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))

Le Fri, 18 Sep 2026 17:13:42 -0700,
"Arthur A. Gleckler" <xxxxxx@speechcode.com> a écrit :

> Scheme Request for Implementation 284,
> "define-typed",
> by Arne Babenhauserheide,
> is now available for discussion.
>
> Its draft and an archive of the ongoing discussion are available at
> https://srfi.schemers.org/srfi-284/.
>
> You can join the discussion of the draft by filling out the
> subscription form on that page.
>
> You can contribute a message to the discussion by sending it to
> xxxxxx@srfi.schemers.org.
>
> Here's the abstract:
>
> This SRFI defines the forms define-typed and define-typed* for
> creating procedures with checked type boundaries. It allows checking
> the arguments and/or the return value or values with simple predicate
> procedures and raises exceptions on usage when they don't match. The
> form define-typed* supports keyword and optional arguments. The
> implementation for Guile is optimized to allow the compiler to use
> the predicates as guarantees to create more optimized code and
> provides type information for runtime introspection that supports
> SRFI 283.
>
> Regards,
>
> SRFI Editor