Haskell #solo

import Data.List
import System.IO
import Data.Array

collatz n
     | mod n 2 == 0 = div n 2
     | otherwise =  3 * n + 1

collatzList n
        | n < 1 = error "Cannot have negative number"
        | n == 1 = [n]
        | otherwise = let sql = n:collatzList (collatz n)
        in sql

search :: [Int] -> Int -> Int
search (x:xs) y = if x == y then 1 else 1 + search xs y

length' :: (Num b) => [a] -> b
length' [] = 0
length' (_:xs) = 1 + length' xs

maximum' :: (Ord a) => [a] -> a
maximum' [] = error "maximum of empty list"
maximum' [x] = x
maximum' (x:xs)
    | x > maxTail = x
    | otherwise = maxTail
    where maxTail = maximum' xs

main :: IO ()
main = do
n <- getLine
print (search (map length' (map collatzList [1..(read n :: Int)])) (maximum' (map length' (map collatzList [1..(read n :: Int)]))))