-- Peano representation of natural numbers:
data Nat = Z | S Nat
  deriving Show

-- Addition on natural numbers:
add :: Nat -> Nat -> Nat
add Z     n = n
add (S m) n = S (add m n)

-- A partial function:
f :: Nat -> Nat -> Nat
f (S m) n = Z

-- Not normalizing:  > add (add x Z) (add Z Z)
-- Not normalizing:  > f Z (add Z Z)

g :: Bool -> Bool -> Int
g False False = 0
g _     True  = 1

loop :: Bool
loop = loop

-- Haskell pattern matching does not compute the normal form of
--
-- > g loop True
--
-- (in contrast to strategy "phi")