4.1. Examples

prefix_2 :: Eq a => [a] -> [a] -> [a]

prefix_2 xs [] = []
prefix_2 [] xs = []
prefix_2 (a:as) (b:bs) = if a == b
                         then a:(prefix_2 as bs)
                         else []

-- Can also be expressed as:
prefix_2_other xs ys = map fst . takeWhile (uncurry (==)) $ (zip xs ys)

gc_prefix :: Eq a => [[a]] -> [a]

gc_prefix [] = []
gc_prefix (a:as) = foldl prefix_2 a as

import List

mysplit :: Eq a => [a] -> [a] -> [[a]]

mysplit separator base = helper base where
    len = (length separator)
    helper [] = [[]]
    helper base =
        (if (isPrefixOf separator base)
         then []:(helper (drop len base))
         else let ret = (helper (tail base))
              in (head(base):head(ret)) : tail(ret)
        )