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Use Either’s MonadError instance to backtrack.

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This commit is contained in:
Rob Rix 2017-07-22 16:59:38 -04:00
parent 6caaec8289
commit 2adf4ee765
1 changed files with 2 additions and 2 deletions
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src/Data/Syntax/Assignment.hs
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@ -256,9 +256,9 @@ runAssignment toNode source assignment state = go assignment state >>= requireEx
atEnd nodeError = case assignment of
Location -> yield (Info.Range (stateOffset state) (stateOffset state) :. Info.Span (statePos state) (statePos state) :. Nil) state
Many rule -> uncurry yield (runMany rule state)
Alt a b -> either (yield b . setStateError state . Just) Right (yield a state)
Alt a b -> yield a state `catchError` (yield b . setStateError state . Just)
Throw e -> Left e
Catch during handler -> either (flip yield state . handler) Right (yield during state)
Catch during handler -> yield during state `catchError` (flip yield state . handler)
_ -> Left (fromMaybe (Error (statePos state) expectedSymbols Nothing) nodeError)
state | not (null expectedSymbols), all ((== Regular) . symbolType) expectedSymbols = dropAnonymous initialState