Hi Andy!
Andy Wingo <[EMAIL PROTECTED]> writes:
> On Fri, 2007-05-25 at 20:12 +0200, Ludovic Courtès wrote:
>> Alas, it breaks the following test in `syntax.test':
>
> I'm not sure what "it" is in this case; I assume you mean the fix to
> module-make-local-var!.
"It" means "the reordering of `eval_car' and `sym2var' in `eval.c'".
>> (pass-if "binding is created before expression is evaluated"
>> (= (eval '(begin
>> (define foo
>> (begin
>> (set! foo 1)
>> (+ foo 1)))
>> foo)
>> (interaction-environment))
>> 2))
>>
>> This test case illustrates the fact that _internal_ defines are
>> equivalent to `letrec' (Section 5.2.2); top-level defines should behave
>> similarly for new variables (Section 5.2.1).
>
> I don't know what you are trying to say here; top-level defines do not
> "behave similarly" to letrec. R5RS says in section 5.2.1:
>
> If <variable> is not bound, however, then the definition will
> bind <variable> to a new location before performing the
> assignment, whereas it would be an error to perform a `set!' on
> an unbound variable.
>
> The new variable should be created before the assignment, but _not
> necessarily before evaluation of the rhs_.
Oh, right, there's a subtle difference here, so your interpretation may
well be valid, indeed.
> I think the test is bogus.
Actually, no: the test does a `define' _within_ the body of `begin', so
I *think* this qualifies as an internal define, and internal defines are
equivalent to `letrec' (Section 5.2.2). So the test is equivalent to:
(letrec ((foo (begin
(set! foo 1)
(+ foo 1))))
foo)
And this is valid (and does actually work in all the previously
mentioned implementations except SCM).
IOW, `scm_m_define ()' must be refined to distinguish between internal
defines and top-level defines.
Needs some more thought now...
Thanks!
Ludovic.
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