Cfxtrjtrk

Please consider the following MWE :

documentclass{article}



newcommand{mymargin}{hspace*{3em}}

newcommand{innerbox}[1]{mymarginfbox{#1}mymargin}

newcommand{outerbox}[1]{fbox{#1}}



begin{document}



test innerbox{Hello} test% OK



test outerbox{innerbox{Hello} test innerbox{Hello} test innerbox{Hello}}%   I don't want space at beginning and end of box



test outerbox{fbox{Hello}mymargin{} test innerbox{Hello} test mymarginfbox{Hello}}%   what i'd like



end{document}

(actually, the definitions of boxes are more complex but I think that doesn't change anything to the logic)

I'd like the use of innerbox inside outerbox not to induce spaces at the beginning and at the end of the box.

I suppose i should expand argument #1 (once got rid of the unnecessary spaces) from outerbox and detect if the first and last token are equal mymargin and then make the necessary changes but I really don't know how to do it. Any ideas?

You can check (ignoring spaces) whether the first token in the argument of outerbox is innerbox and, in this case, insert a negative space for compensation.

At the end you can recursively remove all glue nodes.

documentclass{article}



newcommand{mymarginwidth}{3em}

newcommand{mymargin}{hspace*{mymarginwidth}}

newcommand{negmymargin}{hspace*{-mymarginwidth}}



newcommand{innerbox}[1]{mymarginfbox{#1}mymargin}

makeatletter

newcommand{outerbox}[1]{%

  fbox{%

    @ifnextcharinnerbox{negmymargin}{}#1%

    forever@unskip

  }%

}

newcommand{forever@unskip}{%

  ifnumlastnodetype=11

    expandafterunskipexpandafterforever@unskip

  fi

}

makeatother



begin{document}



test innerbox{Hello} test



test outerbox{innerbox{Hello} test innerbox{Hello} test innerbox{Hello}}



test outerbox{fbox{Hello}mymargin{} test innerbox{Hello} test mymarginfbox{Hello}}



test outerbox{test innerbox{Hello} test innerbox{Hello}}



test outerbox{innerbox{Hello} test innerbox{Hello} test}



test outerbox{ test innerbox{Hello} test innerbox{Hello} }



test outerbox{ innerbox{Hello} test innerbox{Hello} test }



end{document}

This version omits the space if innerbox is in any hbox, not just outerbox

documentclass{article}



newcommand{mymargin}{hspace*{3em}}

newcommand{innerbox}[1]{ifhmodeifinnerelsemymarginfififbox{#1}ifhmodeifinnerelsemymarginfifi}

newcommand{outerbox}[1]{fbox{#1}}



begin{document}



test innerbox{Hello} test% OK



test outerbox{innerbox{Hello} test innerbox{Hello} test innerbox{Hello}}%   I don't want space at beginning and end of box



test outerbox{fbox{Hello}mymargin{} test innerbox{Hello} test mymarginfbox{Hello}}%   what i'd like



end{document}

egreg notes that you may not be what you wanted, so..

documentclass{article}



newcommand{mymargin}{hspace*{3em}}

newcommand{innerbox}[1]{ifhmodeifnumlastpenalty=-1elsemymarginfififbox{#1}mymargin}

newcommand{outerbox}[1]{fbox{penalty-1#1unskipunskip}}



begin{document}



test innerbox{Hello} test% OK



test outerbox{innerbox{Hello} test innerbox{Hello} test innerbox{Hello}}%   I don't want space at beginning and end of box



test outerbox{fbox{Hello}mymargin{} test innerbox{Hello} test mymarginfbox{Hello}}%   what i'd like



end{document}