“Missing Number” error when using “switch” in “boolexpr”

Question

\pdfoutput=1
\documentclass[12pt]{amsart}
\usepackage{boolexpr}

\def \p{1}
\def \q{1}

\begin{document}
\switch[\p=]
\case{\q}abc
\endswitch
def
\end{document}

Compiling the above I get the following error

! Missing number, treated as zero.
<to be read again> 
                   \bex@=0 truepart 
l.12 \endswitch

But if we change the definition to

\def \q{2}

or change the line to

\switch[1=]

it will be OK. But only change the line to

\case{1}abc

yields the same error.

Any idea why this happens? Thank you in advance.

Answer 1

It seems not to be well documented, but the examples show that a counter value is expected. You can fool the package by using \numexpr:

\switch[\numexpr\p\relax=]
\case{\q} abc
\endswitch

The problem is that one has to "announce" boolexpr the type of test to be performed in some way; also

\switch[\number\p=]

works.

Answer 2

use counters instead of macros:

\documentclass{amsart}
\usepackage{boolexpr}
\newcounter{p}\setcounter{p}{1}
\newcounter{q}\setcounter{q}{1}

\begin{document}
\switch[\value{p}=]
\case{\value{q}} abc
\endswitch
def
\end{document}