ant.hs

module Ant where

import Data.List

group' :: [Int] -> [[Int]]
group' [] = []
group' xs = foldr (\x acc -> if (head . head) acc == x then (x : (head acc)) : tail acc else [x]:acc) [[last xs]] (init xs)

concatMap' :: (a -> [b]) -> [a] -> [b]
concatMap' f xs = (concat . map f) xs

ant = iterate (concatMap (\g -> [head g, length g]) . group) [1]
ant2 = iterate (concatMap' (\g -> [head g, length g]) . group') [1]

group.hs

-- | The 'group' function takes a list and returns a list of lists such
-- that the concatenation of the result is equal to the argument.  Moreover,
-- each sublist in the result contains only equal elements.  For example,
--
-- > group "Mississippi" = ["M","i","ss","i","ss","i","pp","i"]
--
-- It is a special case of 'groupBy', which allows the programmer to supply
-- their own equality test.
group                   :: Eq a => [a] -> [[a]]
group                   =  groupBy (==)

-- | The 'groupBy' function is the non-overloaded version of 'group'.
groupBy                 :: (a -> a -> Bool) -> [a] -> [[a]]
groupBy _  []           =  []
groupBy eq (x:xs)       =  (x:ys) : groupBy eq zs
                           where (ys,zs) = span (eq x) xs