-- maybe.hs: conjuring functions over maybe values
--
-- Copyright (C) 2024 Rudy Matela
-- Distributed under the 3-Clause BSD licence (see the file LICENSE).
import Conjure
isNothing' :: Maybe A -> Bool
isNothing' Nothing = True
isNothing' (Just 0) = False
isNothing' (Just 1) = False
isJust' :: Maybe A -> Bool
isJust' Nothing = False
isJust' (Just 0) = True
isJust' (Just 1) = True
fromMaybe' :: A -> Maybe A -> A
fromMaybe' 0 Nothing = 0
fromMaybe' 1 Nothing = 1
fromMaybe' 0 (Just 1) = 1
fromMaybe' 1 (Just 2) = 2
maybeSpec :: (A -> (A -> A) -> Maybe A -> A) -> Bool
maybeSpec maybe = and
[ maybe 0 undefined Nothing == 0
, maybe 1 undefined Nothing == 1
, maybe undefined (+1) (Just 1) == 2
, maybe undefined (*2) (Just 3) == 6
]
listToMaybe' :: [A] -> Maybe A
listToMaybe' [] = Nothing
listToMaybe' [2] = Just 2
listToMaybe' [0,1] = Just 0
listToMaybe' [1,0] = Just 1
maybeToList' :: Maybe A -> [A]
maybeToList' Nothing = []
maybeToList' (Just 0) = [0]
maybeToList' (Just 1) = [1]
maybeToList' (Just 2) = [2]
catMaybes' :: [Maybe A] -> [A]
catMaybes' [] = []
catMaybes' [Nothing] = []
catMaybes' [Just x] = [x]
catMaybes' [Just x, Nothing, Just y] = [x,y]
main :: IO ()
main = do
conjure "isNothing" isNothing' primitives
conjure "isJust" isJust' primitives
conjure "fromMaybe" fromMaybe' primitives
conjureFromSpec "maybe" maybeSpec primitives
conjure "listToMaybe" listToMaybe' primitives
conjure "maybeToList" maybeToList' primitives
-- only top-level break downs, so would need morePrimitives
conjure "catMaybes" catMaybes' primitives
-- conjure "mapMaybe" mapMaybe' primitives -- same
primitives :: [Prim]
primitives =
[ pr (Nothing :: Maybe A)
, prim "Just" (Just :: A -> Maybe A)
, pr False
, pr True
, pr ([] :: [A])
, prim ":" ((:) :: A -> [A] -> [A])
]
{-
morePrimitives :: [Prim]
morePrimitives = primitives ++
[ prim "isNothing" (isNothing :: Maybe A -> Bool)
, prim "isJust" (isJust :: Maybe A -> Bool)
, prim "fromJust" (fromJust :: Maybe A -> A)
, prif (undefined :: A)
, prif (undefined :: Maybe A)
, prif (undefined :: [A])
]
-}