Redo 14.6 and write some instances of the Arbitrary typeclass

Author: dwayne

ch14/qc/CoArbitrary.hs

@@ -0,0 +1,18 @@
+{-# LANGUAGE DeriveGeneric #-}
+
+module CoArbitrary where
+
+import GHC.Generics
+import Test.QuickCheck
+
+data Bool' = True' | False' deriving (Generic)
+
+instance CoArbitrary Bool'
+
+-- coarbitrary :: CoArbitrary a => a -> Gen b -> Gen b
+
+trueGen :: Gen Int
+trueGen = coarbitrary True' arbitrary
+
+falseGen :: Gen Int
+falseGen = coarbitrary False' arbitrary

ch14/qc/First.hs

@@ -0,0 +1,79 @@
+module First where
+
+-- 14.6 Kicking around QuickCheck
+
+import Test.QuickCheck
+
+data Trivial = Trivial deriving (Eq, Show)
+
+trivialGen :: Gen Trivial
+trivialGen = return Trivial
+
+instance Arbitrary Trivial where
+  arbitrary = trivialGen
+
+data Identity a = Identity a deriving (Eq, Show)
+
+identityGen :: Arbitrary a => Gen (Identity a)
+identityGen = arbitrary >>= return . Identity
+-- identityGen = do
+--   a <- arbitrary
+--   return (Identity a)
+
+instance Arbitrary a => Arbitrary (Identity a) where
+  arbitrary = identityGen
+
+identityGenInt :: Gen (Identity Int)
+identityGenInt = identityGen
+
+data Pair a b = Pair a b deriving (Eq, Show)
+
+pairGen :: (Arbitrary a, Arbitrary b) => Gen (Pair a b)
+pairGen = do
+  a <- arbitrary
+  b <- arbitrary
+  return (Pair a b)
+
+instance (Arbitrary a, Arbitrary b) => Arbitrary (Pair a b) where
+  arbitrary = pairGen
+
+pairGenIntString :: Gen (Pair Int String)
+pairGenIntString = pairGen
+
+data Sum a b = First a | Second b deriving (Eq, Show)
+
+-- equal Odds
+sumGenEqual :: (Arbitrary a, Arbitrary b) => Gen (Sum a b)
+sumGenEqual = do
+  a <- arbitrary
+  b <- arbitrary
+  oneof [ return $ First a
+        , return $ Second b
+        ]
+
+-- instance (Arbitrary a, Arbitrary b) => Arbitrary (Sum a b) where
+--   arbitrary = sumGenEqual
+
+sumGenCharInt :: Gen (Sum Char Int)
+sumGenCharInt = sumGenEqual
+
+-- from the QuickCheck library
+-- instance Arbitrary a => Arbitrary (Maybe a) where
+--   arbitrary = frequency [ (1, return Nothing)
+--                         , (3, liftM Just arbitrary)
+--                         ]
+
+sumGenFirstPls :: (Arbitrary a, Arbitrary b) => Gen (Sum a b)
+sumGenFirstPls = do
+  a <- arbitrary
+  b <- arbitrary
+  frequency [ (10, return $ First a)
+            , (1, return $ Second b)
+            ]
+
+sumGenCharIntFirst :: Gen (Sum Char Int)
+sumGenCharIntFirst = sumGenFirstPls
+
+main :: IO ()
+main = do
+  sample trivialGen

ch14/qc/qc.cabal

@@ -14,7 +14,9 @@ cabal-version:       >=1.10
 
 library
   hs-source-dirs:       .
-  exposed-modules:      Examples
+  exposed-modules:      CoArbitrary
+                      , Examples
+                      , First
   ghc-options:          -Wall -fwarn-tabs
   default-language:     Haskell2010
   build-depends:        base >= 4.7 && < 5