fibs haskell

module Fib
    (
        simpleRecursionFibs,
        tailRecursionFibs,
        byZipWithFibs,
        simpleIterateFibs
    ) where

{-
    fibs by usual recursion
-}

simpleRecursionFibs :: Int -> [Integer]
simpleRecursionFibs n = map simpleRecursionFib [1 .. n]

simpleRecursionFib :: Int -> Integer
simpleRecursionFib 0 = 1
simpleRecursionFib 1 = 1
simpleRecursionFib n = simpleRecursionFib (n - 1) + simpleRecursionFib (n - 2)

{-
    fibs by tail recursion
-}

tailRecursionFibs :: Int -> [Integer]
tailRecursionFibs n = map tailRecursionFib [1 .. n]

fibsTailTriple :: (Int, Integer, Integer) -> Int -> (Int, Integer, Integer)
fibsTailTriple (curN, x, y) n =
    if curN < n
    then fibsTailTriple (curN + 1, y, x + y) n
    else (curN, x, y)

third :: (x,y,z) -> z
third (x,y,z) = z

tailRecursionFib :: Int -> Integer
tailRecursionFib n = third (fibsTailTriple (0,0,1) n)

{-
    by zipWith
-}

byZipWithFibs :: Int -> [Integer]
byZipWithFibs n = take n fibsByZipWith

fibsByZipWith = 1 : 2 : zipWith (+) fibsByZipWith (tail fibsByZipWith)

{-
    simple iterate fibs
-}

simpleIterateFibs :: Int -> [Integer]
simpleIterateFibs n = take n simpleIterateFib

simpleIterateFib = map fst (iterate f (1, 2)) where f (x, y) = (y, x + y)