scm functions scope and arguments

[VSD]

Hi,

I've made a set of scheme functions to simplify the use of custom fret  
diagrams in scores. Here is a sample file of how it works:

%%%%%%%%% start of sample file

\version "2.5.31" % Win XP

#(def-markup-command (E-one layout props arg) (markup?)
  (let
    (
      (definition-list
        (fret-parse-definition-string
          (cons '((thickness . 0.8) (size . 1.05)) props)
          "h:3;f:1;6-o;5-2-2;4-2-3;3-1-1;2-o;1-o;"
        )
      )
    )
    (make-fret-diagram layout (car definition-list) (cdr definition-list)))
)

\score
{
  \new Staff
  {
    a4^\markup \E-one "" b c d
  }
}

%%%%%%%% EOF

This code works fine as long as E-one is defined inside the file  
"fret-diagrams.scm" (without the starting "#"). But if I define it outside  
that file (e.g. in the calling ly file as in the given example), then  
lilypond complains:

"ERROR: Unbound variable: fret-parse-definition-string"

It somehow doesn't find the definition of this function (which is defined  
inside "fret-diagrams.scm" too).

Does anybody know how to succesfully define and use the function E-one  
outside "fret-diagrams.scm", e.g. inside an auxiliary private file named  
"fret-diag-utils.scm"?

This way I wouldn't need to "dirty" the installed "fret-diagrams.scm"  
file, so I wouldn't have to update it after each intermediate lilypond  
upgrade.

Yet one more thing: How could I define the E-one function so it takes no  
arguments?

I've tried

#(def-markup-command (E-one layout props)
   (...)
)

but this doesn't work:

"ERROR: In procedure memoization:
ERROR: Missing expression in (define-private (E-one-markup layout props))"

The goal is to call \E-one instead of \E-one ""

Any hints appreciated. Thanks in advance,

Vincent