CODEWITHSUNDEEP
listfunctionhaskellrecursionoptimization
codingbudgie
codingbudgie

Reputation: 327

Haskell recursively applying function to every element but first?

So I've been doing this program which receives a function f, a number a and a list b and it should return a list [a, f(a,b), f(f(a,b),b, ..] iterating through the list b and using recursion. Do you guys know how I can optimize my code?

calculate :: (a -> b -> a) -> a -> [b] -> [a]
help :: (a -> b -> a) -> a -> [b] -> [a]

help f a (x:xs) = (f a x) : (calculate f (f a x) xs)
help f a [] = []

calculate f a b = a : (help f a b)

Upvotes: 2

Views: 374

Answers (1)

Will Ness
Will Ness

Reputation: 71109

calculate f a b = tail . concatMap (replicate 2) . scanl f a $ b.

The replicate bit is probably in error. If so, then simply calculate = scanl.

This translates the code, as the "[a, f(a,b), f(f(a,b),b, ..]" from the text contradicts it (and it contradicts the text itself, which talks of "iterating through the list b").

Upvotes: 2

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