Re: Inconsistency with expressions between definitions

[Linus Björnstam]

Hey!

When you are not referencing x before defining y everything works as you 
want. There is no, so to say, temporal dependency on how the things are 
bound. When you introduce (display x) before actually defining y you 
force letrec* to bind x to the unspecified value, because display has 
side-effects and you don't move around side-effecting code.

If you do (display "heippa!") instead it works as you want.

I believe racket (which does the same optimization) has the same behaviour.

-- Linus Björnstam

Den 2023-09-24 kl. 09:09, skrev Dr. Arne Babenhauserheide:
> Hi,
>
> while writing a comment to SRFI-245 I think I found an inconsistency in
> the Implementation in Guile.
>
> This works:
>
> (define (using-later-variable)
>    (define x y)
>    (define y #t)
>    x)
> (using-later-variable)
> ;; => #t
>
> This still works:
>
> (define (using-later-variable)
>    (define x y)
>    (newline)
>    (define y #t)
>    x)
> (using-later-variable)
> ;; => (newline output)
> ;; => #t
>
> This fails:
>
> (define (using-later-variable)
>    (define x y)
>    (display x)
>    (newline)
>    (define y #t)
>    x)
> (using-later-variable)
> ;; => #<unspecified>
>
> Best wishes,
> Arne