[Haskell-beginners] Does this function already exist in one of the standard modules?

[I. J. Kennedy]

I'm surprised there's no standard function for this.
Using   iterate f x !! n   is ok I suppose, but:

If I try to calculate the millionth fibonacci number like this

  fibStep (a,b) = (b,a+b)
  iterate fibStep (0,1) !! 1000000

I get a stack overflow, but if I use applyMany

  applyMany 1000000 fibStep (0,1)

it works.





On Sat, Aug 8, 2009 at 3:38 PM, Felipe Lessa<felipe.lessa at gmail.com> wrote:
> On Sat, Aug 08, 2009 at 03:01:34PM -0500, I. J. Kennedy wrote:
>> Does this function already exist in one of the standard modules?
>> It computes  f(f(f(...f(x))).  I suspect it is a common function, but I
>> can't find it, even using Hoogle.
>>
>>   applyMany :: Int -> (a -> a) -> a -> a
>>   applyMany 0 f x = x
>>   applyMany n f x = applyMany (n-1) f (f x)
>
> applyMany n f x = iterate f x !! n
>
> --
> Felipe.
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