refactor GF.Data.BacktrackM to use the MonadState and Functor classes

3 files changed, 38 insertions, 45 deletions

diff --git a/src/GF/Compile/GenerateFCFG.hs b/src/GF/Compile/GenerateFCFG.hs
index 108976506..a0f82218c 100644
--- a/src/GF/Compile/GenerateFCFG.hs
+++ b/src/GF/Compile/GenerateFCFG.hs
@@ -261,7 +261,7 @@ evalTerm cnc_defs path x = error ("evalTerm ("++show x++")")
 
 unifyPType :: FIndex -> FPath -> Term -> CnvMonad FIndex
 unifyPType nr path (C max_index) =
-    do (_, args, _, _) <- readState
+    do (_, args, _, _) <- get
        let (PFCat _ _ tcs,_) = args !! nr
        case lookup path tcs of
          Just index -> return index
@@ -390,7 +390,7 @@ genFCatArg cnc_defs ctype env@(GrammarEnv last_id catSet seqSet funSet prodSet)
     gen_tcs (C max_index) path acc =
       case List.lookup path tcs of
         Just index -> return $! addConstraint path index acc
-        Nothing    -> do writeState True
+        Nothing    -> do put True
                          index <- member [0..max_index]
                          return $! addConstraint path index acc
       where
@@ -498,21 +498,21 @@ mkSelector rcs tcss =
 -- updating the MCF rule
 
 readArgCType :: FIndex -> CnvMonad Term
-readArgCType nr = do (_, _, _, ctypes) <- readState
+readArgCType nr = do (_, _, _, ctypes) <- get
 		     return (ctypes !! nr)
 
 restrictArg :: FIndex -> FPath -> FIndex -> CnvMonad ()
 restrictArg nr path index = do
-  (head, args, ctype, ctypes) <- readState 
+  (head, args, ctype, ctypes) <- get 
   args' <- updateNthM (\(xcat,xs) -> do xcat <- restrictProtoFCat path index xcat
                                         return (xcat,xs)                         ) nr args
-  writeState (head, args', ctype, ctypes)
+  put (head, args', ctype, ctypes)
 
 projectArg :: FIndex -> FPath -> CnvMonad Int
 projectArg nr path = do
-  (head, args, ctype, ctypes) <- readState
+  (head, args, ctype, ctypes) <- get
   (xnr,args') <- updateArgs nr args
-  writeState (head, args', ctype, ctypes)
+  put (head, args', ctype, ctypes)
   return xnr
   where
     updateArgs :: FIndex -> [(ProtoFCat,[FPath])] -> CnvMonad (Int,[(ProtoFCat,[FPath])])
@@ -525,20 +525,20 @@ projectArg nr path = do
       return (xnr,a:as)
 
 readHeadCType :: CnvMonad Term
-readHeadCType = do (_, _, ctype, _) <- readState
+readHeadCType = do (_, _, ctype, _) <- get
 		   return ctype
 
 restrictHead :: FPath -> FIndex -> CnvMonad ()
 restrictHead path term
-    = do (head, args, ctype, ctypes) <- readState
+    = do (head, args, ctype, ctypes) <- get
 	 head' <- restrictProtoFCat path term head
-	 writeState (head', args, ctype, ctypes)
+	 put (head', args, ctype, ctypes)
 
 projectHead :: FPath -> CnvMonad ()
 projectHead path
-    = do (head, args, ctype, ctypes) <- readState
+    = do (head, args, ctype, ctypes) <- get
 	 head' <- projectProtoFCat path head
-	 writeState (head', args, ctype, ctypes)
+	 put (head', args, ctype, ctypes)
 
 restrictProtoFCat :: FPath -> FIndex -> ProtoFCat -> CnvMonad ProtoFCat
 restrictProtoFCat path0 index0 (PFCat cat rcs tcs) = do
diff --git a/src/GF/Compile/GeneratePMCFG.hs b/src/GF/Compile/GeneratePMCFG.hs
index 6a5f9ebdf..0ae32d483 100644
--- a/src/GF/Compile/GeneratePMCFG.hs
+++ b/src/GF/Compile/GeneratePMCFG.hs
@@ -160,7 +160,7 @@ convertArg (C max) nr path lbl_path lin lins = do
   restrictArg nr path index
   return lins
 convertArg (S _) nr path lbl_path lin lins = do
-  (_, args) <- readState
+  (_, args) <- get
   let PFCat _ cat rcs tcs = args !! nr
       l = index path rcs 0
       sym | isLiteralCat cat = FSymLit nr l
@@ -190,7 +190,7 @@ convertRec cnc_defs (index:sub_sel) ctype record lbl_path lin lins = do
 -- eval a term to ground terms
 
