|\meta{name}|}| and\DescribeMacro{\setboolean}
%  |\setboolean{|\meta{name}|}{|\meta{value}|}|\\
% are provided so the user can easily create and set these flags.
% \meta{value} may be either |true| or |false| (any CaSe).
%
% Note that there is no precedence between |\and| and |\or|.
% The proposition is evaluated in a left right manner. |\not| only
% applies to the immediately following proposition. (This is consistent
% with Lamport's |ifthen.sty|. In this style, though the test is
% `lazily' evaluated, so for instance if the first proposition in an
% |\or| is true, the second one is skipped. (On the second pass---The
% first pass in an |\edef| expands clauses in all propositions).
%
% Apart from the addition of the extra atomic propositions |\isodd|,
% |\boolean| and |\lengthtest|, the only known incompatibility is that
% in this package the expression|\not\not|\meta{P} is equivalent to
% \meta{P}.
% However in the original style it was equivalent to |\not|\meta{P}.
% This is intentional (bug fix:-).
%
% \DescribeMacro{\whiledo}
% The command |\whiledo| is also defined (copied directly from
% The \LaTeX2.09 definition).
%
% |\whiledo{|\meta{test}|}{|\meta{while clause}|}|
%
% With \meta{test} as above, repeatedly executes \meta{while clause}
% while the test remains true.
%
% \StopEventually{}
%
% \section{The Implementation}
%
%    \begin{macrocode}
%<*package>
%    \end{macrocode}
%
% \begin{macro}{\TE@throw}
% In order to support the syntax of |ifthen.sty|, which allows access
% to the primitive \TeX\ syntax for a numeric test, rather than a |{}|
% delimited argument form, it is most convenient to work `within' an
% |\ifnum|. |\ift@throw| `throws' you out of the current |\ifnum| so
% that you can (eg) start an |\ifdim| for the length tests.
%    \begin{macrocode}
\def\TE@throw{\@ne=\@ne\noexpand\fi}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\boolean}
% A non-standard extension to |ifthen|, supporting boolean was
% previously available, this is a simpler implementation.
%    \begin{macrocode}
\def\boolean#1#2{%
  \TE@throw\expandafter\noexpand\csname if#1\endcsname#2}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\TE@length}
% Testing lengths. |#1| is the test. The extra argument gobbles spaces.
%    \begin{macrocode}
\def\TE@length#1#2{\TE@throw\noexpand\ifdim#1#2}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\TE@odd}
% \begin{macro}{\TE@@odd}
% Testing odd/even. This is true if |#1| is an odd number, and false
% otherwise (even if |#1| is not a number at all).
%
% It is hard to make this completely reliable. Here I have erred on the
% side of safety. This should not generate a \TeX\ error if given any
% robust commands as its argument. However it returns true on any
% argument that \emph{starts} with an odd number |11xx| which is bad,
% and it can not deal with \TeX's count registers, although \LaTeX\
% counters work (via |\value|).
% \changes{v1.0b}{1993/12/17}{Improve \cmd\isodd}
% \changes{v1.0c}{1994/01/20}{Improve \cmd\isodd\ again}
%    \begin{macrocode}
\def\TE@odd#1#2{%
  \TE@throw\noexpand\TE@@odd#1\noexpand\@nil\noexpand\ifodd\count@#2}
%    \end{macrocode}
%
% |\TE@@odd| is not expanded on the first pass.
%    \begin{macrocode}
\def\TE@@odd#1#2\@nil{%
  \@defaultunits
  \count@\if-#1-0\else0\expandafter#1\fi#2\relax\@nnil}
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
%  \begin{macro}{\TE@repl}
% |\TE@repl| replaces the single token |#1| by |#2|. (Not within |{}|
% groups.) It is used to replace |\or| by |\TE@or| without the need to
% redefine |\or|. Earlier versions just |\let\or\TE@or| but this has a
% bad effect on the expansion of commands which use the primitive
% |\or| internally, eg |\alph|, and so caused surprising results if
% these commands were used inside |\equal|.
