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 ...)
      (((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
Subject: Re: [racket-users] multiple-value version of in-value

My package `adjutor` has a few variants of this, like `in-value*`:

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.


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