%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% Module: ZZTeX Programming Constructs
%
% Synopsis: This module contains definitions for ZZTeX's programming
% constructs. These constructs provide various extensions
% to TeX's sometimes meager repertoire of programming
% features.
%
% Author: Paul C. Anagnostopoulos
% Created: 27 March 1989
%
% Copyright 1989--2020 by Paul C. Anagnostopoulos
% under The MIT License (opensource.org/licenses/MIT)
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Token Hackery
% ----- -------
% We need a name for a space token.
\def \\{\let \zspacetoken = } \\ % Now \zspacetoken is a space token.
% This macro discards the next token.
\def \discardtok #1{}% token
% This macro removes the `pt' following a dimension.
{\catcode `\p = \catother \catcode `\t = \catother
\gdef \zremovedu #1pt{#1}
} % \catcode
% Using that macro, we can define a macro that "converts" a dimen register
% into a factor.
\def \thefactor #1{\expandafter\zremovedu \the#1}
% This macro extracts the contents of a macro and returns it as plain text.
% Usage: \expandafter\zdefof \meaning\macro\zmark
\def \zdefof #1:->#2\zmark{#2}
% Control Sequence Names
% ------- -------- -----
\def \name #1{% {\tokens}
\csname \expandafter\discardtok \string#1\endcsname}
\def \withname #1#2{% {\command}{\tokens}
\expandafter#1\csname \expandafter\discardtok \string#2\endcsname}
% Macro Expansion
% ----- ---------
\def \expandaftertwice {\expandafter\expandafter\expandafter}
\def \expandafterthrice {\expandafter\expandafter\expandafter\expandafter
\expandafter\expandafter\expandafter}
\def \zoneoftwo #1#2{#1}% {first}{second}
\def \ztwooftwo #1#2{#2}% {first}{second}
\def \zoneofthree #1#2#3{#1}% {first}{second}{third}
\def \ztwoofthree #1#2#3{#2}% {first}{second}{third}
\def \zthreeofthree #1#2#3{#3}% {first}{second}{third}
\def \zoneoffour #1#2#3#4{#1}% {first}{second}{third}{fourth}
\def \ztwooffour #1#2#3#4{#2}% {first}{second}{third}{fourth}
\def \zthreeoffour #1#2#3#4{#3}% {first}{second}{third}{fourth}
\def \zfouroffour #1#2#3#4{#4}% {first}{second}{third}{fourth}
% Flags (Booleans)
% ----- ----------
% The boolean literals \true and \false are appropriate for use with
% the \if command, which tests the codes of the next two characters.
\def \true {TT}
\def \false {FL}
\def \setflag #1=#2{\edef #1{#2}}% \flag = boolean
% IF and Predicates
% -- --- ----------
% A "predicate" is a macro that returns \true or \false as its value.
% Such values are suitable for use with the \if conditional. For example:
%
% \if \oddp{\x} <then-clause> \else <else-clause> \fi
% A predicate can be used with \setflag as follows:
%
% \setflag \flag = {<predicate>}
% Here are the predicates for TeX's repertoire of conditional
% commands. These might be more appropriately interspersed with
% other definitions in this module, but what the heck.
% Some additional "obvious" predicates are defined.
