FS: Parsec as a monad transformer

The proposed Parsec3 package for Haskell has Parsec implemented as a monad transformer, which means I can do things like:


> data MyType
>     = Foo
>     | Baz
>     | Err
>  deriving Show


> parseMyType = (string "Foo" >> return Foo)
>           <|> (string "Baz" >> return Baz)


> parseNoBaz = callCC $ \k -> do
>                result <- parseMyType
>                validateResult k result
>                return result


> validateResult k Baz = k Err
> validateResult k _ = return ()


> manyNoBaz = parseNoBaz `sepBy` space


> test p s = flip runCont id (runPT p () "test" s)

Then, if I execute test manyNoBaz "Foo Foo Baz Foo" I get the result:


[Foo,Foo,Err,Foo]

This is a contrived example, but I think it's pretty neat.

FS