CODEWITHSUNDEEP
functionhaskellarguments
user2921302
user2921302

Reputation: 69

How do you use a function inside arguments in haskell?

I am on a problem that asked to write a function that applies a function to an Integer and calculate the answer. Here is the problem:

Declare the type and define a function that takes a function (say f) and an integer (say n) and returns f 0 + f 1 + f 2 + … + f n. For example, fun sq 5 would returns 55 which is 0+1+4+9+16+25 (“sq” means “square”).

Does anyone know how to do that? I would very much appreciate it.

Upvotes: 2

Views: 251

Answers (1)

daniel gratzer
daniel gratzer

Reputation: 53911

This is called a higher order function

fun :: (Int -> Int) -> Int -> Int
fun f n = ???

And we just use f like a normal function, writing f 0 or whatever. ??? is the haskell translation of

 f 0 + f 1 + ... + f n

As for how to do this, this looks like homework so I'll just hint you to look at using [0..n] to get a list from 0 to n and

map :: (Int -> Int) -> [Int] -> [Int] -- restricting for clarity

which applies a function to every item in a list (hey it's another higher order function)

sum :: [Int] -> Int

Which adds up all the numbers in a list.

Upvotes: 4

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