-- Computes the n-th Fibonacci number
fib1 :: Int -> Int
fib1 n = if n == 0 then 0
                   else if n == 1 then 1
                                  else fib1 (n - 1) + fib1 (n - 2)

-- Computes the n-th Fibonacci number
fib2 :: Int -> Int
fib2 n = fib2iter 0 1 n

fib2iter :: Int -> Int -> Int -> Int
fib2iter fibn fibnp1 n = if n == 0 then fibn
                                   else fib2iter fibnp1 (fibn + fibnp1) (n - 1)

-- Computes the n-th Fibonacci number
fib3 :: Int -> Int
fib3 n = iter 0 1 n
 where iter :: Int -> Int -> Int -> Int
       iter fibn fibnp1 n = if n == 0 then fibn
                                      else iter fibnp1 (fibn + fibnp1) (n - 1)

-- Computes the n-th Fibonacci number
fib4 :: Int -> Int
fib4 n =
 let iter fibn fibnp1 n = if n == 0 then fibn
                                    else iter fibnp1 (fibn + fibnp1) (n - 1)
 in  iter 0 1 n

let1 = let x = 5
           y = 6
       in (x*y) + 12

let2 = (let x = 5
            y = 6
        in (x*y)) + 12

let3 = 12 + (let   x = 5
                   y = 6
             in (x*y))

let4 = 12 + (let { x = 5 ; y = 6 } in x*y)

-- Checks whether a number is prime
isPrim :: Int -> Bool
isPrim n = n /= 1 && noSmallerDiv (n `div` 2)
 where
  noSmallerDiv m = m == 1 || (mod n m /= 0 && noSmallerDiv (m - 1))