Syntax issue with optional argument inside optional argument

Question

The following source gives the expected results, as shown:

\documentclass[12pt]{article}

\usepackage{amsmath}
\usepackage{xstring}

\usepackage[refpage,nocfg]{nomencl}
\renewcommand*{\pagedeclaration}[1]{\unskip, #1}

\newcommand{\nom}[4][]{%
  \IfStrEqCase{#1}{%
  {logic}{\nomenclature[a#4]{#2}{#3}}%
  {set}{\nomenclature[e#4]{#2}{#3}}%
  }%
%[\nomenclature[z#4]{#2}{#3}]%
}

\makenomenclature

\begin{document}

\nom[logic]{$p\implies q$}{if $p$ then $q$}{1}
\nom[set]{$x \in A$}{$x$ is an element of $A$}{1}

\printnomenclature[0.75in]

\end{document}

$Output OK without default for \IfStrEqCase other cases$

But if the comment sign is removed from the beginning of the line

%[\nomenclature[z#4]{#2}{#3}]%

then I'm getting strange results for output—extra insertions in body of the document output:

$Unexpected output with other-cases value for \IfStrEqCase$

What's wrong with my syntax? I thought that

[\nomenclature[z#4]{#2}{#3}]

would constitute the "other-cases code" for the entire \IfStrEqCase construction.

Note: This is an extract. In the actual document, I have several nomenclature "groups" defined by means of \nomgroup, each group with its own header. The optional (1st) argument of the command \nom will indicate the group to which that \nomenclature item belongs.

Does this answer your question? Bug? LaTeX misparses nested optional arguments — user202729, Nov 07 '21 at 15:17
@user202729: Yes it answers my question, as does Pieter van Oostrum's answer there that I already accepted. — murray, Nov 08 '21 at 19:58

score 5 · Accepted Answer · answered Nov 22 '16 at 21:34

5

Your default argument

[\nomenclature[z#4]{#2}{#3}]

has a ] inside (after #4), so that finishes the argument, and the rest is just text that is inserted in the document.

Solution: enclose it in braces:

 [{\nomenclature[z #4]{#2}{#3}}]%

answered Nov 22 '16 at 21:34

Pieter van Oostrum

16,203

Ulrich Diez · Answer 2 · 2016-11-23T00:18:46.763

You cannot nest optional arguments (that come in catcode-12-brackets) like mandatory arguments (that come in catcode-1-opening braces and catcode-2-closing-braces).

Optional arguments are handled as delimited arguments with opening brackets and closing brackets as argument-delimiters.
When nesting optional arguments, (La)TeX' delimited argument-mechanism doesn't "know" how to match opening and closing brackets correctly.

If you wish to nest optional arguments within optional arguments, make sure to wrap the content of entire optional arguments into an additional pair of braces. When optional arguments are wrapped into a pair of braces, these braces get silently removed by LaTeX before further processing these optional arguments. So these braces are not harmful.

E.g.,

\documentclass[12pt]{article}

\newcommand\Foo[2][Optional]{%
  This is Foo' s optional:\parbox[t]{.6\textwidth}{(\\#1\\)}\\%
  This is Foo's mandatory:\parbox[t]{.6\textwidth}{(\\#2\\)}%
}

\newcommand\Bar[2][Optional]{%
  This is Bar's optional:(#1)\\%
  This is Bar's mandatory:(#2)%
}

\begin{document}

\noindent
% This works because \Foo's optional argument is nested into an
% additional pair of braces.
\Foo[{\Bar[BarOptional]{BarMandatory}}]{FooMandatory}

% This does not work as (La)TeX' delimited argument-mechanism doesn't
% "know" how to match opening and closing brackets correctly:
% \Foo[\Bar[BarOptional]{BarMandatory}]{FooMandatory}

\end{document}

Only after having obtained this knowledge, it is obvious that

\newcommand{\nom}[4][]{%
  \IfStrEqCase{#1}{%
  {logic}{\nomenclature[a#4]{#2}{#3}}%
  {set}{\nomenclature[e#4]{#2}{#3}}%
  }%
  [\nomenclature[z#4]{#2}{#3}]%
}

should be changed to:

\newcommand{\nom}[4][]{%
  \IfStrEqCase{#1}{%
  {logic}{\nomenclature[a#4]{#2}{#3}}%
  {set}{\nomenclature[e#4]{#2}{#3}}%
  }%
  [{\nomenclature[z#4]{#2}{#3}}]%
}

Your entire example becomes something like:

\documentclass[12pt]{article}

%\IfFileExists{\jobname.nlo}%
%             {\immediate\write18{makeindex \jobname.nlo -s nomencl.ist -o \jobname.nls}}%
%             {}

\usepackage{amsmath}
\usepackage{xstring}

\usepackage[refpage,nocfg]{nomencl}
\renewcommand*{\pagedeclaration}[1]{\unskip, #1}

\newcommand{\nom}[4][]{%
  \IfStrEqCase{#1}{%
  {logic}{\nomenclature[a#4]{#2}{#3}}%
  {set}{\nomenclature[e#4]{#2}{#3}}%
  }%
  [{\nomenclature[z#4]{#2}{#3}}]%
}

\makenomenclature

\begin{document}

Some text for ensuring that \LaTeX' output-routine comes into action.\\
Otherwise .nlo-files do not get generated.

\nom[logic]{$p\implies q$}{if $p$ then $q$}{1}
\nom[set]{$x \in A$}{$x$ is an element of $A$}{1}
\nom{$x =y $}{$x$ and $y$ are different designators for the same item of cognizance}{1}

\printnomenclature%[0.75in]

\end{document}

Syntax issue with optional argument inside optional argument

2 Answers2