What am I doing wrong in the last line of main? If I comment out the last line of main, my program prints the map (mp) that is created. If I leave it in, the program fails. The last line should print the list ["I"]. Michael ================================================ import Control.Monad.Stateimport Data.Map type Prefix = (String,String)type GeneratorState = State ((Map Prefix [String]),Prefix,[String]) non_word = "\n" f key new old = new ++ old buildMap :: GeneratorState (Map Prefix [String])buildMap = do (mp,(pfx1,pfx2),words) <- get if (Prelude.null words) then {- No more words. Return final map (adding non_word for prefix). -} return (insertWithKey' f (pfx1,pfx2) [non_word] mp) else do {- Add word to map at prefix & continue. -} put (insertWithKey' f (pfx1,pfx2) [head words] mp, (pfx2,(head words)), tail words) buildMap {-*Main> execState buildMap (singleton ("\n","\n") [], ("\n","\n"), ["I","am","lost."])(fromList [(("\n","\n"),["I"]),(("\n","I"),["am"]),(("I","am"),["lost."])],("am","lost."),[])*Main> -} nwords = 1 main = do contents <- getContents let mp = execState buildMap (singleton (non_word,non_word) [], (non_word,non_word), words contents) putStrLn $ show mp putStrLn $ show (mp ! (non_word,non_word)) ============================================== [michael@hostname ~]$ ghc --make markov4.hs[1 of 1] Compiling Main ( markov4.hs, markov4.o )Linking markov4 ...[michael@hostname ~]$ echo "I am lost." | ./markov4(fromList [(("\n","\n"),["I"]),(("\n","I"),["am"]),(("I","am"),["lost."])],("am","lost."),[])[michael@hostname ~]$ ghc --make markov4.hs[1 of 1] Compiling Main ( markov4.hs, markov4.o ) markov4.hs:35:27: Couldn't match expected type `Map k a' against inferred type `(Map Prefix [String], Prefix, [String])' In the first argument of `(!)', namely `mp' In the first argument of `show', namely `(mp ! (non_word, non_word))' In the second argument of `($)', namely `show (mp ! (non_word, non_word))'[michael@hostname ~]$