Re: Self-evaluating function and closure

[Mark H Weaver <mhw@netris.org>]

Hi Thomas,

Thomas Morley <thomasmorley65@gmail.com> writes:

> always interested in guile developments with regard to lilypond I
> noticed some inconsistence with my local lilypond-using-guile-2.9.2
> installation.
> I think I could break it down to pure guile (no lilypond)
>
> (1) The already stated behaviour:
> ~$ guile
> GNU Guile 2.9.2
> Copyright (C) 1995-2019 Free Software Foundation, Inc.
>
> Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'.
> This program is free software, and you are welcome to redistribute it
> under certain conditions; type `,show c' for details.
>
> Enter `,help' for help.
> scheme@(guile-user)> (define (function-generator)
>                       (let ((func #f))
>                         (lambda () (set! func (let a () a)) func)))
> scheme@(guile-user)> (define x (function-generator))
> scheme@(guile-user)> (define y (function-generator))
> scheme@(guile-user)> (write (version))
> "2.9.2"
> scheme@(guile-user)> (format #t "\nTEST: ~a" (eq? (x) (y)))
>
> TEST: #t
> $1 = #t
>
> (2) Doing it in a .scm-file (attached)
> ~$ guile --no-auto-compile eq-tst.scm
> "2.9.2"
> TEST: #f
>
> Did I something wrong or is it a bug?

Neither.  This is a case of unspecified behavior, and the behavior of
our compiler differs from that of our interpreter.  You will notice
similar discrepancies when comparing two literal lists or strings, where
our compiler will aggressively unify literals within a compilation unit,
and our interpreter does not:

--8<---------------cut here---------------start------------->8---
GNU Guile 2.2.4
Copyright (C) 1995-2017 Free Software Foundation, Inc.

Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'.
This program is free software, and you are welcome to redistribute it
under certain conditions; type `,show c' for details.

Enter `,help' for help.
scheme@(guile-user)> (eqv? "hello" "hello")
$1 = #t
scheme@(guile-user)> ,o interp #t
scheme@(guile-user)> (eqv? "hello" "hello")
$2 = #f
scheme@(guile-user)>
--8<---------------cut here---------------end--------------->8---

     Regards,
       Mark