elm/exercises/strain/Strain.example.elm

module Strain exposing (..)

import List


keep : (a -> Bool) -> List a -> List a
keep predicate list =
    List.foldr (consIf predicate) [] list


discard : (a -> Bool) -> List a -> List a
discard predicate list =
    List.foldr (consIf (\v -> not <| predicate v)) [] list


consIf : (a -> Bool) -> a -> List a -> List a
consIf predicate value list =
    if predicate value then
        value :: list
    else
        list