1 files changed, 89 insertions, 0 deletions
diff --git a/Haskell-book/16/func/src/Func.hs b/Haskell-book/16/func/src/Func.hs
new file mode 100644
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+++ b/Haskell-book/16/func/src/Func.hs
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+module Func where
+
+import Test.QuickCheck
+
+-- class Functor f where
+--     fmap :: (a -> b) -> f a -> f b
+
+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 = fmap Identity arbitrary
+
+data Pair a = Pair a a deriving (Eq, Show)
+
+instance Functor Pair where
+    fmap f (Pair x y) = Pair (f x) (f y)
+
+instance Arbitrary a => Arbitrary (Pair a) where
+    arbitrary = do
+        x <- arbitrary
+        y <- arbitrary
+        return $ Pair x y
+
+data Two a b = Two a b deriving (Eq, Show)
+
+instance Functor (Two a) where
+    fmap f (Two x y) = Two x (f y)
+
+instance (Arbitrary a, Arbitrary b) => Arbitrary (Two a b) where
+    arbitrary = do
+        x <- arbitrary
+        y <- arbitrary
+        return $ Two x y
+
+data Three a b c = Three a b c deriving (Eq, Show)
+
+instance Functor (Three a b) where
+    fmap f (Three x y z) = Three x y (f z)
+
+instance (Arbitrary a, Arbitrary b, Arbitrary c) => Arbitrary (Three a b c) where
+    arbitrary = do
+        x <- arbitrary
+        y <- arbitrary
+        z <- arbitrary
+        return $ Three x y z
+
+data Three' a b = Three' a b b deriving (Eq, Show)
+
+instance Functor (Three' a) where
+    fmap f (Three' x y z) = Three' x (f y) (f z)
+
+instance (Arbitrary a, Arbitrary b) => Arbitrary (Three' a b) where
+    arbitrary = do
+        x <- arbitrary
+        y <- arbitrary
+        z <- arbitrary
+        return $ Three' x y z
+
+data Four a b c d = Four a b c d deriving (Eq, Show)
+
+instance Functor (Four a b c) where
+    fmap f (Four x y z t) = Four x y z (f t)
+
+instance (Arbitrary a, Arbitrary b, Arbitrary c, Arbitrary d)
+  => Arbitrary (Four a b c d) where
+      arbitrary = do
+        x <- arbitrary
+        y <- arbitrary
+        z <- arbitrary
+        t <- arbitrary
+        return $ Four x y z t
+
+data Four' a b = Four' a a a b deriving (Eq, Show)
+
+instance Functor (Four' a) where
+    fmap f (Four' x y z t) = Four' x y z (f t)
+
+instance (Arbitrary a, Arbitrary b) => Arbitrary (Four' a b) where
+      arbitrary = do
+        x <- arbitrary
+        y <- arbitrary
+        z <- arbitrary
+        t <- arbitrary
+        return $ Four' x y z t
+
+data Trivial = Trivial