Re: Behavior of #!optional

[Evan Hanson]

Hi Théo,

I don't know whether there are any firm guarantees about that behaviour,
but functionally it's safe to rely on, yes. That idiom you mentioned is
pretty handy, I use it myself sometimes.

Under the hood, #!optional arguments are expanded in a let*-style
binding form (as opposed to a "normal" let binding, where they wouldn't
see one another), so later values can refer to earlier ones.

Cheers,

Evan