[Haskell-cafe] least fixed points above something

[Neil Mitchell]

CSE is tricky and a potential space leak in general. I'd love it if
the compiler could pick the best option, but I'm afraid its unlikely
to know.

On Thu, Mar 19, 2009 at 4:25 PM, Edsko de Vries <devriese at cs.tcd.ie> wrote:
> I always feel that the compiler should do such optimizations for me :)
> On 19 Mar 2009, at 16:21, Neil Mitchell wrote:
>
>>> I've used a similar function myself, but why write it in such a
>>> complicated
>>> way? How about
>>>
>>> lfp :: Eq a => (a -> a) -> a -> a
>>> lfp f x
>>>  | f x == x = x
>>>  | otherwise = lfp f (f x)
>>
>> I've used a similar function too, but your version computes f x twice
>> per iteration, I wrote mine as:
>>
>> fix :: Eq a => (a -> a) -> a -> a
>> fix f x = if x == x2 then x else fix f x2
>>   where x2 = f x
>>
>> I find this fix much more useful than the standard fix.
>>
>> Thanks
>>
>> Neil
>
>