CODEWITHSUNDEEP
functionhaskell
Bob Marley
Bob Marley

Reputation: 91

Haskell writing my own function to compose functions

so I am trying to write my own function to compose a function n times in Haskell.

so for example, the input

compose (+1) 3

would return f(x) = x+3;

Now my attempt is as follows, but is actually quite naive and currently doesn't work.

compose f 0 = (*1)
compose f n = (compose f n-1).a

Upvotes: 3

Views: 137

Answers (1)

Cactus
Cactus

Reputation: 27636

In the second case, you are trying to refer to a which I think you meant as f, since then

compose f n = (compose f (n-1)) . f

(note also that compose f n - 1 is parsed as (compose f n) - 1 in your code)

which means you have

compose f 3 = (compose (+1) 2)             . f
            = ((compose (+1) 1)       . f) . f
            = (((compose (+1) 0) . f) . f) . f
            = ((((*1)            . f) . f) . f

Oh and by the way, you can write

compose f 0 = id

which expresses the idea that compose f 0 should do "nothing".

Upvotes: 7

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