 evalTerm :: TermMap -> FPath -> Term -> CnvMonad FIndex
-evalTerm cnc_defs path (V nr)       = do (_, args) <- readState
+evalTerm cnc_defs path (V nr)       = do (_, args) <- get
 		                         let PFCat _ _ _ tcs = args !! nr
 		                             rpath = reverse path
                                          index <- member (fromMaybe (error "evalTerm: wrong path") (lookup rpath tcs))
@@ -349,15 +349,15 @@ getFCats (GrammarEnv last_id catSet seqSet funSet crcSet prodSet) (PFCat n cat r
 
 restrictArg :: FIndex -> FPath -> FIndex -> CnvMonad ()
 restrictArg nr path index = do
-  (head, args) <- readState 
+  (head, args) <- get
   args' <- updateNthM (restrictProtoFCat path index) nr args
-  writeState (head, args')
+  put (head, args')
 
 restrictHead :: FPath -> FIndex -> CnvMonad ()
 restrictHead path term
-    = do (head, args) <- readState
+    = do (head, args) <- get
 	 head' <- restrictProtoFCat path term head
-	 writeState (head', args)
+	 put (head', args)
 
 restrictProtoFCat :: FPath -> FIndex -> ProtoFCat -> CnvMonad ProtoFCat
 restrictProtoFCat path0 index0 (PFCat n cat rcs tcs) = do
diff --git a/src/GF/Data/BacktrackM.hs b/src/GF/Data/BacktrackM.hs
index 790d11a83..36317ebb6 100644
--- a/src/GF/Data/BacktrackM.hs
+++ b/src/GF/Data/BacktrackM.hs
@@ -13,24 +13,24 @@
 -----------------------------------------------------------------------------
 
 {-# OPTIONS_GHC -fglasgow-exts #-}
-module GF.Data.BacktrackM ( -- * the backtracking state monad
+module GF.Data.BacktrackM (
+                    -- * the backtracking state monad
 		    BacktrackM,
-		    -- * controlling the monad
-		    failure,
-		    (|||),
-		    -- * handling the state & environment
-		    readState,
-		    writeState,
 		    -- * monad specific utilities
 		    member,
+		    cut,
 		    -- * running the monad
 		    foldBM,          runBM,
 		    foldSolutions,   solutions,
-		    foldFinalStates, finalStates
+		    foldFinalStates, finalStates,
+		    
+		    -- * reexport the 'MonadState' class
+		    module Control.Monad.State.Class,
 		  ) where
 
 import Data.List
 import Control.Monad
+import Control.Monad.State.Class
 
 ----------------------------------------------------------------------
 -- Combining endomorphisms and continuations
@@ -60,34 +60,27 @@ foldFinalStates f b (BM m) s = m (\x s b -> f s b) s b
 finalStates :: BacktrackM s () -> s -> [s]
 finalStates bm = map fst . runBM bm
 
-
--- * handling the state & environment
-
-readState :: BacktrackM s s
-readState    = BM (\c s b -> c s s b)
-
-writeState :: s -> BacktrackM s ()
-writeState s = BM (\c _ b -> c () s b)
-
 instance Monad (BacktrackM s) where
     return a   = BM (\c s b -> c a s b)
     BM m >>= k = BM (\c s b -> m (\a s b -> unBM (k a) c s b) s b)
 	where unBM (BM m) = m
-    fail _ = failure
+    fail _ = mzero
 
--- * controlling the monad
-
-failure :: BacktrackM s a
-failure = BM (\c s b -> b)
-
-(|||) :: BacktrackM s a -> BacktrackM s a -> BacktrackM s a
-(BM f) ||| (BM g) = BM (\c s b -> g c s $! f c s b)
+instance Functor (BacktrackM s) where
+    fmap f (BM m) = BM (\c s b -> m (\a s b -> c (f a) s b) s b)
 
 instance MonadPlus (BacktrackM s) where
-    mzero = failure
-    mplus = (|||)
+    mzero                 = BM (\c s b -> b)
+    (BM f) `mplus` (BM g) = BM (\c s b -> g c s $! f c s b)
+
+instance MonadState s (BacktrackM s) where
+  get = BM (\c s b -> c s s b)
+  put s = BM (\c _ b -> c () s b)
 
 -- * specific functions on the backtracking monad
 
 member :: [a] -> BacktrackM s a
 member xs = BM (\c s b -> foldl' (\b x -> c x s b) b xs)
+
+cut :: BacktrackM s a -> BacktrackM s [(s,a)]
+cut f = BM (\c s b -> c (runBM f s) s b)