[texhax] macro expansion and \input

[Neal H. Walfield]

Hi,

I have a number of generated files containing latex snippets.  So far,
I've include them in my document using \input.  But, to make life a
bit easier, I want to use a macro to generate the full filenames on
the fly.  This is resulting in some macro expansion issues, which I
don't understand.  The following is what I want to do:

  \documentclass{article}
  
  \begin{document}
  
  % My general-purpose macro.
  \def\mutate#1{
    \def\helper{#1}
    \helper
  }
  
  \input{\mutate{23}}
  
  \end{document}

But, this results in:

  ! Missing control sequence inserted.
  <inserted text> 
                  \inaccessible 
  l.11 \input{\mutate{23}}

It seems like \input is protecting its input from expansion.
Interestingly, simple expansion, such as the following, works fine:

  \documentclass{article}

  \begin{document}

  \def\filename{12}
  \input{\filename}

  \end{document}

Based on this observation, I tried to preexpand \input's argument:

  \documentclass{article}
  
  \begin{document}
  
  % My general-purpose macro.
  \def\mutate#1{
    \def\helper{#1}
    \helper
  }
  
  \def\myinput#1{
    \edef\filename{#1}
    \input{\filename}
  }

  \myinput{\mutate{23}}
  
  \end{document}

But, this results in a different error:

  ! Undefined control sequence.
  \mutate #1-> \def \helper 
                            {#1} \helper 
  l.16   \myinput{\mutate{23}}
                              
When expanding \filename, tex wants expands \mutate's \helper control
sequence rather than define it!

Now, I'm stuck and would welcome some help...


Thanks,

Neal