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{-# LANGUAGE DataKinds #-} | |
{-# LANGUAGE KindSignatures #-} | |
{-# LANGUAGE FlexibleInstances #-} | |
{-# LANGUAGE FlexibleContexts #-} | |
{-# LANGUAGE GADTs #-} | |
{-# LANGUAGE TypeFamilies #-} | |
{-# LANGUAGE TypeOperators #-} | |
{-# LANGUAGE PolyKinds #-} | |
{-# LANGUAGE RankNTypes #-} | |
module Singletons where | |
import Data.Kind (Type) | |
-- import GHC.TypeNats | |
canMakeMove :: Int -> Int -> Either [Char] Bool | |
canMakeMove n m | |
| n == m = Left "Can't call function w/ equal args!" | |
| n > m = Right True | |
| n < m = Right False | |
-- foo :: 5 | |
-- foo = undefined | |
foo2 :: (a :: Type) | |
foo2 = undefined | |
-- Singleton: | |
-- | |
-- | |
data Nat -- defines the "kind" Nat | |
= Zero -- defines the "type" Zero | |
| Succ Nat -- defines the "type" Succ Nat | |
data SNat (n :: Nat) where | |
SZero :: SNat 'Zero | |
SSucc :: SNat n -> SNat ('Succ n) | |
type family (:==:) (a :: k) (b :: k) where | |
x :==: x = 'True | |
x :==: y = 'False | |
f :: SNat 'Zero | |
f = SZero | |
instance Eq (SNat 'Zero) where | |
SZero /= SZero = False | |
instance Eq (SNat n) => Eq (SNat ('Succ n)) where | |
SSucc n /= SZero = True | |
SSucc n /= SSucc m = n /= m | |
sCanMakeMove :: ((n :==: m) ~ 'False) => SNat n -> SNat m -> Bool | |
sCanMakeMove n m = True |
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