Type level boolean values

Main.purs

module Main where

import Prelude (Unit)
import Control.Monad.Eff (Eff)
import Control.Monad.Eff.Console (CONSOLE, log)
import Data.Symbol (SProxy(SProxy), reflectSymbol)

data True
data False

class Show a (b :: Symbol) | a -> b
instance showTrue :: Show True "True"
instance showFalse :: Show False "False"

class Not a b | a -> b
instance notTrue :: Not True False
instance notFalse :: Not False True

class Xor a b c | a b -> c
instance xorTT :: Xor True True False
instance xorFT :: Xor False True True
instance xorTF :: Xor True False True
instance xorFF :: Xor False False False

foo :: forall a. Show True a => SProxy a
foo = SProxy

bar :: forall a b. (Not True a, Show a b) => SProxy b
bar = SProxy

xor :: forall a b c. (Xor True False a, Not a b, Show b c) => SProxy c
xor = SProxy

main :: forall e. Eff (console :: CONSOLE | e) Unit
main = log (reflectSymbol xor)