\def \eqlp #1#2{\ifnum #1 = #2\true \else \false \fi}
\def \neqlp #1#2{\ifnum #1 = #2\false \else \true \fi}
\def \lssp #1#2{\ifnum #1 < #2\true \else \false \fi}
\def \gtrp #1#2{\ifnum #1 > #2\true \else \false \fi}
\def \zerop #1{\ifnum #1 = 0\true \else \false \fi}
\def \onep #1{\ifnum #1 = 1\true \else \false \fi}
\def \posp #1{\ifnum #1 > 0\true \else \false \fi}
\def \negp #1{\ifnum #1 < 0\true \else \false \fi}
\def \oddp #1{\ifodd #1\true \else \false \fi}
\def \evenp #1{\ifodd #1\false \else \true \fi}
\def \rangep #1#2#3{\if \orp{\lssp{#1}{#2}}{\gtrp{#1}{#3}}\false \else
\true \fi}
\def \tensp #1{\rangep{#1}{10}{19}}
\def \dimeqlp #1#2{\ifdim #1 = #2\true \else \false \fi}
\def \dimneqlp #1#2{\ifdim #1 = #2\false \else \true \fi}
\def \dimlssp #1#2{\ifdim #1 < #2\true \else \false \fi}
\def \dimgtrp #1#2{\ifdim #1 > #2\true \else \false \fi}
\def \dimzerop #1{\ifdim #1 = 0pt\true \else \false \fi}
\def \dimposp #1{\ifdim #1 > 0pt\true \else \false \fi}
\def \dimnegp #1{\ifdim #1 < 0pt\true \else \false \fi}
\def \vmodep {\ifvmode \true \else \false \fi}
\def \hmodep {\ifhmode \true \else \false \fi}
\def \mathmodep {\ifmmode \true \else \false \fi}
\def \textmodep {\ifmmode \false \else \true \fi}
\def \innermodep {\ifinner \true \else \false \fi}
\long\def \codeeqlp #1#2{\if #1#2\true \else \false \fi}
\long\def \cateqlp #1#2{\ifcat #1#2\true \else \false \fi}
\long\def \tokeqlp #1#2{\ifx #1#2\true \else \false \fi}
\long\def \xtokeqlp #1#2{\expandafter\ifx #1#2\true \else \false \fi}
\long\def \definedp #1{%
\expandafter\ifx \csname \expandafter\discardtok \string#1\endcsname
\relax \false \else \true \fi}
\long\def \undefinedp #1{%
\expandafter\ifx \csname \expandafter\discardtok \string#1\endcsname
\relax \true \else \false \fi}
\def \zempty {}
\def \emptydefp #1{\ifx #1\zempty \true \else \false \fi}% {\name}
\let \emptylistp = \emptydefp
\long\def \emptyargp #1{% {#n}
\zempargp #1\zempargq\zmark}
\long\def \zempargp #1#2\zmark{%
\ifx #1\zempargq \true \else \false \fi}
\def \zempargq {\zempargq}
\def \emptytoksp #1{% {\tokenreg}
\expandafter\zemptoksp \the#1\zmark}
\long\def \zemptoksp #1\zmark{\emptyargp{#1}}
\def \voidboxp #1{\ifvoid #1\true \else \false \fi}
\def \hboxp #1{\ifhbox #1\true \else \false \fi}
\def \vboxp #1{\ifvbox #1\true \else \false \fi}
\def \eofp #1{\ifeof #1\true \else \false \fi}
% Flags can also be used as predicates, as in:
%
% \if \flaga <then-clause> \else <else-clause> \fi
% Now here we have predicates for the common logical operators.
\def \notp #1{\if #1\false \else \true \fi}
\def \andp #1#2{\if #1#2\else \false \fi}% {boolean1}{boolean2}
\def \orp #1#2{\if #1\true \else #2\fi}% {boolean1}{boolean2}
% Pseudo-Predicates
% -----------------
\def \stringeql #1#2#3{% {\return-flag}{string1}{string2}
\edef \zstra {#2}%
\edef \zstrb {#3}%
\edef #1{\ifx \zstra\zstrb \true \else \false \fi}}
\def \gluevaries #1#2{% {\return-flag}{glue}
\zskipa = #2\relax
\tdimena = \zskipa
\stringeql{#1}{\the\zskipa}{\the\tdimena}%
\edef #1{\if #1\false \else \true \fi}}
% Arithmetic
% ----------
\def \negate #1{\multiply #1 by -1\relax}% {\register}
\def \increment #1{\advance #1 by 1\relax}% {\count}
\def \decrement #1{\advance #1 by -1\relax}% {\count}
% Looping
% -------
\def \loop #1\repeat{% body [actions] \if condition [actions] \repeat
\def \zloopbody {#1}%
\zloop}
\def \zloop {%
\zloopbody
%\if condition
\let \zloopnext = \zloop
\else
\let \zloopnext = \relax
\fi
\zloopnext}
\let \repeat = \fi