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OK. Again, not sure what going on here. Pattern looks OK to me.
Michael
=============================
import Control.Monad.State
import 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 <nowgate@yahoo.com> wrote:
From: michael rice <nowgate@yahoo.com>
Subject: Re: [Haskell-cafe] Trying to return a map from State monad
To: "Thedward Blevins" <thedward@barsoom.net>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 <thedward@barsoom.net> wrote:
From: Thedward Blevins <thedward@barsoom.net>
Subject: Re: [Haskell-cafe] Trying to return a map from State monad
To: "michael rice" <nowgate@yahoo.com>
Cc: haskell-cafe@haskell.org
Date: Thursday, May 19, 2011, 12:22 PM
On Thu, May 19, 2011 at 11:03, michael rice < nowgate@yahoo.com> 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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