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|
----------------------------------------------------------------------
-- |
-- Module : ParseCFG.General
-- Maintainer : Peter Ljunglöf
-- Stability : (stable)
-- Portability : (portable)
--
-- > CVS $Date: 2005/04/21 16:23:00 $
-- > CVS $Author: bringert $
-- > CVS $Revision: 1.2 $
--
-- Several implementations of CFG chart parsing
-----------------------------------------------------------------------------
module GF.OldParsing.ParseCFG.General
(parse, Strategy) where
import GF.System.Tracing
import GF.OldParsing.Utilities
import GF.OldParsing.CFGrammar
import GF.OldParsing.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
= trace2 "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)
|
