Re: PROPOSAL: Some more 'Applicative' combinators

Hello, Sorry, I should have mentioned the origin of the combinators. These are (generalizations of) standard parser combinators, so think of "f a" in the type as a parser that can construct values of type "a". With this in mind, it should be more obvious what these combinators are used for. For example:

p `sepBy` sep is a parser that will return 0 or more occurances of 'p' separated by 'sep'. Many (all?) parser combinator libraries provide these functions, so having the generic 'Alternative' interface makes it easier to write parser that can work with different libraries. -Iavor

On Jan 6, 2008 3:34 PM, Seth Kurtzberg wrote:

Can you show some code fragments demonstrating how the combinators are used? I find it easier to understand the underlying concepts when I have not only the signature and implementation but an example of a typical use. It doesn't have to be working code, and it might even be pseudo code. (I'm not sure whether other Haskell folks feel the same way.)

On Sun, 6 Jan 2008 13:35:41 -0800 "Iavor Diatchki" wrote:

...

Hello, I propose that we add the following combinators to the 'Control.Applicative' module:

skipMany :: (Alternative f) => f a -> f () skipMany p = skipSome p <|> pure ()

skipSome :: (Alternative f) => f a -> f () skipSome p = p *> skipMany p

endBy :: (Alternative f) => f a -> f b -> f [a] endBy p s = many (p <* s)

endBy1 :: (Alternative f) => f a -> f b -> f [a] endBy1 p s = some (p <* s)

sepBy :: (Alternative f) => f a -> f v -> f [a] sepBy p s = sepBy1 p s <|> pure []

sepBy1 :: (Alternative f) => f a -> f v -> f [a] sepBy1 p s = (:) <$> p <*> many (s *> p)

Any objections? Deadline for discussion is 2 weeks from now, which would be the 20th of Jan.

-Iavor _______________________________________________ Libraries mailing list Libraries@haskell.org http://www.haskell.org/mailman/listinfo/libraries

-- Seth Kurtzberg Hardware/Software/Driver Engineering