Maybe.hs

{-# OPTIONS_JHC -fno-prelude #-}
module Data.Maybe (
    Maybe(Nothing, Just),  maybe,  isJust,  isNothing,  fromJust,  fromMaybe,
    listToMaybe,  maybeToList,  catMaybes,  mapMaybe
    ) where

import Jhc.Maybe
import Jhc.Order
import Jhc.Basics
import Jhc.IO

isJust                 :: Maybe a -> Bool
isJust (Just a)        =  True
isJust Nothing         =  False

isNothing        :: Maybe a -> Bool
isNothing        =  not . isJust

fromJust               :: Maybe a -> a
fromJust (Just a)      =  a
fromJust Nothing       =  error "Maybe.fromJust: Nothing"

fromMaybe              :: a -> Maybe a -> a
fromMaybe d Nothing    =  d
fromMaybe d (Just a)   =  a

maybeToList            :: Maybe a -> [a]
maybeToList Nothing    =  []
maybeToList (Just a)   =  [a]

listToMaybe            :: [a] -> Maybe a
listToMaybe []         =  Nothing
listToMaybe (a:_)      =  Just a

catMaybes              :: [Maybe a] -> [a]
catMaybes ms           =  [ m | Just m <- ms ]

mapMaybe               :: (a -> Maybe b) -> [a] -> [b]
mapMaybe f             =  catMaybes . map f