PureScript by Example - 4.15 Prefer Folds to Explicit Recursion - Exercise 1, 3, 4 Solutions

Folds.purs

module Folds where

import Prelude
import Data.Foldable
import Data.Array.Partial
import Partial.Unsafe

-- Exercise 1
allTrue :: Array Boolean -> Boolean
allTrue = foldl (&&) true

-- Exercise 3
count :: forall a. (a -> Boolean) -> Array a -> Int
count f arr = count' f arr 0
  where
    count' :: forall a. (a -> Boolean) -> Array a -> Int -> Int
    count' _ [] acc = acc
    count' f arr acc = count' f (unsafePartial tail arr) (acc + (if f (unsafePartial head arr) then 1 else 0))

-- Exercise 4
reverse :: forall a. Array a -> Array a
reverse = foldl (\arr elem -> [elem] <> arr) []