Kdtyjb

I'd like to generate an environment that changes a bit according to an argument given for it. The reason is having different locales in the document. I have defined a command, EmitLanguageStr that determines the argument to otherlanguage according to the argument that was passed. For example, EmitLanguageStr[en] -> english. See these questions for further context: [ 1, 2 ]. Here's the environment stripped down.

renewenvironment{abstract}[1][en]{%

    section*{EmitAbstractStr[#1]}

    begin{otherlanguage}{EmitLanguageStr[#1]}

        @authorpar

        textbf{EmitTitle[#1]}par

}{%

    end{otherlanguage}

}

Turns out other people have had the same problem (Q), but the solution did not quite work for me. The answer suggests that wrapping the environment in one of two ways would allow the argument to be expanded:

% Create a macro

newcommandtestlang{english}



% Expand the argument once:

newenvironment{Otherlanguage}[1]{%

    expandafterotherlanguageexpandafter{#1}%

}{endotherlanguage}



% Alternative: argument is fully expanded

newenvironment{Otherlanguage}[1]{%

    begingroup

    edeftemp{endgroupnoexpandotherlanguage{#1}}%

    temp

}{endotherlanguage}



% usage    

begin{Otherlanguage}{testlang}

    ...

end{Otherlangauge}

First, without these wrappers, babel gives an error message that the language EmitLanguageStr[en] is not defined. That was addressed in the linked question. However, the solutions presented produce another kind of error: Use of EmitLanguageStr doesn't match its definition.

How can the command be properly expanded?

Here's a complete example of the situation. This works, but by switching the argument of Otherlanguage to the one in the comment the described error is thrown.

documentclass[a4paper,12pt]{article}



usepackage{ifthen}

usepackage{pgffor}



makeatletter



newcommandSetDefaultValue[2]{%

    global@namedef{#2:#1}{%

        {scriptsize (Use {tttextbackslash #2[#1]} to replace this text.)}%

    }%

}



newcommandMakeLocaleVar[2][en,fi]{%

    foreach n in {#1}{%

        expandafterSetDefaultValueexpandafter{n}{#2}

    }%

    expandafternewcommandcsname #2endcsname[2][]{%

        ifthenelse{equal{##1}{}}{%

            foreach n in {#1}{%

                global@namedef{#2:n}{##2}%

            }%

        }{%

            global@namedef{#2:##1}{##2}%

        }%

    }%

    expandafternewcommandcsname Emit#2endcsname[1][en]{@nameuse{#2:##1}}%

}



% Variables set in document

MakeLocaleVar{Title}

MakeLocaleVar{Year}



%newenvironment{Otherlanguage}[1]{%

%   expandafterotherlanguageexpandafter{#1}%

%}{endotherlanguage}



newenvironment{Otherlanguage}[1]{%

    begingroup

    edeftemp{endgroupnoexpandotherlanguage{#1}}%

    temp

}{endotherlanguage}



MakeLocaleVar{AbstractStr}

AbstractStr[en]{ABSTRACT}

AbstractStr[fi]{TIIVISTELMÄ}



MakeLocaleVar{LanguageStr}

LanguageStr[en]{english}

LanguageStr[fi]{finnish}



renewenvironment{abstract}[1][en]{%

    section*{EmitAbstractStr[#1]}

    begin{Otherlanguage}{english}%EmitLanguageStr[#1]

        @authorpar

        textbf{EmitTitle[#1]}par

        EmitYearpar

        par

    }{%

    end{Otherlanguage}

}



makeatother



usepackage[utf8]{inputenc}

usepackage[T1]{fontenc}

usepackage[finnish, english]{babel}



author{Handsome Devil}

Year{2019}



Title[en]{Title in English}

Title[fi]{Otsikko suomeksi}



begin{document}

selectlanguage{english}



begin{abstract}

    Abstract environment in English.

end{abstract}



begin{abstract}[fi]

    Abstract environment in Finnish.

end{abstract}

end{document}

MakeLocaleVar{LanguageStr} causes EmitLanguageStr to be defined as:

newcommandEmitLanguageStr[1][en]{@nameuse{LanguageStr:#1}}%

EmitLanguageStr processes an optional argument.

If you look at EmitLanguageStr via showEmitLanguageStr, you'll find:

> EmitLanguageStr=macro:

->@protected@testopt EmitLanguageStr \EmitLanguageStr {en}.

