What is the way to call optional functions as arguments?

[ofeeg]

For example, in guile-scheme you can do something like this:
(define* (what num #:optional (func list)) (func num))
I don't really know where to find this in the book. I searched around, but found nothing. I know the book is a WIP, so I figured I'd ask here before reading the entire thing.

[mattwparas]

This form is supported on the normal define, so just drop the * and you're good:

(define (what num #:optional (func list)) (func num))

(what 10) ;; => '(10)

[ofeeg]

That's weird... Earlier the playground was throwing a weird error. Unfortunately, I can't seem to get it to replicate the error and don't remember what it was. Thank you!