Pass a macro as parameter to package xsim

Question

I am trying to write a document using the xsim package. It is divided into chapters and each contains its own exercises and its solutions, at the end of each.

At present, the structure of each chapter is written by hand as in ChManual.tex but I would like to use something like macroChapter.tex, which uses \thechapter as parameter to invoke and print the collections defined for xsim.

The following MWE works if you use ChManual.tex, if you uncomment the lines %\input{macroChapter.tex} of chapters 1 and 2, it does not work showing an error: unknown-collection "collCh\thechapter".

\documentclass{report}

\usepackage{filecontents}

\usepackage{xsim}

\DeclareExerciseCollection{collCh1}
\DeclareExerciseCollection{collCh2}
\DeclareExerciseCollection{collChManual}

\begin{filecontents}{Ch1.tex}

    \begin{exercise}
    This is exercise 1 from chapter \thechapter.
    \end{exercise}

    \begin{solution}
    This is solution of exercise 1 from chapter \thechapter.
    \end{solution}

\end{filecontents}

\begin{filecontents}{Ch2.tex}

    \begin{exercise}
    This is exercise 1 from chapter \thechapter.
    \end{exercise}

    \begin{solution}
    This is solution of exercise 1 from chapter \thechapter.
    \end{solution}

    \begin{exercise}
    This is exercise 2 from chapter \thechapter.
    \end{exercise}

    \begin{solution}
    This is solution of exercise 2 from chapter \thechapter.
    \end{solution}

\end{filecontents}

\begin{filecontents}{ChManual.tex}

    \begin{exercise}
    This is exercise 1 from chapter \thechapter (Manual).
    \end{exercise}

    \begin{solution}
    This is solution of exercise 1 from chapter \thechapter (Manual).
    \end{solution}

    \begin{exercise}
    This is exercise 2 from chapter \thechapter (Manual).
    \end{exercise}

    \begin{solution}
    This is solution of exercise 2 from chapter \thechapter (Manual).
    \end{solution}

\end{filecontents}

\begin{filecontents}{macroChapter.tex}

    This is chapter \thechapter.

    \collectexercises{collCh\thechapter}

    \input{Ch\thechapter.tex}

    \collectexercisesstop{collCh\thechapter}

    \printcollection[print=exercises]{collCh\thechapter}

    Bla bla bla bla bla bla bla bla bla bla bla.

    \printsolutions[chapter=\thechapter,collection=collCh\thechapter]

\end{filecontents}

\begin{filecontents}{manualChapter.tex}

    This is chapter Manual.

    \collectexercises{collChManual}

    \input{ChManual.tex}

    \collectexercisesstop{collChManual}

    \printcollection[print=exercises]{collChManual}

    Bla bla bla bla bla bla bla bla bla bla bla.

    \printsolutions[chapter=3,collection=collChManual]

\end{filecontents}

\begin{document}

\chapter{One}

%\input{macroChapter.tex}

\chapter{Two}

%\input{macroChapter.tex}

\chapter{Manual}

\input{manualChapter.tex}

\end{document}

Answer 1

This is yet another variant of “expand the argument before you pass it to the next macro”.

Specifically you want x variants of the macros \xsim_start_collection:n, \xsim_stop_collection:n and \xsim_print_collection:nn as well as adapted user commands:

\ExplSyntaxOn
\RenewDocumentCommand \collectexercises {t!m}
  {
    \IfBooleanTF {#1}
      { \xsim_start_collection:x {#2} }
      { \xsim_start_collection:n {#2} }
  }

\RenewDocumentCommand \collectexercisesstop {t!m}
  {
    \IfBooleanTF {#1}
      { \xsim_stop_collection:x {#2} }
      { \xsim_stop_collection:n {#2} }
  }

\RenewDocumentCommand \printcollection {t!O{}m}
  {
    \IfBooleanTF {#1}
      { \xsim_print_collection:nx {#2} {#3} }
      { \xsim_print_collection:nn {#2} {#3} }
  }

\cs_generate_variant:Nn \xsim_start_collection:n  {x}
\cs_generate_variant:Nn \xsim_stop_collection:n   {x}
\cs_generate_variant:Nn \xsim_print_collection:nn {nx}

\ExplSyntaxOff

Then use (notice the exclamation marks):

\begin{filecontents}{macroChapter.tex}

    This is chapter \thechapter.

    \collectexercises!{collCh\thechapter}

    \input{Ch\thechapter.tex}

    \collectexercisesstop!{collCh\thechapter}

    \printcollection![print=exercises]{collCh\thechapter}

    Bla bla bla bla bla bla bla bla bla bla bla.

    \printsolutions[chapter=\thechapter,collection=collCh\thechapter]

\end{filecontents}

BTW: I'd rather use \arabic{chapter} instead of the \thechapter in the collection names – you want the number and not the printed output!