Applicative and parsec3

[Edward Kmett]

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

On Fri, Jan 28, 2011 at 8:57 AM, Christian Maeder
<Christian.Maeder at dfki.de>wrote:

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