Hi Cédric,
ri...@happyleptic.org skribis:
> Is it normal that this:
>
> (or (values 'a 'b) 'c)
>
> returns two values ('a and 'b)
This one gets optimized by peval:
scheme@(guile-user)> ,optimize (or (values 1 2) 'b)
$6 = (values 1 2)
That the second value isn’t truncated is a bug (see below.)
> while this:
>
> (or (values 'a (lambda (port) #f)) 'c)
>
> returns only one ('a)?
This one doesn’t:
scheme@(guile-user)> ,optimize (or (values 1 (lambda () #t)) 'b)
$5 = (begin
(letrec*
()
(let ((#{t 1263}# (values 1 (lambda () #t))))
(if #{t 1263}# #{t 1263}# 'b))))
The ‘let’, which leads to the second value being ignored, comes from the
definition of ‘or’:
(define-syntax or
(syntax-rules ()
((_) #f)
((_ x) x)
((_ x y ...) (let ((t x)) (if t t (or y ...))))))
It’s normal that the second value is ignored because ‘or’ expects
expressions returning one value.
In theory, peval should really optimize the first form to 1, instead of
multiple-values, but I think it loses information about the context
somewhere.
Namely, when partial-evaluating <let> forms, I think it should:
(let* ((vars (map (compose truncate lookup-var) gensyms))
...)
...)
where ‘truncate’ discards all values but the first of a <let-values>
form.
Andy?
Thanks,
Ludo’.