% \changes{v1.0h}{1994/05/14}{macro added}
%    \begin{macrocode}
\def\TE@repl#1#2{%
  \long\def\@tempc##1#1##2{%
    \def\@tempa{##2}\def\@tempb{\@tempc}%
    \ifx\@tempa\@tempb
     \toks@\expandafter{\the\toks@##1}%
     \expandafter\@gobble
    \else
      \toks@\expandafter{\the\toks@##1#2}%
    \expandafter\@tempc
    \fi
    ##2}%
  \expandafter\toks@\expandafter{\expandafter}%
  \expandafter\@tempc\the\toks@#1\@tempc}
%    \end{macrocode}
%  \end{macro}
%
%
% \begin{macro}{\ifthenelse}
% The remaining macros in this file are derived from the ones in
% |ifthen.sty| but recoded and simplified. The main simplification is
% that the original style (and the |\boolean| extensions) expressed
% logical values always in terms of |\ifnum|. As |\fi| is `untyped' this
% is not necessary, so for example the length tests can return values
% via |\ifdim|, the trailing |\fi| will not complain, even though it was
% `expecting' an |\ifnum|. Also the system of passing information via
% macros expanding to |T| or |F| has been completely replaced by a
% simpler system using |\iftrue|, which furthermore allows lazy
% evaluation on the second pass.
%    \begin{macrocode}
\long\def\ifthenelse#1{%
%    \end{macrocode}
% \changes{v1.0h}{1994/05/14}{Use \cs{TE@repl}}
%    \begin{macrocode}
\toks@{#1}%
\TE@repl\or\TE@or
\TE@repl\and\TE@and
\TE@repl\not\TE@neg
%    \end{macrocode}
% The original |ifthen.sty| processed everything inside a box
% assignment, to catch any extra spaces before they appeared in the
% output. Instead I have added extra arguments to the commands so they
% each remove any following space.
%
% Set up the user level names |\not| etc.
% \changes{v1.0c}{1994/01/20}{Modify\cmd\protect\ and \cmd\value}
%    \begin{macrocode}
    \bgroup
        \def\protect{\noexpand\protect\noexpand}%
        \def\value##1{\the\csname c@##1\endcsname}%
        \let\equal\TE@equal \let\(\TE@lparen \let\)\TE@rparen
        \let\isodd\TE@odd \let\lengthtest\TE@length
%    \end{macrocode}
% For the first pass, in a group, make various tokens non-expandable.
%
% It is unfortunate that in order to remain compatible with |ifthen|
% syntax, it is necessary to have a two pass system. The first pass
% inside an |\edef| `exposes' the |\if|\ldots\ |\fi| tokens, so the
% corect clauses may be skipped on the second pass. This means that the
% whole |\ifthenelse| command does not work by expansion, and so
% possibly has only limited usefulness for macro code writers.
% The main problem with the |ifthen:| syntax is that (unique for \LaTeX)
% it does not uses a brace delimited argument form, and exposes the
% primitive \TeX\ syntax for \meta{number}. Pretty much the only way of
% parsing |1 > 2 \or 2 < 1| is to actually evaluate the primitive
% |\ifnum|s. A syntax such as:\\%
% |\or{\numtest{1<2}}{\lengthtest{1pt<1in}}|\\
%  could easily be evaluated in a one pass way, operating directly via
%  expansion, and leaving no extra tokens in the token stream.
%
% Still, on with the code\ldots\ make |\@tempa| and |\@tempb| tokens
% non-expandable on the first pass.
%    \begin{macrocode}
        {\let\@tempa\relax\let\@tempb\relax
        \xdef\@gtempa{\expandafter\TE@eval\the\toks@\TE@endeval}}%
%    \end{macrocode}
% Now outside the group, execute |\@gtempa| which causes all the
% |\if|s etc., to be evaluated, the final truth value is contained in
% the |\newif| token |\ifTE@val|. Finally this is tested and either the
% first or second following argument is chosen accordingly.
% \changes{v1.0d}{1994/01/24}
%     {Use \cmd{\@firstoftwo} not \cmd{\@leftmark}}
%    \begin{macrocode}
        \@gtempa
        \expandafter\egroup\ifTE@val
          \expandafter\@firstoftwo
        \else
          \expandafter\@secondoftwo
        \fi}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\TE@eval}
% Initialise a term. (Expanded on the first pass).
%    \begin{macrocode}
\def\TE@eval{\noexpand\TE@negatefalse\noexpand\iftrue\noexpand\ifnum}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\ifTE@val}
% \begin{macro}{\ifTE@negate}
% Two |\newif|s the first holds the current truth value of the
% expression. The second is a temporary flag which is true if we need to
% negate the current proposition.
%    \begin{macrocode}
\newif\ifTE@val
\newif\ifTE@negate
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\TE@endeval}
% Finalise a term. (Expanded on the first pass).