Looking at @protected@testopt yields:

> @protected@testopt=macro:

#1->ifx protect @typeset@protect expandafter @testopt else @x@protect #1

fi .

Looking at @testopt yields:

> @testopt=long macro:

#1#2->kernel@ifnextchar [{#1}{#1[{#2}]}.

Looking at kernel@ifnextchar yields:

> kernel@ifnextchar=long macro:

#1#2#3->let reserved@d =#1def reserved@a {#2}def reserved@b {#3}futurele

t @let@token @ifnch .

Looking at @ifnch yields:

> @ifnch=macro:

->ifx @let@token @sptoken let reserved@c @xifnch else ifx @let@token 

reserved@d let reserved@c reserved@a else let reserved@c reserved@b fi 

fi reserved@c .

Looking at @xifnch yields:

> @xifnch=macro:

 ->futurelet @let@token @ifnch .

As you can see a lot of playing around with non-expandable let- and futurelet-assignments is involved into the checking for the presence of the optional argument via kernel@ifnextchar [.

Therefore EmitLanguageStr does not only deliver those character tokens that form the name of the language. It also yields a lot of unexpandable assignment-tokens like let and futurelet for checking for the presence of the optional argument.

These tokens won't vanish within a pure-expansion-context while obtaining the name of the language for passing it as argument to an environment would be a pure expansion context.
After expansion these unexpandable assignment-tokens remain in the token-stream because while expansion takes place in (La)TeX's "gullet",
the carrying out of assignments takes place in (La)TeX's "stomach".

So in short:

As long as EmitLanguageStr processes an optional argument whereby the techniques for detecting the presence of an optional argument themselves involve non-expandable assignment-tokens which don't vanish during expansion, you can't use EmitLanguageStr in pure-expansion-contexts for obtaining only those tokens that form the name of the language.

But you can, e.g., create a variant of EmitLanguageStr with an additional argument holding tokens to which the emitted string is to be passed as argument. I call that macro PassLanguageStrTo:

documentclass[a4paper,12pt]{article}



usepackage{ifthen}

usepackage{pgffor}



makeatletter



newcommandSetDefaultValue[2]{%

    global@namedef{#2:#1}{%

        {scriptsize (Use {tttextbackslash #2[#1]} to replace this text.)}%

    }%

}



newcommandPassFirstToSecond[2]{#2{#1}}%



newcommandMakeLocaleVar[2][en,fi]{%

    foreach n in {#1}{%

        expandafterSetDefaultValueexpandafter{n}{#2}%%%%

    }%

    expandafternewcommandcsname #2endcsname[2][]{%

        ifthenelse{equal{##1}{}}{%

            foreach n in {#1}{%

                global@namedef{#2:n}{##2}%

            }%

        }{%

            global@namedef{#2:##1}{##2}%

        }%

    }%

    expandafternewcommandcsname Emit#2endcsname[1][en]{@nameuse{#2:##1}}%

    expandafternewcommandcsname Pass#2Toendcsname[2][en]{%

      expandafterexpandafterexpandafterPassFirstToSecond

      expandafterexpandafterexpandafter{csname#2:##1endcsname}{##2}%

    }%

}



% Variables set in document

MakeLocaleVar{Title}

MakeLocaleVar{Year}





MakeLocaleVar{AbstractStr}

AbstractStr[en]{ABSTRACT}

AbstractStr[fi]{TIIVISTELMÄ}



MakeLocaleVar{LanguageStr}

LanguageStr[en]{english}

LanguageStr[fi]{finnish}



renewenvironment{abstract}[1][en]{%

    section*{EmitAbstractStr[{#1}]}%%%%

    PassLanguageStrTo[{#1}]{begin{otherlanguage}}%

        @authorpar

        textbf{EmitTitle[{#1}]}par

        EmitYearpar

        par

    }{%

    end{otherlanguage}%%%%

}



makeatother



usepackage[utf8]{inputenc}

usepackage[T1]{fontenc}

usepackage[finnish, english]{babel}



author{Handsome Devil}

Year{2019}



Title[en]{Title in English}

Title[fi]{Otsikko suomeksi}



begin{document}

selectlanguage{english}



begin{abstract}

    Abstract environment in English.

end{abstract}



begin{abstract}[fi]

    Abstract environment in Finnish.

end{abstract}

end{document}