A laugh a minute. I though of that and tried it but got the same response (forgetting to :r my source) before rerunning. Time for a break. Thanks! Michael --- On Thu, 5/19/11, aditya siram <aditya.si...@gmail.com> wrote:
From: aditya siram <aditya.si...@gmail.com> Subject: Re: [Haskell-cafe] Trying to return a map from State monad To: "michael rice" <nowg...@yahoo.com> Cc: "Thedward Blevins" <thedw...@barsoom.net>, haskell-cafe@haskell.org Date: Thursday, May 19, 2011, 4:57 PM The problem is that the "all@(w1:words)" pattern-match fails when "all" is empty. The quick and dirty fix is: import Control.Monad.State import Data.Map import Debug.Trace 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) <- 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) [head all] mp, (pfx2,head all), tail all) buildMap *Main> fst $ runState buildMap (singleton ("\n","\n") [], ("\n","\n"), ["I","am","lost."]) fromList [(("\n","\n"),["I"]),(("\n","I"),["am"]),(("I","am"),["lost."]),(("am","lost."),["\n"])] A better one would be to write a helper function that correctly pattern matched on the list. -deech On Thu, May 19, 2011 at 3:30 PM, michael rice <nowg...@yahoo.com> wrote: 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 <nowg...@yahoo.com> wrote: From: michael rice <nowg...@yahoo.com> Subject: Re: [Haskell-cafe] Trying to return a map from State monad To: "Thedward Blevins" <thedw...@barsoom.net> Cc: haskell-cafe@haskell.org 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 <thedw...@barsoom.net> wrote: From: Thedward Blevins <thedw...@barsoom.net> Subject: Re: [Haskell-cafe] Trying to return a map from State monad To: "michael rice" <nowg...@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 <nowg...@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. -----Inline Attachment Follows----- _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
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