%    \begin{macrocode}
\def\TE@endeval{\relax
      \noexpand\TE@setvaltrue\noexpand
    \else
      \noexpand\TE@setvalfalse\noexpand
    \fi
    \noexpand\TE@negatefalse\noexpand
  \fi}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\TE@setvaltrue}
% \begin{macro}{\TE@setvalfalse}
% Set the |\ifTE@val| to true or false depending on the value of the
% current proposition, and the negate flag. (Not expanded on the first
% pass.)
%    \begin{macrocode}
\def\TE@setvaltrue{%
  \ifTE@negate\TE@valfalse\else\TE@valtrue\fi}
\def\TE@setvalfalse{\let\ifTE@val\ifTE@negate}
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\TE@or}
% The internal version of |\or|. Ends the current term.
% If true skip the remaining terms.
%    \begin{macrocode}
\def\TE@or{\TE@endeval\noexpand\ifTE@val\noexpand\else\noexpand\ifnum}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\TE@and}
% The internal version of |\and|. If false skip the remaining terms.
%    \begin{macrocode}
\def\TE@and{\TE@endeval\noexpand\ifTE@val\noexpand\ifnum}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\TE@neg}
% \begin{macro}{\TE@negswitch}
% |\not|. Throw the current context, set a negate flag, then restart
% the |\ifnum|. |\TE@negswitch| is not expanded on the first pass.
%    \begin{macrocode}
\def\TE@neg{\TE@throw\noexpand\TE@negswitch\noexpand\ifnum}
\def\TE@negswitch{\ifTE@negate\TE@negatefalse\else\TE@negatetrue\fi}
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\TE@lparen}
% |\(|. Throw the current context, then restart a term inside a group.
%    \begin{macrocode}
\def\TE@lparen#1{\TE@throw\begingroup\TE@eval#1}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\TE@rparen}
% |\)| end the current term, and the local group started by |\(|, but
% pass on the boolean value in |\if\@val T|. The |\noexpand| stops the
% |\expandafter| from expanding on the first pass.
%    \begin{macrocode}
\def\TE@rparen#1{%
  \TE@endeval
  \noexpand\expandafter\endgroup\noexpand\ifTE@val#1}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\TE@equal}
% |\equal| greatly simplified from the original. |\def| may be used
% rather than |\edef| as the whole thing is expanded anyway in the
% first pass. The boolean can be directly encoded with the |\ifx|,
% there is no need to start an equivalent |\ifnum|.
% \changes{v1.0h}{1994/05/14}{make long}
%    \begin{macrocode}
\long\def\TE@equal#1#2#3{\TE@throw
      \def\@tempa{#1}\def\@tempb{#2}%
      \noexpand\ifx\@tempa\@tempb#3}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\boolean}
% |\setboolean| takes |true| or |false|, as |#2|, and sets |#1|
% accordingly.
% \changes{v1.0i}{1994/05/27}{New style error commands}
%    \begin{macrocode}
\def\setboolean#1#2{%
  \lowercase{\def\@tempa{#2}}%
  \@ifundefined{@tempswa\@tempa}%
    {\PackageError{ifthen}%
       {You can only set a boolean to `true' or `false'}\@ehc}%
    {\@ifundefined{#1\@tempa}%
      {\PackageError{ifthen}{Boolean #1 undefined}\@ehc}%
      {\csname#1\@tempa\endcsname}}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\newboolean}
% Oh I do love those |\outer| macros.
%    \begin{macrocode}
\def\newboolean#1{%
  \csname newif\expandafter\endcsname\csname if#1\endcsname}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\whiledo}
% |\whiledo| copied directly from the original.\\
% |\whiledo{|\meta{test}|}{|\meta{body}|}|\\
% repeatedly evaluates \meta{body} until \meta{test} is true.
%    \begin{macrocode}
\long\def\whiledo#1#2{%
  \ifthenelse{#1}{\@whiledotrue \@whilesw\if@whiledo\fi
     {#2\ifthenelse{#1}{\@whiledotrue}{\@whiledofalse}}}{}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\if@whiledo}
% Internal switch for |\whiledo|.
%    \begin{macrocode}
\newif\if@whiledo
%    \end{macrocode}
% \end{macro}
%
%    \begin{macrocode}
%</package>
%    \end{macrocode}
%
% \Finale
\endinput
