Re: Basic functions

[Jean Abou Samra]

Le 15/05/2021 à 19:49, Jenifer Tribe a écrit :

I want to include a change of midi tempo at various points in a score, using something like

  \setSpeed #2 #120

where 

setSpeed =

  #(define-music-function

      (parser location scale speed)

      (number? number? )

    #{

       \set Score.tempoHideNote = ##t

       \tempo scale = speed

    #}

  )

I'm still using 2.18 I'm afraid, which still used the parser and location parameters..

I'm assuming this should be a music function rather than markup, but perhaps my arguments aren't numbers.

In this case the function is hardly worth it, but I want to base more complicated routines on it, and have failed at the first hurdle!

There are two mistakes here:

- In the function, scale and speed are interpreted as strings.
  You want $scale and $speed (the reason for using $ instead
  of # is explained in [1]).

- The scale argument is a duration, not a number (you can do
  \tempo 4. = 120 for instance).

Corrected version:

\version "2.23.3"

setSpeed =
#(define-music-function
    (parser location scale speed)
    (ly:duration? number?)
  #{
     \set Score.tempoHideNote = ##t
     \tempo $scale = $speed
  #})


\score {
  {
    \setSpeed 4. 4
    c
  }
  \layout { }
  \midi { }
}

There is also the possibility of doing

\layout {
  \context {
    \Score
    tempoHideNote = ##t
  }
}

to set tempoHideNote globally (read [2]), and then you
can just use the normal \tempo command in the music.

Best,
Jean

[1] https://extending-lilypond.readthedocs.io/en/latest/lily-and-scheme.html#hash-vs-dollar
[2] http://lilypond.org/doc/v2.22/Documentation/notation/changing-context-default-settings