Finding files in include paths

[Urs Liska]

Hi all,

how/where is the file searchign with LilyPond's search path is
implemented?

If I write 
  \include "a/relative/path"
the given path is searched for relative to all search paths known to
LilyPond.

Is there a way to do the same in Scheme, say
  (file-visible-to-lilypond "a/relative/path")
to determine whether a target can be found within any LilyPond search
path? Probably the function should return the absolut path, similar to
what kpsewhich does.

I need that to check whether a certain file is present (and then open
it) without knowing the absolute location.

Urs