Re: trying to create a function with different pitches and different rhythms

[Aaron Hill]

On 2018-06-23 01:14, Stefan Thomas wrote:
> Dear community,
> I want to create a function, which adds automatically a crescendo from 
> ppp
> to pp to two tied pitches with different durations.
> What  I dont understand:
> I can create a function with the same pitch and different durations, I 
> can
> also create a function with diferent pitches and same durations, but if
> both are choosen freely, I can't do it. Can someon give me a hint, 
> whats
> wrong with the code?
>
> \version "2.18.2"
>
> \layout {  \context { \Voice \override Hairpin.minimum-length = #10 }  
> }
>
> %different durations, different  pitches, this doesn't work, why?
> fadeIn = #(define-music-function (parser location PITCH durA durB)
> (ly:pitch?  ly:duration? ly:duration?)
>              #{
>                  $PITCH  $durA  \<\ppp ~  $PITCH $durB \pp
>                #})
> \new Staff { \fadeIn c' 4 2. }

For reference, this works just fine against 2.19.81.  However, on 2.18.2 
it errors:

> input.ly:11:22: error: wrong type for argument 1.  Expecting pitch, 
> found (make-music (quote NoteEvent) (quote duration) (ly:make-duration 
> 2 0 1) (quote pitch) (ly:make-pitch 0 0 0))
> \new Staff { \fadeIn
>                      c' 4 2. }

Looks like 2.18.2 is trying to read `c' 4` as a single argument.  
Consider the following:

%%%%
  fadeIn = #(define-music-function (parser location PITCH DUMMY durA 
durB)
    (ly:pitch? string? ly:duration? ly:duration?)
    #{ $PITCH $durA \<\ppp ~ $PITCH $durB \pp #})
  \new Staff { \fadeIn c' "" 4 2. }
%%%%

Forcing a dummy argument between the pitch and duration seems to allow 
2.18.2 to parse this.

-- Aaron Hill