I created a small package to help me typeset various tidbits in papers for a specific domain of theoretical computer science that I sometimes work in. So far, it has been working well, but I decided that I wanted to introduce auto-growing brackets since I can sometimes end up with a whole bunch of nested brackets being displayed. To do this, I introduced use of the 'perfectcut' package. Or tried to.
For full reference, you can find the pre-perfectcut implementation here, and the attempt at a new implementation here. The only substantive difference between the two is changing the definitions of cpfunc, cpsend and cprecv, and introducing the new cpsystems@functorparens and cpsystems@msgbraces commands to back said new definitions.
The problem is, with just these changes (and, best as I can tell, the modification to cpfunc was the only one that actually caused these problems), is that now when I try to re-compile my .dtx file (using the command pdflatex cpsystems.dtx), I get a whole bunch of "Misplaced \cr" and "Misplaced alignment tab &" errors. E.g., the very first ones look like:
! Misplaced \cr.
\reserved@c ->\ifnum 0=`{}\fi \cr
l.310 ...func{p}{h(R) \cpfunc{p}{h(F)p(P)}}}~c(W)}
?
! Misplaced alignment tab character &.
<recently read> &
l.310 ...func{p}{h(R) \cpfunc{p}{h(F)p(P)}}}~c(W)}
In the full-blown file, these such errors start at line 310, with more being reported at lines 315, 370 and 375 (though the latter two are actually a repeat of the earlier two, for documentation reasons). Going by discussions of these errors that I could turn up, such as this TeXOverflow question, or this Overleaf help page, I surmise that the errors are probably not occurring there, but likely on the line above. Either way, though, I can't work out what the issue really is.
The lines in question are using a package command, which in turn uses an array environment, to present something. On the previous line, I have included a line break. I have checked, and am fairly certain I have specified the correct number of & characters on those lines to get everything to fit together, and I didn't see any errors previously.
I have done my best to create an example that reproduces the errors, which is below, though it is still awfully long (I wasn't sure what else I could remove without mucking something up):
% \iffalse meta-comment
% !TEX program = pdfLaTeX
%
% \fi
% \iffalse
%<*readme>
%%cpsystems LaTeX package
%</readme>
% \fi
%
% \iffalse
%<*driver>
\ProvidesFile{cpsystems.dtx}
%</driver>
%<package>\NeedsTeXFormat{LaTeX2e}
%<package>\ProvidesPackage{cpsystems}
%<*package>
[2020/07/16 v0.14 Package to aid in typesetting cP systems
rulesets, following Nicolescu's standard style]
%</package>
%
%<*driver>
\documentclass{ltxdoc}
\usepackage{cpsystems}[2020/07/16 v0.14]
\usepackage{fancyvrb}
\usepackage[hidelinks]{hyperref}
\EnableCrossrefs
\CodelineIndex
\RecordChanges
%\OnlyDescription %Leave this commented out unless you have read the Doc documentation and know what you're doing
\begin{document}
\DocInput{cpsystems-autogrow-bracks-mwe.dtx}
\PrintIndex
\PrintChanges
\end{document}
%</driver>
% \fi
%
% \begin{cpruleset}
% \cprule{s_1}{\cpfunc{v}{v(R)Y}}{1}{s_2}{\cpfunc{s}{r(R)~u(Y)~
% \cpfunc{p}{h(R)p()}}~c(\lambda)}
%
% \cprule{s_2}{\cpfunc{s}{r(R)~u() \\ & \cpfunc{p}{h(F)p(P)} \\ & c(C)}}
% {+}{s_3}{\cpfunc{z}{\cpfunc{p}{h(R) \cpfunc{p}{h(F)p(P)}}}~c(W)}
