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{-- Module --------------------------------------------------------------------
Filename: ActiveParse.hs
Author: Håkan Burden
Time-stamp: <2005-04-18, 14:25>
Description: An agenda-driven implementation of algorithm 4.6, Active parsing
of PMCFG, as described in Ljunglöf (2004)
------------------------------------------------------------------------------}
module ActiveParse where
-- GF modules
import Examples
import GeneralChart
import MCFGrammar
import MCFParser
import Nondet
import Parser
import Range
{-- Datatypes -----------------------------------------------------------------
AChart: A RedBlackMap with Items and Keys
Item :
AKey :
------------------------------------------------------------------------------}
data Item n c l = Active (AbstractRule n c)
(RangeRec l)
Range
(Lin c l Range)
(LinRec c l Range)
[RangeRec l]
| Passive (AbstractRule n c) (RangeRec l) [RangeRec l]
deriving (Eq, Ord, Show)
type AChart n c l = ParseChart (Item n c l) (AKey c)
data AKey c = Act c
| Pass c
| Useless
deriving (Eq, Ord, Show)
keyof :: Item n c l -> AKey c
keyof (Active _ _ _ (Lin _ (Cat (next, _, _):_)) _ _) = Act next
keyof (Passive (_, cat, _) _ _) = Pass cat
keyof _ = Useless
{-- Parsing -------------------------------------------------------------------
recognize:
parse : Builds a chart from the initial agenda, given by prediction, and
the inference rules
keyof : Given an Item returns an appropriate Key for the Chart
------------------------------------------------------------------------------}
recognize strategy mcfg toks = chartMember
(parse strategy mcfg toks) item (keyof item)
where n = length toks
n2 = n `div` 2
item = (Passive ("f", S, [A])
[("s",Range (0,n))]
[[("p",Range (0,n2)),("q",Range (n2,n))]])
parse :: (Ord n, Ord c, Ord l, Eq t) => Strategy -> Grammar n c l t -> [t]
-> ParseChart (Item n c l) (AKey c)
parse (False,False) mcfg toks = buildChart keyof
[complete, scan, combine, convert]
(predict mcfg toks)
parse (True, False) mcfg toks = buildChart keyof
[predictKilbury mcfg toks, complete, combine, convert]
(terminal mcfg toks)
parse (False, True) mcfg toks = buildChart keyof
[predictEarley mcfg toks, complete, scan, combine, convert]
(initial (take 1 mcfg) toks)
predictKilbury mcfg toks _ (Passive (_, cat, _) found _) =
[ Active (f, a, rhs) [] rng lin' lins' daughters |
Rule a rhs ((Lin l ((Cat (cat', r, i)):syms)):lins) f <- mcfg,
cat == cat',
lin' : lins' <- solutions $ rangeRestRec toks (Lin l syms : lins),
-- lins' <- solutions $ rangeRestRec toks lins,
rng <- solutions $ projection r found,
let daughters = (replaceRec (replicate (length rhs) []) i found) ]
predictKilbury _ _ _ _ = []
predictEarley mcfg toks _ item@(Active _ _ _ (Lin _ ((Cat (cat, _, _)):_)) _ _) =
concat [ predEar toks item rule |
rule@(Rule cat' _ _ _) <- mcfg, cat == cat' ]
predictEarley _ _ _ _ = []
predEar toks _ (Rule cat [] lins f) =
[ Passive (f, cat, []) (makeRangeRec lins') [] |
lins' <- solutions $ rangeRestRec toks lins ]
predEar toks (Active _ _ (Range (_,j)) _ _ _) (Rule cat rhs lins f) =
[ Active (f, cat, rhs) [] (Range (j, j)) lin' lins' (replicate (length rhs) []) |
(lin':lins') <- solutions $ rangeRestRec toks lins ]
predEar toks (Active _ _ EmptyRange _ _ _) (Rule cat rhs lins f) =
[ Active (f, cat, rhs) [] EmptyRange lin' lins' (replicate (length rhs) []) |
(lin':lins') <- solutions $ rangeRestRec toks lins ]
{--Inference rules ------------------------------------------------------------
predict : Creates an Active Item of every Rule in the Grammar to give the
initial Agenda
complete:
scan :
combine : Creates an Active Item every time it is possible to combine
an Active Item from the agenda with a Passive Item from the Chart
convert : Active Items with nothing to find are converted to Passive Items
------------------------------------------------------------------------------}
predict :: Eq t => Grammar n c l t -> [t] -> [Item n c l]
predict grammar toks = [ Active (f, cat, rhs) [] EmptyRange lin' lins'
(replicate (length rhs) []) |
Rule cat rhs lins f <- grammar,
(lin':lins') <- solutions $ rangeRestRec toks lins ]
complete :: (Ord n, Ord c, Ord l) => ParseChart (Item n c l) (AKey c) -> Item n c l
-> [Item n c l]
complete _ (Active rule found (Range (i, j)) (Lin l []) (lin:lins) recs) =
[ Active rule (found ++ [(l, Range (i,j))]) EmptyRange lin lins recs ]
complete _ _ = []
scan :: (Ord n, Ord c, Ord l) => ParseChart (Item n c l) (AKey c) -> Item n c l
-> [Item n c l]
scan _ (Active rule found rng (Lin l ((Tok rng'):syms)) lins recs) =
[ Active rule found rng'' (Lin l syms) lins recs |
rng'' <- solutions $ concRanges rng rng' ]
scan _ _ = []
combine :: (Ord n, Ord c, Ord l) => ParseChart (Item n c l) (AKey c) -> Item n c l
-> [Item n c l]
combine chart (Active rule found rng (Lin l ((Cat (c, r, d)):syms)) lins recs) =
[ Active rule found rng'' (Lin l syms) lins (replaceRec recs d found') |
Passive _ found' _ <- chartLookup chart (Pass c),
rng' <- solutions $ projection r found',
rng'' <- solutions $ concRanges rng rng',
subsumes (recs !! d) found' ]
combine chart (Passive (_, c, _) found _) =
[ Active rule found' rng (Lin l syms) lins (replaceRec recs' d found) |
Active rule found' rng' (Lin l ((Cat (c, r, d)):syms)) lins recs'
<- chartLookup chart (Act c),
rng'' <- solutions $ projection r found,
rng <- solutions $ concRanges rng' rng'',
subsumes (recs' !! d) found ]
combine _ _ = []
convert :: (Ord n, Ord c, Ord l) => ParseChart (Item n c l) (AKey c) -> Item n c l
-> [Item n c l]
convert _ (Active rule found rng (Lin l []) [] recs) =
[ Passive rule (found ++ [(l, rng)]) recs ]
convert _ _ = []
-- Earley --
-- anropas med alla startregler
initial :: Eq t => [Rule n c l t] -> [t] -> [Item n c l]
initial starts toks =
[ Active (f, s, rhs) [] (Range (0, 0)) lin' lins' (replicate (length rhs) []) |
Rule s rhs lins f <- starts,
(lin':lins') <- solutions $ rangeRestRec toks lins ]
-- Kilbury --
terminal mcfg toks =
[ Passive (f, cat, []) (makeRangeRec lins') [] |
Rule cat [] lins f <- mcfg,
lins' <- solutions $ rangeRestRec toks lins ]
|
