[Haskell-cafe] A valuable new combinator for Parsec?

Tomasz Zielonka tomasz.zielonka at gmail.com
Mon Mar 12 07:33:54 EDT 2007

On Mon, Mar 12, 2007 at 11:24:48AM +0100, Maxime Henrion wrote:
> While using the very nice "option" combinator of Parsec recently, it
> seemed to me that it would be useful to have a more specific kind of
> combinator for optional tokens that wraps the token into a Maybe type.
> So, that gives:
> pmaybe :: GenParser tok st a -> GenParser tok st (Maybe a)
> pmaybe p = option Nothing (p >>= return . Just)
> I've been using it happily with some code of mine.  Do people think
> that it would be generally useful to have in Parsec?

Yes, it would certainly be useful. I think "optional" should work this
way, but unfortunately it returns ().


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