CODEWITHSUNDEEP
listfunctionhaskell
GlossMash
GlossMash

Reputation: 89

Apply a function to next two elements in list

I am writing a function to apply a function for next two elements in list.

For example: applyToTwo (+) [1,2,3,4] return [3,5,7].

applyToTwo (-) [7,1,1,1,1] return [6,0,0,0].

I want to generalize the type so it could apply to any type I want. My attempt is:

applyToTwo :: (a -> a -> b) -> [a] -> [a]
applyToTwo f [] = []
applyToTwo f [x] = []
applyToTwo f (x:x1:rest) = f x x1 ++ applyToTwo f (x1:rest)

By the way, are there any way to generalize the number of element to apply so it could apply to 3, 4, 5?

Upvotes: 1

Views: 81

Answers (2)

Frerich Raabe
Frerich Raabe

Reputation: 94329

It appears you are simply zipping a list with its tail, so you could use zipWith:

applyToTwo f xs = zipWith f xs (tail xs)

Upvotes: 8

chi
chi

Reputation: 116139

This should do:

applyToTwo :: (a -> a -> b) -> [a] -> [b]
applyToTwo f [] = []
applyToTwo f [x] = []
applyToTwo f (x:x1:rest) = f x x1 : applyToTwo f (x1:rest)

Generalizing to arbitrary arities should be possible, but it requires some advanced type-level hackery.

Upvotes: 2

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