{-# LANGUAGE OverloadedStrings #-}
import           Data.String (IsString( .. ))

data Foo = Bar | Baz deriving (Eq, Show)

instance Num Foo where
  _ + _         = Bar
  _ * _         = Baz
  abs _         = Bar
  signum _      = Baz
  fromInteger 0 = Bar
  fromInteger 1 = Baz
  fromInteger _ = Bar
  negate Bar    = Baz
  negate Baz    = Bar

instance IsString Foo where
  fromString "bar" = Bar

x :: Foo
x = 0

y :: Foo
y = 1

z :: Foo
z = "bar"

example :: Foo -> Bool
example 0 = True
example _ = False

example2 :: Foo -> Bool
example2 "bar" = True
example2 _     = False

main :: IO ()
main = do
  print x -- Bar
  print y -- Baz
  print $ example Bar -- True
  
  print z -- Bar
  print $ example Baz -- False