Hi jobol,

thank you for your reply!

jobol <xxxxxx@nonadev.net> writes:

> I'm suspecting that the example
>
> (define-typed (foo a) (integer? -> (all-integer?))
>   (values a a))
>
> should be
>
> (define-typed (foo a) (integer? -> all-integer?)
>   (values a a))

(all-integer?) is correct: it means that `all-integer?' receives all
values to check in one go.

The parentheses are required to distinguish it from single-value return.

This:

(define (all-integer? vals)
  (not (member #f (map integer? vals))))
(define-typed (foo a) (integer? -> (all-integer?))
  (values a a))

Does the same value checks as

(define-typed (foo a) (integer? -> (integer? integer?))
  (values a a))

But with more flexibility for the implementation (adding a third value
will still validate, because all-integer? doesn’t care about the number
of values).

The parentheses around (integer? integer?) are necessary to make this
easy to implement with syntax-rules (using an ellipsis two times at the
same depth causes problems).

For the single-return value there’s the special case without parentheses,
because that’s the most common, so it should have the least amount of
syntax overhead:

(define-typed (foo a) (integer? -> integer?) a)

Best wishes,
Arne
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