--- a/7-Haskell/day2.hs	Mon Jun 17 20:50:43 2019 +0100
+++ b/7-Haskell/day2.hs	Tue Jun 18 21:05:00 2019 +0100
@@ -55,4 +55,23 @@
     -- Wilson's theorem seems easiest: https://en.wikipedia.org/wiki/Wilson%27s_theorem
     primes :: [Integer]
     -- Primes after 2 have to be odd (or else they're a multiple of 2!), so increment up the odd numbers
-    primes = 2 : [x | x <- [3, 5 ..], (mod ((product [1 .. x-1]) + 1) x) == 0]
\ No newline at end of file
+    primes = 2 : [x | x <- [3, 5 ..], (mod ((product [1 .. x-1]) + 1) x) == 0]
+
+    break_lines :: String -> Int -> [String]
+    break_lines str len = break_lines' str "" "" len []
+
+    break_lines' :: String -> String -> String -> Int -> [String] -> [String]
+    break_lines' "" "" "" _ strings = strings
+    break_lines' "" next_word line len strings = break_lines' "" "" "" len (strings ++ [line ++ next_word])
+    break_lines' (char:rest) next_word line len strings
+        | char == ' ' && candidate_length == len = break_lines' rest "" "" len (strings ++ [line ++ next_word]) -- if we've got a space at the right place, add the word but not the space
+        | char == ' ' = break_lines' rest "" (line ++ next_word ++ " ") len strings -- else we've got a break so add the word and the space to the line
+        -- Then, for non-space characters…
+        | candidate_length < len = break_lines' rest (next_word ++ [char]) line len strings -- if we're not at the line length then add the character
+        | candidate_length == len && line /= "" = break_lines' rest (next_word ++ [char]) "" len (strings ++ [line]) -- if we've got a partial line and our next word is getting too long then add the line as-is
+        | length next_word == len = break_lines' rest ("-" ++ [char]) "" len (strings ++ [next_word]) -- if our candidate is more than our length and we've got a blank line then add our N characters of this word, and hyphenate the word
+        | otherwise = break_lines' rest (next_word ++ [char]) line len strings -- otherwise we're within limits and can keep going
+        where candidate_length = (length next_word + length line)
+
+-- > break_lines "hello 1234567890123456789012345678901234567890123456789012345678901234567890123456789012345 lorem ipsum bibbety bobbety boo once upon a time there was a cat and it sat on a mat while the quick brown fox jumped over the lazy dog" 80
+--   ["hello ","12345678901234567890123456789012345678901234567890123456789012345678901234567890","-12345 lorem ipsum bibbety bobbety boo once upon a time there was a cat and it ","sat on a mat while the quick brown fox jumped over the lazy dog"]--