Strange difference between Lilypond and Guile plain

[R. Mattes]

Dear list,

I just stumbled over a strange problem. I'm trying to use some of
my guile code from within Lilypond. When trying to import some of
my macros (when and unless) into Lilypond I get the following error:

,---- LilyPond RELP ---------------------------------
| guile> (load "syntactic-shugar.scm")
| <unnamed port>: In expression (void):
| <unnamed port>: Wrong type to apply: #<Music function #<procedure #f (parser
location arg)>>
| ABORT: (misc-error)
`----

Here ias the code:

,---- file syntactic-shugar.scm ---------------------
| (use-syntax (ice-9 syncase))
|
| (define-syntax when
|   (syntax-rules ()
|     ((when condition expression ...)
|      (if condition (begin expression ...)))))
|
| (define-syntax unless
|   (syntax-rules ()
|     ((unless condition expression ...)
|      (if (not condition) (begin expression ...)))))
`----

The same code works without problems in guile itself.

Lilypond version: "2.19.5"
Guile version: "1.8.8"

Any idea what's going on?

 TIA Ralf Mattes