OnOdds.hs

import Data.List

onOdds :: ([a] -> [a]) -> [a] -> [a]
onOdds f xs =
    let
        (odds, evens) = partition (odd . fst) $ zip [0..] xs
    in
        concat $
            zipWith
                (\a b -> [a, b])
                (snd <$> evens)
                (f $ snd <$> odds)