Add tour-example

examples/generic-random-examples.cabal

@@ -25,3 +25,15 @@ executable text-example
     text,
     generic-random
   default-language: Haskell2010
+
+executable tour-example
+  main-is: tour.hs
+  ghc-options: -Wall
+  if impl(ghc < 7.10)
+    ghc-options: -fcontext-stack=30
+  build-depends:
+    base,
+    QuickCheck,
+    text,
+    generic-random
+  default-language: Haskell2010

examples/tour.hs

@@ -0,0 +1,45 @@
+-- Just another toy example
+
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE InstanceSigs #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE TypeApplications #-}
+
+import Control.Monad
+import GHC.Generics
+import Test.QuickCheck
+
+import Generic.Random
+
+data MyType
+  = OneThing Int
+  | TwoThings Double String
+  | ThreeThings (Maybe Integer) [()] (Bool -> Word)
+  deriving (Show, Generic)
+
+custom :: GenList '[Maybe Integer]
+custom = (Just <$> arbitrary) :@ Nil
+
+instance Arbitrary MyType where
+  arbitrary :: Gen MyType
+  arbitrary = genericArbitraryG custom (1 % 4 % 4 % ())
+  -- arbitrary = frequency
+  --   [ (1, OneThing <$> arbitrary)
+  --   , (4, TwoThings <$> arbitrary <*> arbitrary)
+  --   , (4, ThreeThings <$> (Just <$> arbitrary) <*> arbitrary <*> arbitrary)
+  --   ]
+
+main = do
+  -- Print some examples
+  sample (arbitrary @MyType)
+
+  -- Check the property that ThreeThings contains three things.
+  quickCheck $ \case
+    ThreeThings Nothing _ _ -> False
+    _ -> True
+
+-- Ew. Sorry.
+instance Show a => Show (Bool -> a) where
+  show f = "<True -> " ++ show (f True) ++ ",False -> " ++ show (f False) ++ ">"