s b (q:r) = s (z q b) r s a [] = a z (f:l:_) ((a,c):b) | a == l = ((a,f:c):b) | True = (a,c):(z (f:[l]) b) z (f:l:_) [] = [(l,[f])] o ((l,f):r) = (l++(y f)++"\n")++(o r) o [] = [] y (a:[]) = ' ':a y (a:b) = m (a:b) m (a:b) = ("\n\t"++a)++(m b) m [] = [] g = o . (s []) . (map words) . lines main = do x

First one to figure out what it does gets a cookie. Allegators and Jolle expressely forbidden from participating.

Edit:

Through the valiant effort and sacrifice of myself and Jolle, we've managed to produce an even shorter, albeit arguably less obfuscated, version of the above: