To Philip McGrath, Hi again
I modified the clause
((id ...) (in-value* expr ...))
to the following in-values clause:
((id ...) (in-values expr))
where the expr is supposed to return as many values as ids.
I simplified the code such as to avoid syntax-parse,
because I do not (yet) understand all its powerful features.
I prefer writing code I can understand in all details.
😉 I should study on syntax-parse in due future 😉
(define-sequence-syntax in-values
(λ (stx)
(raise-syntax-error 'in-values
"can only be used in for forms" stx))
(λ (stx)
(syntax-case stx ()
(((id ...) (_ expr))
#'((id ...)
(:do-in
(((id ...) expr))
#t () #t () #t #f ()))))))
For example:
(for/first (((a b c) (in-values (values 2 + 3)))) (b a c)) ; -> 5
Thanks again, Jos
From: Philip McGrath
Sent: 04 May 2020 17:21
To: Jos Koot
Cc: us...@racket-lang.org
Subject: Re: [racket-users] multiple-value version of in-value
My package `adjutor` has a few variants of this, like `in-value*`:
https://docs.racket-lang.org/adjutor/Stable.html#(part._.Sequence_.Constructors)
They can all be used as first-class procedures, but that does involve a little
runtime overhead, so they use `define-sequence-syntax` to cooperate directly
with `for`-like forms when possible.
-Philip
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