Re: Having trouble understanding optional and variable amount of arguments

[Stefano Troncaro]

Thank you! I see that this is not an option then. Also, I now understand why I couldn't make the optional arguments work, since I always left them for last.

Do you know if it is possible to have a flexible amount of optional arguments that appear before the last mandatory one? Say, for example (define-music-function (arg1 args music) (number? ??? ly:music?) where arg1 and music are mandatory, and basically everything between arg1 and the next music _expression_ is compacted into a list and accessed as args in the body of the function. Not with that syntax necessarily, but something that allows for that kind of usage?

2018-02-28 20:45 GMT-03:00 Simon Albrecht <address@hidden>:

On 28.02.2018 23:54, Stefano Troncaro wrote:

I need a little help again. I'm struggling to understand how one would make a music function like \tempo, that accepts a variable number of arguments. I couldn't find its definition so I couldn't look for myself.

So far I know about making lambdas that take additional arguments and store the extras in a list, but this does not work in a music function (or if it works I don't know how to do it). And while I could make a lambda that then passes the arguments to a music function, then I can't use it with Lilypond syntax, so I'm forced to put the lambda and all it's arguments between parenthesis.

But \tempo doesn't require parenthesis, and the parser still understands what is part of the function and what not. How would one go about writing a function that behaves like this?

As has been said, \tempo isn’t a music function. However, you _can_ define functions with optional arguments; it’s mentioned in <http://lilypond.org/doc/v2.19/Documentation/extending/scheme-function-definitions>. The last optional argument has to be followed by a mandatory argument of different type, because that’s how the parser will recognise that optional arguments were skipped.

HTH, Simon