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Simplify the chain for choices.

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This commit is contained in:
Rob Rix 2017-07-22 14:56:19 -04:00
parent f628d22aee
commit 40313b598f
1 changed files with 1 additions and 1 deletions
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src/Data/Syntax/Assignment.hs
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@ -261,7 +261,7 @@ runAssignment toNode source assignment state = go assignment state >>= requireEx
Children childAssignment | node : _ <- stateNodes state -> do
(a, state') <- go childAssignment state { stateNodes = toList (F.project node) } >>= requireExhaustive
yield a (advanceState state' { stateNodes = stateNodes state })
Choose choices | Node symbol _ _ : _ <- toNode . F.project <$> stateNodes state, Just a <- IntMap.lookup (fromEnum symbol) choices -> yield a state
Choose choices | Just choice <- flip IntMap.lookup choices . fromEnum . nodeSymbol . toNode . F.project =<< listToMaybe (stateNodes state) -> yield choice state
Many rule -> uncurry yield (runMany rule state)
-- Nullability: some rules, e.g. @pure a@ and @many a@, should match at the end of input. Either side of an alternation may be nullable, ergo Alt can match at the end of input.
Alt a b -> either (yield b . setStateError state . Just) Right (yield a state)