forked from GitHub/gf-core
102 lines
3.5 KiB
Haskell
102 lines
3.5 KiB
Haskell
----------------------------------------------------------------------
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-- |
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-- Maintainer : PL
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-- Stability : (stable)
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-- Portability : (portable)
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--
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-- > CVS $Date: 2005/04/11 13:52:51 $
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-- > CVS $Author: peb $
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-- > CVS $Revision: 1.1 $
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--
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-- CFG parsing with a general chart
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-----------------------------------------------------------------------------
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module GF.NewParsing.CFG.General
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(parse, Strategy) where
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import GF.System.Tracing
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import GF.Infra.Print
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import GF.Formalism.Utilities
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import GF.Formalism.CFG
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import GF.NewParsing.CFG.PInfo
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import GF.NewParsing.GeneralChart
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import GF.Data.Assoc
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import Monad
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--parse :: (Ord n, Ord c, Ord t) => Strategy -> CFParser c n t
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parse strategy grammar start = extract .
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tracePrt "#internal chart" (prt . length . chartList) .
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process strategy grammar start
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type Strategy = (Bool, Bool) -- ^ (isBottomup, isTopdown)
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extract :: (Ord n, Ord c, Ord t) =>
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IChart n (Symbol c t) -> CFChart c n t
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extract chart = [ CFRule (Edge j k cat) daughters name |
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Edge j k (Cat cat, found, [], Just name) <- chartList chart,
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daughters <- path j k (reverse found) ]
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where path i k [] = [ [] | i==k ]
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path i k (Tok tok : found)
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= [ Tok tok : daughters |
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daughters <- path (i+1) k found ]
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path i k (Cat cat : found)
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= [ Cat (Edge i j cat) : daughters |
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Edge _i j _cat <- chartLookup chart (Passive (Cat cat) i),
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daughters <- path j k found ]
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process :: (Ord n, Ord c, Ord t) =>
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Strategy -- ^ (isBottomup, isTopdown) :: (Bool, Bool)
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-> CFPInfo c n t -- ^ parser information (= grammar)
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-> [c] -- ^ list of starting categories
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-> Input t -- ^ input string
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-> IChart n (Symbol c t)
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process (isBottomup, isTopdown) grammar start
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= trace2 "CFParserGeneral" ((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 = ParseChart (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
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= Edge i k (cat, next:found, tofind, name)
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loopingEdge k (CFRule cat tofind name) = Edge k k (Cat cat, [], tofind, Just name)
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