Doc: Corrected doc string for ly:dimension?

Doc: Corrected doc string for ly:dimension?

ly:dimension? is a predicate - it does not return a number.

[davidsg, 2020-01-25 16:12:45]

It isn't clear to me how a dimension is different from a normal number, but the
current doc string seems to be incorrect all the same.

[thomasmorley651, 2020-01-26 10:45:11]

I don't see any difference to checking for a number either. Thus "distinguish"
feels strange.

Ofcourse it's a predicate, thus
LGTM

Thanks! You can't be motivated to go through the other doc-strings listed in IR
4. Scheme functions ?
:)

[dak, 2020-01-26 11:49:32]

On 2020/01/26 10:45:11, thomasmorley651 wrote:
> I don't see any difference to checking for a number either. Thus "distinguish"
> feels strange.

There was a time when music function predicates determined syntactic decisions
based on what function they pointed to rather than what they evaluated to.  So
people were confused why their user-defined functions, say, number-or-string? ,
did not admit either numbers or strings syntactically.

ly:dimension? never made it to special status in the parser.  In olden times
that would mean that when using it as a music function argument, the respective
number could not be entered as a plain number but would always have to be
preceded with # .  This kind of predicate aliasing serves almost no point any
more (markup? and markup-list? in markups are still treated in that manner,
though).

> Ofcourse it's a predicate, thus
> LGTM
> 
> Thanks! You can't be motivated to go through the other doc-strings listed in
IR
> 4. Scheme functions ?
> :)