Optimizing Haskell code

Question

I\'m trying to learn Haskell and after an article in reddit about Markov text chains, I decided to implement Markov text generation first in Python and now in Haskell. Howev

Answer 1

Here's a foldl'-based version that seems to be about twice as fast as your train:

train' :: [B.ByteString] -> Database
train' xs = foldl' (flip f) M.empty $ zip3 xs (tail xs) (tail $ tail xs)
  where
    f (a, b, c) = M.insertWith (M.unionWith (+)) (a, b) (M.singleton c 1)

I tried it on the Project Gutenberg Huckleberry Finn (which I assume is your 76.txt), and it produces the same output as your function. My timing comparison was very unscientific, but this approach is probably worth a look.