loop and input@path

Question

I'm trying to have recursive path in the command \input@path, but it seems to be impossible (as I read, I'm with the TexLive 2012 and Linux).

So I had the following idea, make a loop in \input@path, but it doesn't work and I don't know why ...

This is what I did :

\newcounter{path}
\setcounter{path}{0}
\def\nom{%
  \ifcase\thepath Cours%
  \or Livres%
  \fi
}
\def\input@path{%
 \loop \ifnum \thepath<3
   {~/Exercices/\nom/Derivee/}
 \stepcounter{path} \repeat
}

If someone have an idea, it will be very helpful.

Answer 1

The format of \input@path is fixed, each path entry is surrounded by curly braces without further separators. Any other stuff such as loops are forbidden. But it is possible to add entries:

\makeatletter
\newcounter{path}
\setcounter{path}{0}
\newcommand*{\nom}{%
  \ifcase\value{path}%
    Cours% 0
  \or
    Livres% 1
  \or
    Two% 2
  \fi
}
\@ifundefined{input@path}{%
  \let\input@path\@empty
}{}
\loop
\ifnum\value{path}<3 %
  \edef\input@path{%
    \input@path
    {\string~/Exercises/\nom/Derivee/}%
  }%
  \stepcounter{path}%
\repeat
\typeout{input@path: \input@path}
\makeatother

Some remarks:

• The input strings are expanded by \edef, because sooner or later they are expanded anyway. The tilde ~ is usually an active character, to prevent expansion, it is prefixed by \string that converts the active to a non-active character (with catcode 12).

• The example uses \value{<counter>} instead of \the<counter>, because the latter form is intended for printing and might not always expand to a plain arabic number.

• The definition for number 2 in \ifcase was missing.