FunctorInstances.hs

module FunctorInstances where

import           Test.QuickCheck

newtype Identity a = Identity a
    deriving (Eq, Show)

instance Functor Identity where
    fmap f (Identity a) = Identity (f a)

instance Arbitrary a => Arbitrary (Identity a) where
    arbitrary = Identity <$> arbitrary

data Pair a = Pair a a
    deriving (Eq, Show)

instance Functor Pair where
    fmap f (Pair a b) = Pair (f a) (f b)

instance (Arbitrary a) => Arbitrary (Pair a) where
    arbitrary = do
        a <- arbitrary
        Pair a <$> arbitrary

data Two a b = Two a b
    deriving (Eq, Show)

instance Functor (Two a) where
    fmap f (Two a b) = Two a (f b)

instance (Arbitrary a, Arbitrary b) => Arbitrary (Two a b) where
    arbitrary = do
        a <- arbitrary
        Two a <$> arbitrary

data Three a b c = Three a b c
    deriving (Eq, Show)

instance Functor (Three a b) where
    fmap f (Three a b c) = Three a b (f c)

instance (Arbitrary a, Arbitrary b, Arbitrary c) => Arbitrary (Three a b c) where
    arbitrary = Three <$> arbitrary <*> arbitrary <*> arbitrary

data Three' a b = Three' a b b
    deriving (Eq, Show)

instance Functor (Three' a) where
    fmap f (Three' a b b') = Three' a (f b) (f b')

instance (Arbitrary a, Arbitrary b) => Arbitrary (Three' a b) where
    arbitrary = Three' <$> arbitrary <*> arbitrary <*> arbitrary

data Four a b c d = Four a b c d
    deriving (Eq, Show)

instance Functor (Four a b c) where
    fmap f (Four a b c d) = Four a b c (f d)

instance (Arbitrary a, Arbitrary b, Arbitrary c, Arbitrary d) => Arbitrary (Four a b c d) where
    arbitrary = Four <$> arbitrary <*> arbitrary <*> arbitrary <*> arbitrary

data Four' a b c = Four' a b c c
    deriving (Eq, Show)

instance Functor (Four' a b) where
    fmap f (Four' a b c c') = Four' a b (f c) (f c')

instance (Arbitrary a, Arbitrary b, Arbitrary c) => Arbitrary (Four' a b c) where
    arbitrary = Four' <$> arbitrary <*> arbitrary <*> arbitrary <*> arbitrary