Neil Mitchell schrieb:
Hi,
I'm using parsec to parse something which is either a "name" or a "type". The particular test string I'm using is a type, but isn't a name. I want things to default to "name" before "type".
Some examples of the parsec function, and the result when applied to a test string:
parsecQuery = do spaces ; types Right Query {scope = [], names = [], typeSig = Just [a], items = [], flags = []}
parsecQuery = do spaces ; names Left (line 1, column 1): unexpected "[" expecting white space, "--", "/", "(", letter, "::" or end of input
parsecQuery = do spaces ; try names <|> types Left (line 1, column 1): unexpected "[" expecting white space, "--", "/", "(", letter, "::" or end of input
I would have expected try names <|> types to return a Right (since types matches), but it doesn't. I assumed this would be a property of Parsec, but it doesn't appear to hold. Can anyone shed any light?
I suppose "names" or "try names" succeeds without consuming input, but calling parsecQuery fails for another reason that you haven't shown, C.