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Also remove indirectly cyclic productions.

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bringert
2007-03-25 16:34:35 +00:00
parent 935b60f977
commit 4905996816
1 changed files with 10 additions and 2 deletions
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12
src/GF/Speech/TransformCFG.hs
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@@ -89,9 +89,17 @@ stateGFCC = mkGFCC . mkCanon2gfcc . stateGrammarST
-- * Grammar filtering -- * Grammar filtering
-- | Removes all directly and indirectly cyclic productions. -- | Removes all directly and indirectly cyclic productions.
-- FIXME: this may be too aggressive, only one production
-- needs to be removed to break a given cycle. But which
-- one should we pick?
-- FIXME: Does not (yet) remove productions which are cyclic
-- because of empty productions.
removeCycles :: CFRules -> CFRules removeCycles :: CFRules -> CFRules
removeCycles = groupProds . removeCycles_ . ungroupProds removeCycles = groupProds . f . ungroupProds
where removeCycles_ rs = [r | r@(CFRule c rhs _) <- rs, rhs /= [Cat c]] where f rs = filter (not . isCycle) rs
where alias = transitiveClosure $ mkRel [(c,c') | CFRule c [Cat c'] _ <- rs]
isCycle (CFRule c [Cat c'] _) = isRelatedTo alias c' c
isCycle _ = False
-- | Removes productions which use categories which have no productions. -- | Removes productions which use categories which have no productions.
-- Only does one pass through the grammar. -- Only does one pass through the grammar.