[Haskell-cafe] General function to count list elements?
lennart at augustsson.net
Sun Apr 19 19:25:07 EDT 2009
Sorry, I meant StableName.
On Mon, Apr 20, 2009 at 1:00 AM, Peter Verswyvelen <bugfact at gmail.com> wrote:
> Or a StableName? I guess StablePtr prevents the GC to move the Haskell
> object, so for just doing ugly comparing StableName would be better?
> On Mon, Apr 20, 2009 at 12:45 AM, Lennart Augustsson
> <lennart at augustsson.net> wrote:
>> And when the need gets big enough you pull out StablePtr and use that. :)
>> On Sun, Apr 19, 2009 at 10:43 PM, Peter Verswyvelen <bugfact at gmail.com>
>> > Sometimes I do miss the pragmatic C solution:
>> > - two function pointers that are equal surely represent the same
>> > functions
>> > (although in C nothing is really sure ;)
>> > - two function pointers that are different, might or might not represent
>> > that same functions.
>> > But this weak equality can sometimes be handy.
>> > For example, suppose you have a predicate a -> Bool, and a list of these
>> > predicates [a -> Bool], but you want to remove all functions that are
>> > obviously equal in the C way from the list for optimization... Okay big
>> > hack, and one could do this already with reallyUnsafePtrEquality# I
>> > guess...
>> > On Sat, Apr 18, 2009 at 6:02 PM, John A. De Goes <john at n-brain.net>
>> > wrote:
>> >> Two functions are equal iff they have the same domain and range and the
>> >> same outputs for the same inputs. Simple to state, but extremely
>> >> difficult
>> >> to implement in a useful way, and impossible to implement in a perfect
>> >> way.
>> >> If you had a compiler or algorithm capable of determining function
>> >> equality, you could use it to prove or disprove arbitrary theorems in
>> >> mathematics.
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