Make ly:make-unpure-pure-container accept a single callback

Make ly:make-unpure-pure-container accept a single callback

Like with fixed values, this gets duplicated for the pure value as
well, but converted into a three-argument callback.

[MikeSol, 2013-02-21 19:35:35]

LGTM, with one suggestion: the difference between unpure and pure functions in
LilyPond is that unpure functions accept n arguments whereas pure functions
accept n+2. This shortcut you're proposing only works when n=1, which you
document, but it'd be nice if it worked for an arbitrary number of input
arguments.  It'd only be possible to do this, though, if there were a way in C++
to determine the number of arguments a Scheme function took.

[dak, 2013-02-21 19:54:00]

On 2013/02/21 19:35:35, MikeSol wrote:
> LGTM, with one suggestion: the difference between unpure and pure functions in
> LilyPond is that unpure functions accept n arguments whereas pure functions
> accept n+2. This shortcut you're proposing only works when n=1, which you
> document, but it'd be nice if it worked for an arbitrary number of input
> arguments.  It'd only be possible to do this, though, if there were a way in
C++
> to determine the number of arguments a Scheme function took.

Nonsense.  That's what the rest argument is for.  I'll submit an amended
version.

[dak, 2013-02-21 20:07:36]

Allow arbitrary argument number

[dak, 2013-02-21 23:11:19]

Change function signature to make for better error behavior