Collatz.hs

module Collatz where

collatz :: (Integral a) => a -> [a]
collatz a = takeWhileIncl (/= 1) $ collatzSeq a

nextCollatz :: (Integral a) => a -> a
nextCollatz n = if (even n) then n `div` 2 else (3 * n + 1)

collatzSeq :: (Integral a) => a -> [a]
collatzSeq = iterate nextCollatz

takeWhileIncl :: (a -> Bool) -> [a] -> [a]
takeWhileIncl _ [] = []
takeWhileIncl p xs = left ++ [head right]
                     where (left, right) = span p xs