l...@gnu.org (Ludovic Courtès) writes:
> R5RS defines ‘values’ as:
>
> (define (values . things)
> (call-with-current-continuation
> (lambda (cont) (apply cont things))))
>
> Thus, a conforming implementation must raise a run-time error when the
> continuation of a (values) form expects one or more values.
No. From R5RS:
-- procedure: call-with-current-continuation proc
[...]
The escape procedure accepts the same number of arguments as the
continuation to the original call to
call-with-current-continuation. Except for continuations created
by the `call-with-values' procedure, all continuations take
exactly one value. The effect of passing no value or more than
one value to continuations that were not created by
call-with-values is unspecified.
Please reread the last sentence. "unspecified". In fact, passing more
than one value to continuations that were not created by
call-with-values already does not raise a runtime error but instead just
drops the additional values:
(+ (values 4 5) 5) => 9
This patch _provides_ a default value when 0 values are given. That's
filling in a different unspecified behavior than throwing an error, but
Guile already fills in a different unspecified behavior than throwing an
error for multiple values.
So this behavior is neither out of line, nor against the standard. It
is merely a more convenient behavior for a situation that the standard
left unspecified.
--
David Kastrup
