On Oct 31, 2010, at 17:15 , Nils Schweinsberg wrote:
Am 31.10.2010 16:53, schrieb Vo Minh Thu:
I can't really tell from your description, but maybe this is because of the way Parsec works when it deals with alternatives. When you combine several parsers with e.g. '<|>' or 'choice', an alternative that can consume some input but fails will make the whole combined parser fail too. So you have to either factorize you parsers or use the 'try'. See the documentation for 'try' at http://hackage.haskell.org/packages/archive/parsec/3.1.0/doc/html/Text-Parse... .
This is exactly what gives me headaches. It's hard to tell where you need try/lookAhead and where you don't need them. And I don't really feel comfortable wrapping everything into try blocks...
This is precisely why you should use a more general parser library like uu-parsing and try to avoid the more low-level techniques used in Parsec; uu-parsinglib avoids all the confusion arising from the use of try constructs. It furthermore gives you an online result, error correction and nice error messages. Its Utils module contains a lot of useful "standards" elements you might want to recognise. Thus far i have only happy users, and if you are having any problems please let me know. Doaitse PS: for all parsing libraries it holds that parsing times are negligeable when compared to the time spent on what you want to do with the parsed result.
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