Forgot mailinglist, sorry. ---------- Forwarded message --------- From: Kees van den Doel <kvd...@gmail.com> Date: Wed, Aug 11, 2021 at 12:03 PM Subject: Re: 5.6.1 Substitution function syntax To: Jean Abou Samra <j...@abou-samra.fr>
Thanks Jean, David, That clarifies it, subtle stuff! Kees On Wed, Aug 11, 2021 at 11:45 AM Jean Abou Samra <j...@abou-samra.fr> wrote: > > > Le 11/08/2021 à 20:24, David Kastrup a écrit : > > Kees van den Doel <kvd...@gmail.com> writes: > > > >> Referring to > >> > https://lilypond.org/doc/v2.22/Documentation/notation/substitution-function-syntax > >> > >> I don't understand this sentence explanating "...music...": > >> > >>> normal LilyPond input, using $ (in places where only LilyPond > constructs > >> are allowed) or # (to use it as a Scheme value or music function > argument > >> or music inside of music >lists) to reference arguments (eg. ‘#arg1’). > >> > >> The next section in the docs with examples has no example of use of '$'. > >> When should I use $? > > In a nutshell, when # does not work. The syntax of an expression is > > decided before even looking at the value of the expression after # . So > > # in a certain place will only accept a certain type. > > > > For example, inside of { }, an expression started with # has to be a > > music expression, while $ allows expressions of type duration, pitch, > > post-event and probably others, integrating/converting them in the > > expected manner to music. > > > > $ first looks at the expression's type and then decides about its > > syntactic properties. Since the LilyPond expression parser works with > > lookahead for disambiguating expressions, that means that such > > expressions may be evaluated earlier than expected by the user. > > > > So generally # causes fewer syntactic surprises but is less flexible. > > Also it does not copy music expressions but takes them as-is. That can > > cause a difference in some cases. > > > Some examples are found in > > > https://extending-lilypond.readthedocs.io/en/latest/lily-and-scheme.html#hash-vs-dollar >
