10-lines for CKY parsing in Haskell

CKY.hs

mkChart :: (Eq cat, Eq term) =>
  CFG cat term -> [term] -> [((Int, Int), [cat])]
mkChart g xs = helper (0,1) [] where
  helper p@(i,j) tab
    | j>length xs = tab
    | i<0         = helper (j,j+1) tab
    | i==j-1      = helper (i-1,j) $
                      (p, [n | n:-t <- g, t==xs!!(j-1)]):tab
    | otherwise   = helper (i-1,j) $
                      (p, [n | n:>(l,r) <- g, k <- [i+1..j-1],
                               lc <- fromJust $ lookup (i,k) tab, l==lc,
                               rc <- fromJust $ lookup (k,j) tab, r==rc]):tab

parseCYK :: (Eq cat, Eq term) => CFG cat term -> [term] -> [cat]
parseCYK g xs = snd $ head $ mkChart g xs