"Committed_by_peb"

src/GF/Parsing/ParseCFG/General.hs

@@ -0,0 +1,84 @@
+----------------------------------------------------------------------
+-- |
+-- Module      : CFParserGeneral
+-- Maintainer  : Peter Ljunglöf
+-- Stability   : (stable)
+-- Portability : (portable)
+--
+-- > CVS $Date: 2005/03/21 22:31:54 $ 
+-- > CVS $Author: peb $
+-- > CVS $Revision: 1.1 $
+--
+-- Several implementations of CFG chart parsing
+-----------------------------------------------------------------------------
+
+module GF.Parsing.ParseCFG.General 
+    (parse, Strategy) where
+
+import Tracing
+
+import GF.Parsing.Utilities
+import GF.Parsing.CFGrammar
+import GF.Parsing.GeneralChart 
+import GF.Data.Assoc
+
+parse :: (Ord n, Ord c, Ord t) => Strategy -> CFParser n c t
+parse strategy grammar start = extract . process strategy grammar start
+
+type Strategy = (Bool, Bool) -- (isBottomup, isTopdown)
+
+extract :: [Item n (Symbol c t)] -> [Edge (Rule n c t)]
+extract edges =
+    edges'
+    where edges' = [ Edge j k (Rule cat (reverse found) name) |
+		     Edge j k (Cat cat, found, [], Just name) <- edges ]
+
+process :: (Ord n, Ord c, Ord t) => Strategy -> PInfo n c t -> 
+	   [c] -> Input t -> [Item n (Symbol c t)]
+process (isBottomup, isTopdown) grammar start
+    = trace ("CFParserGeneral" ++ 
+	     (if isBottomup then " BU" else "") ++ 
+	     (if isTopdown  then " TD" else "")) $
+      buildChart keyof [predict, combine] . axioms 
+    where axioms input = initial ++ scan input
+
+          scan input = map (fmap mkEdge) (inputEdges input)
+	  mkEdge tok = (Tok tok, [], [], Nothing)
+
+          -- the combine rule
+          combine chart (Edge j k (next, _, [], _))
+	      = [ edge `forwardTo` k | edge <- chartLookup chart (Active next j) ]
+          combine chart edge@(Edge _ j (_, _, next:_, _))
+	      = [ edge `forwardTo` k | Edge _ k _ <- chartLookup chart (Passive next j) ]
+
+          -- initial predictions
+          initial = [ loopingEdge 0 rule | cat <- start, rule <- tdRuleLookup ? cat ]
+
+          -- predictions
+          predict chart (Edge j k (next, _, [], _)) | isBottomup 
+	      = [ loopingEdge j rule `forwardTo` k | rule <- bottomupRules grammar ? next ]
+	      -- - - - - - - - - -   ^^^^^^^^^^^^^ Kilbury prediction: move dot forward
+	  predict chart (Edge _ k (_, _, Cat cat:_, _))
+	      = [ loopingEdge k rule | rule <- tdRuleLookup ? cat ]
+	  predict _ _ = []
+
+          tdRuleLookup | isTopdown  = topdownRules grammar
+		       | isBottomup = emptyLeftcornerRules grammar
+
+-- internal representation of parse items
+
+type Item   n s = Edge (s, [s], [s], Maybe n)
+type IChart n s = Chart (Item n s) (IKey s)
+data IKey     s = Active  s Int
+		| Passive s Int
+		  deriving (Eq, Ord, Show)
+
+keyof (Edge _ j (_, _, next:_, _)) = Active next j
+keyof (Edge j _ (cat, _, [], _))   = Passive cat j
+
+forwardTo (Edge i j (cat, found, next:tofind, name)) k = Edge i k (cat, next:found, tofind, name)
+
+loopingEdge k (Rule cat tofind name) = Edge k k (Cat cat, [], tofind, Just name)
+
+
+