Placeholder

gistfile1.hs

import Data.List (elemIndex) 

tests :: (Int -> String -> String) -> [Bool]
tests wrap 
  = [ wrap 1 ""   == ""
    , wrap 1 "x"  == "x" 
    , wrap 1 "xx" == "x\nx" 
    , wrap 1 "xxx" == "x\nx\nx" 
    , wrap 1 "x x" == "x\nx"
    , wrap 2 "x x" == "x\nx"
    , wrap 3 "x xxxx" == "x\nxxx\nx"
    ]

check = putStrLn
      $ unlines
      $ zipWith (\n t -> show n ++ " " ++ if t then "ok" else "not") [1..] 
      $ tests wrap

--------------------

wrap_1 n x = x
wrap_2 n x = x

--------------------

wrap_3 n x | length x > n = take n x ++ "\n" ++ drop n x
           | otherwise    = x

--------------------

wrap_4 n x | length x > n = take n x ++ "\n" ++ wrap_4 n (drop n x)
           | otherwise    = x

--------------------

-- painful bit here
-- 
-- eg abc def x|  -> ("x", " fed cba")
-- eg abcdefx|  -> ("xfedcba", "") 
-- x, ' ' .... 

-- what about size zero? or negative? - but 0 is infinite.... 

wrap_5a n (' ':x) = wrap_5a n x
wrap_5a n x | null rest = line 
            | otherwise = reverse tail ++ "\n" ++ wrap_5a n (reverse head ++ rest)
  where (line,rest) = splitAt n x
        (tail, head) = break (== ' ') $ reverse line 

-- 5a probably not enough to distinguish "x x x "
-- blows on wrap_5 3 "x x x "
-- 5b does it ok 



-- maybe try refactoring? 
-- poss this is 5a with the null case inlined? 
-- benefits of equational reasoning
wrap_5b n x | null rest = line 
            | head rest == ' ' = line ++ "\n" ++ wrap_5b n (tail rest) 
            | null before      = line ++ "\n" ++ wrap_5b n rest
            | null after       = reverse (drop 1 before) ++ "\n" ++ wrap_5b n rest  
            | otherwise        = reverse before ++ "\n" ++ wrap_5b n (reverse after ++ rest)
  where (line,rest) = splitAt n x
        (after, before) = break (== ' ') $ reverse line 



--------------------

wrap_6 n (' ':x) = wrap_6 n x
wrap_6 n x | null rest = line 
           | null tail = reverse (drop 1 head) ++ "\n" ++ wrap_6 n rest
           | otherwise = reverse tail ++ "\n" ++ wrap_6 n (reverse head ++ rest)
  where (line,rest) = splitAt n x
        (tail, head) = break (== ' ') $ reverse line 

-- 5b not on 2 "x x"
-- problem on << wrap 3 "x xxxx" >>

--------------------
-- wrap 3 "x xxxx" - bad

wrap_7 n "" = ""
wrap_7 n (' ':x) = wrap_7 n x
wrap_7 n x | null rest = line 
           | otherwise = case break (== ' ') $ reverse line of 
                           (tail,     [])   -> reverse tail ++ "\n" ++ wrap_7 n rest
                           (tail, ' ':head) -> reverse head ++ "\n" ++ wrap_7 n (reverse tail ++ rest)
                           -- ([],       head) -> reverse head ++ "\n" ++ wrap_7 n rest
  where (line,rest) = splitAt n x

-- 5b not on 2 "x x"
wrap = wrap_7