OK. Again, not sure what going on here. Pattern looks OK to me.
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),all@(w1:words)) <- get if (Prelude.null all)
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) [w1] mp, (pfx2,w1), words)
buildMap
=============================
*Main> :r[1 of 1] Compiling Main ( markov3.hs, interpreted )Ok,
modules loaded: Main.*Main> fst $ runState buildMap (singleton ("\n","\n") [],
("\n","\n"), ["I","am","lost."])fromList *** Exception: Pattern match failure
in do expression at markov3.hs:13:14-44
--- On Thu, 5/19/11, michael rice <[email protected]> wrote:
From: michael rice <[email protected]>
Subject: Re: [Haskell-cafe] Trying to return a map from State monad
To: "Thedward Blevins" <[email protected]>
Cc: [email protected]
Date: Thursday, May 19, 2011, 12:41 PM
Ok, I see I left out the "State" word.
Should be: type GeneratorState = State (Map Prefix [String],Prefix,[String])
Thanks,
Michael
--- On Thu, 5/19/11, Thedward Blevins <[email protected]> wrote:
From: Thedward Blevins <[email protected]>
Subject: Re: [Haskell-cafe] Trying to return a map from State monad
To: "michael rice" <[email protected]>
Cc: [email protected]
Date: Thursday, May 19, 2011, 12:22 PM
On Thu, May 19, 2011 at 11:03, michael rice <[email protected]> wrote:
> type GeneratorState = (Map Prefix [String],Prefix,[String])
> buildMap :: GeneratorState (Map Prefix [String])
You are trying to use a type alias (GeneratorState) as a type constructor.
There may be other problems, but that leaps out.
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