Hi,
Andy Wingo <wi...@pobox.com> skribis:
> Regarding identity, `cons' needs to return objects with identity. These
> expressions expressions are not the same:
>
> (define f
> (let ((pair (cons 1 2)))
> (lambda ()
> pair)))
>
> (define f
> (lambda ()
> (cons 1 2)))
>
> Here we cannot propagate `pair' because then we would break (eq? (f)
> (f)). It's a question of identity.
Right, good point.
[...]
> `car' is pure -- if its argument is
> indeed a pair, then it has no side effects -- but it is not constant.
OK, got it!
(Though I think that the term ‘constant’, as used by GCC, is confusing.
I don’t have a better name to propose, though.)
[...]
>>> Also, if I'm correct in guessing the reason for this change (accessing
>>> mutable memory), shouldn't the bytevector-*-ref operations go as well?
>>
>> No because they return an immutable object.
>
> I think we got this wrong, Ludo, and we should probably create some list
> of pure accessors for mutable data and put bytevector-*-ref in it, for
> the same reason given above for `h'.
Yes, agreed.
Thanks!
Ludo’.
PS: In that context, it must be quite a relief to work on a purely
functional language... :-)
