How do I keep track of index when using a higher order function? [duplicate]

Question

I'm new to Haskell and I was wondering how would I be able to keep track of the index when it comes to higher order classes I'm trying to build a function that takes a [a] list and a function (a->Int->b) which essentially would be f(ai, i) and returns list [b].

I thought of doing something like:

higherOrd :: [a]->(a->Int->b)->[b] higherOrd t f = [f x y | x <- t, y <- [1..length(t)]]

for example, if I do higherOrd (1,2..10) (+) I get:

[2,3,4,5,6,7,8,9,10,11,3,4,5,6,7,8,9,10,11,12,4,5,6,7,8,9,10,11,12,13,5,6,7,8,9,10,11,12,13,14,6,7,8,9,10,11,12,13,14,15,7,8,9,10,11,12,13,14,15,16,8,9,10,11,12,13,14,15,16,17,9,10,11,12,13,14,15,16,17,18,10,11,12,13,14,15,16,17,18,19,11,12,13,14,15,16,17,18,19,20]

when I would want to get [2,4,6,8,10,12,14,16,18,20]

willeM_ Van Onsem · Accepted Answer · 2023-03-24 17:14:22Z

You use zip:

higherOrd :: [a] -> (a -> Int -> b) -> [b] higherOrd t f = [f x y | (x,y) <- zip f [1..]]

this then enumerates over the two lists at the same time. Or we work with a function that Haskell already provides: zipWith:

higherOrd :: [a] -> (a -> Int -> b) -> [b] higherOrd t f = zipWith f t [1..]

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