-- Computes the factorial of a number.
fac :: Integer -> Integer
fac n = if n == 0 then 1 else fac (n - 1) * n

---- Enumeration types

-- Boolean values:
-- data Bool = False | True

-- Color type:
data Color = Red | Blue | Yellow

aColor :: Color
aColor = Yellow

colorValue :: Color -> Int
colorValue Red    = 0
colorValue Blue   = 1
colorValue Yellow = 2

--- Record types: one constructor with arguments

-- Complex numbers
data Complex = Complex Float Float
  deriving Show

aC :: Complex
aC = Complex 1.5 2.4

-- Addition on complex numbers:
addC :: Complex -> Complex -> Complex
addC (Complex r1 i1) (Complex r2 i2) = Complex (r1 + r2) (i1 + i2)


--- Mixed data types

-- Integer lists:
data IntList = Nil | Cons Int IntList
 deriving Show

-- 1,2,3:
list123 :: IntList
list123 = Cons 1 (Cons 2 (Cons 3 Nil))

-- Concatenation of two integer lists:
append :: IntList -> IntList -> IntList
append Nil         ys = ys
append (Cons x xs) ys = Cons x (append xs ys)