Re: simple scheme in lilypond

[Jan-Peter Voigt]

Hello,

the $ sign has a special meaning of "instant scheme-expression". An
instant scheme expression is evaluated instantly *and* the result is
observed so that lilypond can decide what to do with it. When lily
receives something that can be treated as a markup from an instant
scheme expression it is handled like \markup {}. But a pure string is
not a core lily-expression like music or markup. Thats the reason (3)
fails with an error. The result of a plain scheme-exression introduced
with # is simply ignored in root context.

HTH
Jan-Peter


Am 27.11.18 um 09:14 schrieb Gianmaria Lari:
> Probably these are very trivial things. Sorry to ask them but would like
> to understand.
> 
> If I write (1):
> 
> 
>     \version "2.19.82"
>     $(object->string (+ 3 2))
> 
> 
> Lilypond is happy and compile to a pdf file showing "5".
> 
> Even this simpler code works... (2)
> 
>     \version "2.19.82"
>     $"Hello"
> 
> 
> and generate a pdf file showing "Hello".
> 
> It is clear to me that $ introduce a scheme expression that is
> evaluated. And in the previous two examples the scheme code is evaluated
> to strings. But I don't understand why lilypond outputs them. If I write
> (3):
> 
>     \version "2.19.82"  
>     "Test"
> 
> 
> this does not compile. So I would think that the "correct" code to
> output evaluated expression in the pdf file should be (4)
> 
> 
>     \version "2.19.82"
>     \markup $(object->string (+ 3 2))
> 
> 
> or this (5)
> 
>     \version "2.19.82"
>     \markup $"Hello"
> 
> 
> Why the behaviour of (1) and (2) ?
> 
> * * *
> 
> I tried to rewrite (1) and (2) with the hash mark instead of dollar (6):
> 
>     \version "2.19.82"
>     #(object->string (+ 3 2))
> 
> 
> and (7):
> 
>     \version "2.19.82"
>     #"Hello"
> 
> 
> This time, there is no output in the pdf file. Why this difference?
> 
> Thank you, g.
> 
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