%
% \cprule{s_2}{}{+}{s_2}{\cpfunc{s}{r(R)~u(Z) \\
% & & & & \cpfunc{p}{h(T) \cpfunc{p}{h(F) p(P)}}
% \\ & & & & c(CW)}}
%
% \cprule{s_2}{s(\_)}{+}{s_2}{}
%
% \cprule{s_3}{}{1}{s_4}{p'(P) \quad c'(1D)}
% \end{cpruleset}
% \StopEventually{\PrintIndex}
% \iffalse
%<*package>
% \fi
%
% \iffalse
%
% \fi
%
% \subsection{Preamble}
%
% \begin{macrocode}
%
\RequirePackage{array}
\RequirePackage{framed}
\RequirePackage{changepage}
\RequirePackage{amsmath}
\RequirePackage{trimspaces}
\RequirePackage{newfloat}
\RequirePackage{perfectcut}
\newcounter{cpsystems@RuleNum}
%
% \begin{macrocode}
\newenvironment{cpruleset}
{\begin{framed}\begin{adjustwidth}{-1.0em}{-1.0em}
\renewcommand{\arraystretch}{1.0}\[\begin{array}{lllllr}}
{\end{array}\]\end{adjustwidth}\end{framed}}
% \end{macrocode}
%
% % \begin{macro}{\cprule}
% \begin{macrocode}
\newcommand{\cprule}[5]{
\refstepcounter{cpsystems@RuleNum}
\cpsystems@basecprule{#1}{#2}{#3}{#4}{#5}{(\arabic{cpsystems@RuleNum})}
}
% \end{macrocode}
% \end{macro}
%
% \begin{macro}{\cpfunc}
% Command for declaring a cP~systems functor.
% The first argument is the symbol for the functor itself, and the second argument is the objects contained inside the functor.
% \begin{macrocode}
\newcommand{\cpfunc}[2]{
\trim@spaces@noexp{#1\cpsystems@functorparens{#2}}
}
% \end{macrocode}
% \end{macro}
%
% \begin{macro}{\cpsystems@basecprule}
% For writing out rules inside a |cpruleset| environment.
% Required arguments are, in order, beginning state name; LHS of rule; the label to be applied to the arrow; the ending state name; the RHS of the rule.
% \begin{macrocode}
\newcommand{\cpsystems@basecprule}[6]{
\trim@spaces@noexp{#1 & #2 & \rightarrow_{#3} & #4 & #5 & #6\\}
}
% \end{macrocode}
% \end{macro}
%
% \begin{macro}{\cpsystems@functorparens}
% To ensure that brackets resize themselves automatically in functors.
% \begin{macrocode}
\newcommand{\cpsystems@functorparens}[1]{
\perfectunary{IncreaseHeight}(){#1}
}
% \end{macrocode}
% \end{macro}
%
% \iffalse
%</package>
% \fi
%
% \Finale
%
In case versions matter, I am using MikTex to run this, and it seems to be reporting its version as 20.6.29. AmsMath is version 2.17e. The 'tools' package doesn't have a listed version in the MikTex console but is dated with 'Tue Feb 4 10:11:41 2020'.
Can you see what the problem is? I imagine it is probably some trivial issue of a misplaced character or something, but I have been unable to figure this out. (I'm also open to suggestions on other aspects of the package if someone is keen enough :) )
EDIT: I began to wonder if the perfectcut package actually had anything to do with this problem, and I'm not sure that it does in actuality. To test this, I removed the \RequirePackage{perfectcut} line and modified the definition of cpsystems@cpfunctorparens to simply (#1). I still get the exact same error. Leaving perfectcut in, but changing the cpruleset block to just:
\begin{cpruleset}
\cpfunc{a}{\cpfunc{b}{\cpfunc{c}{d}}}
\end{cpruleset}
gives me exactly the expected behaviour. That said, I did also try to exclude the requirepackage line for perfectcut, but continue using perfectunary to define cpfunc, and didn't seem to experience any errors with it, so I'm not 100% sure I was doing everything correctly. Does anybody have any suggestions on what I should do to test this further to determine the problem precisely?
