Related to my problem for xsim here.

I want to use commands ExOption and ExPart to implement more easily my collection in xsim package. But i'm facing the problem that my commands do not expand in DeclareExerciseCollectionExOption_ExPart. In the aux file i can find this line : XSIM collection:ExOption _ExPart who point to me that there is no expansion.

How can i make my commands expanded before the macros DeclareExerciseCollection and avoid spaces implement by TeX after a macro ? I've read some information about expandafter and edef and i think it can be helpfull but it's the first time i've to deal with those commands.

Here is a MWE :

documentclass[10pt,a4paper]book
usepackage[verbose,clear-aux]xsim


%%Declaration exercices
 edefExOptiondefault
 edefExPartdefault

%%Declaration Collection
 renewcommandExOption5M4
 renewcommandExPartAlgebreFinanciere

 DeclareExerciseCollectionExOption_ExPart %%With custom commands produce wrong output
% DeclareExerciseCollection5M4_AlgebreFinanciere %%With applicable name produce good output
begindocument
chapterWhere i want exercises
%%Collecting exercises
 collectexercisesExOption_ExPart %%With custom commands produce wrong output
 beginexercise
 Can you print me ?
 endexercise
 beginsolution
 Yes, you can !
 endsolution
 collectexercisesstopExOption_ExPart

% collectexercises5M4_AlgebreFinanciere %%With applicable name produce good output
% beginexercise
% Can you print me ?
% endexercise
% beginsolution
% Yes, you can !
% endsolution
% collectexercisesstop5M4_AlgebreFinanciere

%%Print
Output of the command in LaTeX verb|ExOption_ExPart| : ExOption_ExPart


 printcollection5M4_AlgebreFinanciere
enddocument 

With a current version of pdftex (that defines expanded) you can define expanding versions of the commands as shown below.

With older implementations without expanded you can use edef:

newcommandxDeclareExerciseCollection[1]%
 edeftmpnoexpandDeclareExerciseCollection#1tmp

and similarly for the other two commands.

documentclass[10pt,a4paper]book
usepackage[verbose,clear-aux]xsim

newcommandxDeclareExerciseCollection[1]%
 expandafterDeclareExerciseCollectionexpandafterexpanded#1
newcommandxcollectexercises[1]%
 expandaftercollectexercisesexpandafterexpanded#1
newcommandxcollectexercisesstop[1]%
 expandaftercollectexercisesstopexpandafterexpanded#1

%%Declaration exercices
 edefExOptiondefault
 edefExPartdefault

%%Declaration Collection
 renewcommandExOption5M4
 renewcommandExPartAlgebreFinanciere

 xDeclareExerciseCollectionExOption_ExPart %%With custom commands produce wrong output
% DeclareExerciseCollection5M4_AlgebreFinanciere %%With applicable name produce good output
begindocument
chapterWhere i want exercises
%%Collecting exercises
 xcollectexercisesExOption_ExPart %%With custom commands produce wrong output
 beginexercise
 Can you print me ?
 endexercise
 beginsolution
 Yes, you can !
 endsolution
 xcollectexercisesstopExOption_ExPart

% collectexercises5M4_AlgebreFinanciere %%With applicable name produce good output
% beginexercise
% Can you print me ?
% endexercise
% beginsolution
% Yes, you can !
% endsolution
% collectexercisesstop5M4_AlgebreFinanciere

%%Print
Output of the command in LaTeX verb|ExOption_ExPart| : ExOption_ExPart


 printcollection5M4_AlgebreFinanciere
enddocument 

I present two solutions here.

First solution

This is in the same spirit as David Carlisle's solution, except that only one command needs to be defined for everything. You don't need a specific command for DeclareExerciseCollection, for collectexercises, for collectexercisesstop, etc. Also, the command is implemented with LaTeX3—and thus not a fake of David Carlisle's solution. :-)

documentclassbook
usepackage[verbose,clear-aux]xsim
usepackagexparse

ExplSyntaxOn

cs_new_protected:Npn pirooh_call_with_one_arg:Nn #1#2
 
 #1 #2
 

cs_generate_variant:Nn pirooh_call_with_one_arg:Nn Nx 

NewDocumentCommand callWithExpandedArg m m 
 
 % Perform full expansion on what #2 stands for, then call #1
 % with the result.
 pirooh_call_with_one_arg:Nx #1 #2
 

ExplSyntaxOff

newcommand*ExOption5M4
newcommand*ExPartAlgebreFinanciere

callWithExpandedArgDeclareExerciseCollectionExOption_ExPart

begindocument
chapterWhere i want exercises

callWithExpandedArgcollectexercisesExOption_ExPart

beginexercise
 Can you print me ?
endexercise
beginsolution
 Yes, you can !
endsolution

callWithExpandedArgcollectexercisesstopExOption_ExPart

callWithExpandedArgprintcollectionExOption_ExPart
enddocument

Second solution

Here, the approach is different. There is one command to define per argument value, not per xsim command such as DeclareExerciseCollection, collectexercises, collectexercisesstop and printcollection as in David Carlisle's solution. Here, the command callWithPredefinedArg is defined for the argument value 5M4_AlgebreFinanciere (you may want to adapt its name).

This solution isn't better than others, it's just different in spirit. The code does full expansion of ExOption and ExPart when callWithPredefinedArg is defined (this could be changed if needed).

documentclassbook
usepackage[verbose,clear-aux]xsim

newcommand*ExOptiondefault
newcommand*ExPartdefault

renewcommand*ExOption5M4
renewcommand*ExPartAlgebreFinanciere

% This recursively expands ExOption and ExPart and “freezes”
% the result in the definition of callWithPredefinedArg.
edefcallWithPredefinedArg#1#1ExOption_ExPart

% Of course, you could achieve the same with:
%defcallWithPredefinedArg#1#15M4_AlgebreFinanciere

callWithPredefinedArgDeclareExerciseCollection

begindocument
chapterWhere i want exercises

callWithPredefinedArgcollectexercises

beginexercise
 Can you print me ?
endexercise
beginsolution
 Yes, you can !
endsolution

callWithPredefinedArgcollectexercisesstop

callWithPredefinedArgprintcollection

% If you have another chapter/module to start here, you could do
% defcallWithPredefinedArg#1#16N5_GeometrieFinanciere
% callWithPredefinedArgcollectexercises
% etc.
enddocument