Re: tempo percentage

[Gianmaria Lari]

On 27 November 2017 at 09:32, David Kastrup <address@hidden> wrote:

Gianmaria Lari <address@hidden> writes:

> On 27 November 2017 at 07:39, Gianmaria Lari <address@hidden>
> wrote:
>
>>
>> On 27 November 2017 at 00:24, David Kastrup <address@hidden> wrote:
>>
>>> Gianmaria Lari <address@hidden> writes:
>>>
>>> > On 8 November 2017 at 18:15, David Kastrup <address@hidden> wrote:
>>> >
>>> >> Gianmaria Lari <address@hidden> writes:
>>> >>
>>> >> > Talking about midi, is there any way to to reduce or increase the
>>> tempo
>>> >> of
>>> >> > some measures by a certain percentage instead of setting it to an
>>> >> absolute
>>> >> > value?
>>>
>>
>
> Another question. It would be also useful to have a function that increase
> the tempo by a certain quantity (instead of a certain factor).
>
> I tried to modify the previous code in many ways using moment-add and
> make-moment but without success. This is an example that does not work:
>
> (ly:moment-add (ly:context-property c 'tempoWholesPerMinute) value)
>
>
> Any suggestion?

Scheme has no types known as "quantity".  Neither has LilyPond.  You
don't show how you get at `value'.

<URL:http://lilypond.org/tiny-examples.html>

For example:

\version "2.19.80"

increaseTempo =

#(define-music-function (value)(number?) #{

  \context Timing \applyContext

  #(lambda (c)

     (set! (ly:context-property c 'tempoWholesPerMinute)

           (ly:moment-add (ly:context-property c 'tempoWholesPerMinute) value)

           ))

   #} )

\score {

  {

    \tempo 4=100

    a b \increaseTempo 50 c' d'

  }

  \layout {} \midi{}

}