Re: Applicative and parsec3

On Fri, Jan 28, 2011 at 10:59 AM, Antoine Latter wrote:

On Fri, Jan 28, 2011 at 10:52 AM, Edward Kmett wrote:

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While you're hacking around on parsec a nice improvement would be to relax the type on the language generators in Text.ParserCombinators.Parsec.Language. (This one could be done without so drastic a change as bumping from 3 to 4): They can all be instantiated for Monad m => GenLanguageDef String s m instead of LanguageDef, this would greatly extend their usability. You could even go a little farther and relax them so they can work over Bytestrings, etc. I for one always feel a little twinge when I'm forced to copy and paste them and change the signature just because I'm working in a parser that provides state, uses _any_ base monad, or consumes some other Char source. -Edward Kmett

I'd be happy to apply a patch for this.

To be more clear, to the 'parsec' package. I think Christian would have to do it for the new 'parsec3' package. Antoine

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On Fri, Jan 28, 2011 at 8:57 AM, Christian Maeder wrote:

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Am 27.01.2011 07:16, schrieb Kazu Yamamoto (山本和彦):

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Hello,

I'm using parsec3 with the applicative style. Since the functions in Control.Applicative and parsec3 conflicts, I need to use the "hiding" keyword as follows:

      import Control.Applicative hiding (many,optional,(<|>))       import Text.Parsec

This is inconvenient for me. I would like to use them as follows:

      import Control.Applicative       import Text.Parsec

Christian, the maintainer of parsec3, told me that it is possible to use the functions of Control.Applicative in parsec3 instead of implementing its own functions. But (<|>) of parsec3 is "infixr 1" while that of Control.Applicative is "infixl 3".  This may be an issue.

Any ideas to solve this issue?

If parsec is not changed I could create a parsec4 package where the conflicting functions are removed from Text.Parsec.

This will break code that uses "optional" from Text.Parsec. Is there a need for a renaming of Text.Parsec.Combinator.optional, like "voidOptional"?

Such a function would be better placed inside Control.Applicative though:

 voidOptional v = const () <$> v <|> pure ()

or

 voidOptional = void . optional

using the new Control.Monad.void.

C.

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--Kazu

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