-- Below, are four different ways to implement this infinite corecursive sequence:
-- https://en.wikipedia.org/wiki/Fibonacci_sequence

-- | if then else
-- >>> fibIf 10
-- 89
fibIf :: Int -> Int
fibIf x =
  if x == 1
    then 1
    else
      if x == 2
        then 2
        else fibIf (x - 1) + fibIf (x - 2)

-- | Guards
-- >>> fibGuard 10
-- 89
fibGuard :: Int -> Int
fibGuard x
  | x == 1 = 1
  | x == 2 = 2
  | otherwise = fibGuard (x - 1) + fibGuard (x - 2)

-- | Actual case
-- >>> fibCase 10
-- 89
fibCase :: Int -> Int
fibCase x = case x of
  1 -> 1
  2 -> 2
  x -> fibCase (x - 1) + fibCase (x - 2)

-- | Syntantic sugar for case
-- >>> fibOverload 10
-- 89
fibOverload :: Int -> Int
fibOverload 1 = 1
fibOverload 2 = 2
fibOverload x = fibOverload (x - 1) + fibOverload (x - 2)