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Make bottomUpFilter better by also removing categories which contain no finite strings.

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bringert
2007-06-27 16:27:55 +00:00
parent 836e596189
commit f664497bcd
1 changed files with 18 additions and 3 deletions
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21
src/GF/Speech/TransformCFG.hs
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@@ -41,7 +41,6 @@ import Data.Monoid (mconcat)
import Data.Set (Set)
import qualified Data.Set as Set
-- not very nice to replace the structured CFCat type with a simple string
type CFRule_ = CFRule Cat_ CFTerm Token
@@ -104,14 +103,21 @@ removeCycles = groupProds . f . ungroupProds
-- | Removes productions which use categories which have no productions.
-- Only does one pass through the grammar.
bottomUpFilter :: CFRules -> CFRules
bottomUpFilter rs = k'
bottomUpFilter_old :: CFRules -> CFRules
bottomUpFilter_old rs = k'
where
keep = filter (not . null . snd) rs
allCats = nub [c | (_,r) <- rs, CFRule _ rhs _ <- r, Cat c <- rhs]
emptyCats = filter (nothingOrNull . flip lookup rs) allCats
k' = map (\ (c,xs) -> (c, filter (not . anyUsedBy emptyCats) xs)) keep
-- | Better bottom-up filter that also removes categories which contain no finite
-- strings.
bottomUpFilter :: CFRules -> CFRules
bottomUpFilter gr = fix grow []
where grow g = g `unionCFRules` filterCFRules (all (okSym g) . ruleRhs) gr
okSym g = symbol (`elem` allCats g) (const True)
-- | Removes categories which are not reachable from the start category.
-- Only does one pass through the grammar.
topDownFilter :: Cat_ -> CFRules -> CFRules
@@ -305,6 +311,15 @@ catRules rs c = fromMaybe [] (lookup c rs)
catSetRules :: CFRules -> Set Cat_ -> [CFRule_]
catSetRules g cs = concat [rs | (c,rs) <- g, c `Set.member` cs]
unionCFRules :: CFRules -> CFRules -> CFRules
unionCFRules x y = Map.toList $ Map.map Set.toList $ Map.unionWith Set.union (fromCFRules x) (fromCFRules y)
where
fromCFRules :: CFRules -> Map Cat_ (Set CFRule_)
fromCFRules g = Map.fromListWith Set.union [(c, Set.fromList rs) | (c,rs) <- g]
filterCFRules :: (CFRule_ -> Bool) -> CFRules -> CFRules
filterCFRules p gr = [(c,rs') | (c,rs) <- gr, let rs' = filter p rs, not (null rs')]
lhsCat :: CFRule c n t -> c
lhsCat (CFRule c _ _) = c