Traditional looping in Elm

Loop.elm

module Loop exposing (forEach)

loop : List a -> List b -> (a -> Int -> b) -> List b
loop a b fn =
    case a of
        [] ->
            b
        x::xs ->
            loop xs (b ++ [(fn x (List.length b))]) fn


forEach : List a -> (a -> Int -> b) -> List b
forEach a fn =
    loop a [] fn

-- Example Usage:
-- forEach [4,7,2,5] (\e i -> (i, e))
-- Output:
-- [(0,4),(1,7),(2,2),(3,5)]