On 4/25/10 11:51 AM, "Mark Polesky" <markpole...@yahoo.com> wrote:
> Nicolas Sceaux wrote:
>> Inside the #{ ... #} construct, you have to use #$variable
>> where a scheme token is required, but you use $variable
>> where \variable could be used. Behind the scenes,
>> $variable is actually replaced by something like \tmpvar
>> before being parsed.
>
> Can you provide an example of a case where #$ is required
> within #{ #} ? I can't find one. $ seems to always work.
As I understand it, in LilyPond input, the # is a token that indicates a
Scheme expression follows.
In a #{ #} expression, $ is a token that indicates a Scheme expression to be
evaluated follows.
I don't think that #$ is ever required inside of #{ #}.
And there are some places where we use # that it is not strictly required,
i.e. where the argument needs to be a string, and it can be either a
LilyPond string (no #) or a Scheme string (start with a #).
We made a decision a number of years ago to always put # in if it was
accepted, even when it wasn't required, in order to be more consistent.
Similarly, we made a decision to put { after \new Staff, even if it wasn't
required, for consistency. So we do
\new Staff {
\new Voice {
c d e f
}
}
even though
\new Staff \new Voice {
c d e f
}
would also work.
In my opinion, we should not request that the user use #$, but we should
just indicate that inside a #{ #} block $ is used to indicate a Scheme
expression to be evaluated.
>
> In fact, I'm probably missing something obvious, but I'm
> unable even to find a case where a scheme token (with #) is
> actually required in a regular music block. I've found I
> can even do such bizarre things as this:
>
> voiceCtx = Voice
> noteGrob = NoteHead
> colorSym = #'color
> redVal = #red
>
> { \override \voiceCtx.\noteGrob \colorSym = \redVal c'' }
>
> and by extension, I can also do this (without using `#$'):
>
> overrideAlias =
> #(define-music-function
> (parser location ctx grob prop-sym prop-val)
> (scheme? scheme? scheme? scheme?)
> #{
> \override $ctx . $grob $prop-sym = $prop-val
> #})
>
> { \overrideAlias Voice NoteHead #'color #red c'' }
>
> So, two things:
> 1) what is a case where omitting the # causes an error?
I doubt there is one -- see above.
> 2) what is the danger of omitting the # otherwise?
I don't think there is any.
Carl
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