Purescript Monoid Action exercise

gistfile1.purs

module Data.Action where

import Data.Array
import Data.Monoid

class (Monoid m) <= Action m a where
  act :: m -> a -> a

instance numberSemigroup :: Semigroup Number where
  (<>) x y = x * y

instance numberMonoid :: Monoid Number where
  mempty = 1

instance repeatAction :: Action Number String where
  act 0 _ = ""
  act n s = s ++ act (n - 1) s

instance arrayAction :: (Monoid m, Action m a) => Action m [a] where
  act x ys = go x ys
    where
    go _ [] = []
    go x (z : zs) = (act x z) : (go x zs)