Library function to compose a function with itself n times

Question

Is there a library function available in Haskell to compose a function with itself n times?

For example I have this function:

func :: a -> a

and I want to do this:

func . func . func . func . func . func , ... 

(up to n times, where n is only known at runtime).

Note that the iterate function would not be appropriate for what I am doing, since I do not care about any intermediate results.

Answer 1

\xs n -> iterate func xs !! n

I don't know why, but I feel like iterate is something people aren't consistently exposed to when learning Haskell.

If you don't like !! then you could use zip and lookup as an alternative. (some people/groups/tools don't like functions that call "error" in certain cases, I'm not claiming lookup is any better in these cases)

lookup n . zip [0..] . iterate func

EDIT: Ok, so I deleted then undeleted because I agree with the other answerer - you shouldn't discount use of iterate just because it gives you more than you need.

Answer 2

I do not know why you say that iterate is not appropriate. It is perfectly suitable for this purpose. (!! n) . iterate func is the composition of n copies of func.

(Someone had posted an answer similar to the above code, but he/she seems to have deleted it.)

Answer 3

The iterate solution is fine, or you might like this one: the composition of n copies of f is foldr (.) id (replicate n f).

Answer 4

(\n -> appEndo . mconcat . replicate n . Endo) n f x