[Haskell-cafe] parsec3 pre-release [attempt 2]

Antoine Latter aslatter at gmail.com
Sat Feb 2 18:28:07 EST 2008

I'm not a fan of parameterizing the "Stream" class over the monad parameter `m':

> class Stream s m t | s -> t where
>    uncons :: s -> m (Maybe (t,s))

which leads to instance declarations like so:

> instance Monad m => Stream [tok] m tok where
>     uncons []     = return $ Nothing
>     uncons (t:ts) = return $ Just (t,ts)

I looked through the sources and I didn't see anywhere where this
parameterization gained anything.  As a proof of this I did a
mechanical re-write removing the class parameter, and the library
still seems to work.


On Feb 1, 2008 11:15 PM, Derek Elkins <derek.a.elkins at gmail.com> wrote:
> [Now with 100% more correct darcs get URLs.]
> I'm currently getting Paolo Martini's Google Summer of Code project, an
> updated version of Parsec, into a releasable state, and I will be
> maintaining it for at least a while.
> Paolo's major additions are:
>     * The Parser monad has been generalized into a Parser monad
>       transformer
>     * The parsers have been generalized to work over a stream of any
>       type, in particular, with bytestrings.
> I have made a few minor additions as well:
>     * There is Haddock documentation for almost all functions
>     * The Parser monad now has Applicative/Alternative instances
> Currently, I am looking for people to give it a go reporting any bugs in
> the library or documentation, troubles building it, or changes/features
> they would like.  I'm also interested in performance information.
> Most old Parsec code should be relatively easy but not trivial to port.
> There is a darcs repository on code.haskell.org.  If nothing comes up,
> I'll put a package on Hackage in about a week or so.
> To get the code:
> darcs get http://code.haskell.org/parsec3
> To build it, the standard cabal commands should work:
> http://haskell.org/haskellwiki/Cabal/How_to_install_a_Cabal_package
> Alternatively, you can use the cabal-install application:
> http://hackage.haskell.org/trac/hackage/wiki/CabalInstall
> The documentation can be generated also via the normal cabal routine, or
> via cabal-install.
> The Text.Parsec modules should be preferred to the
> Text.ParserCombinators.Parsec modules.
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