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86 lines
2.8 KiB
Haskell
86 lines
2.8 KiB
Haskell
----------------------------------------------------------------------
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-- |
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-- Module : CFParserGeneral
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-- Maintainer : Peter Ljunglöf
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-- Stability : (stable)
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-- Portability : (portable)
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--
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-- > CVS $Date: 2005/03/21 14:17:41 $
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-- > CVS $Author: peb $
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-- > CVS $Revision: 1.1 $
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--
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-- Several implementations of CFG chart parsing
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-----------------------------------------------------------------------------
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module GF.Parsing.CFParserGeneral (parse,
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Strategy
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) where
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import Tracing
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import GF.Parsing.Parser
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import GF.Conversion.CFGrammar
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import GF.Parsing.GeneralChart
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import GF.Data.Assoc
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parse :: (Ord n, Ord c, Ord t) => Strategy -> CFParser n c t
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parse strategy grammar start = extract . process strategy grammar start
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type Strategy = (Bool, Bool) -- (isBottomup, isTopdown)
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extract :: [Item n (Symbol c t)] -> [Edge (Rule n c t)]
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extract edges =
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edges'
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where edges' = [ Edge j k (Rule cat (reverse found) name) |
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Edge j k (Cat cat, found, [], Just name) <- edges ]
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process :: (Ord n, Ord c, Ord t) => Strategy -> PInfo n c t ->
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[c] -> Input t -> [Item n (Symbol c t)]
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process (isBottomup, isTopdown) grammar start
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= trace ("CFParserGeneral" ++
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(if isBottomup then " BU" else "") ++
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(if isTopdown then " TD" else "")) $
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buildChart keyof [predict, combine] . axioms
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where axioms input = initial ++ scan input
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scan input = map (fmap mkEdge) (inputEdges input)
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mkEdge tok = (Tok tok, [], [], Nothing)
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-- the combine rule
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combine chart (Edge j k (next, _, [], _))
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= [ edge `forwardTo` k | edge <- chartLookup chart (Active next j) ]
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combine chart edge@(Edge _ j (_, _, next:_, _))
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= [ edge `forwardTo` k | Edge _ k _ <- chartLookup chart (Passive next j) ]
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-- initial predictions
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initial = [ loopingEdge 0 rule | cat <- start, rule <- tdRuleLookup ? cat ]
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-- predictions
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predict chart (Edge j k (next, _, [], _)) | isBottomup
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= [ loopingEdge j rule `forwardTo` k | rule <- bottomupRules grammar ? next ]
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-- - - - - - - - - - ^^^^^^^^^^^^^ Kilbury prediction: move dot forward
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predict chart (Edge _ k (_, _, Cat cat:_, _))
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= [ loopingEdge k rule | rule <- tdRuleLookup ? cat ]
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predict _ _ = []
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tdRuleLookup | isTopdown = topdownRules grammar
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| isBottomup = emptyLeftcornerRules grammar
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-- internal representation of parse items
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type Item n s = Edge (s, [s], [s], Maybe n)
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type IChart n s = Chart (Item n s) (IKey s)
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data IKey s = Active s Int
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| Passive s Int
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deriving (Eq, Ord, Show)
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keyof (Edge _ j (_, _, next:_, _)) = Active next j
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keyof (Edge j _ (cat, _, [], _)) = Passive cat j
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forwardTo (Edge i j (cat, found, next:tofind, name)) k = Edge i k (cat, next:found, tofind, name)
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loopingEdge k (Rule cat tofind name) = Edge k k (Cat cat, [], tofind, Just name)
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