[Haskell-cafe] ANNOUNCE: pipes-core 0.1.0
Twan van Laarhoven
twanvl at gmail.com
Tue Apr 10 17:50:07 CEST 2012
On 09/04/12 23:49, Paolo Capriotti wrote:
> I'm pleased to announce the release of version 0.1.0 of pipes-core, a
> library for efficient, safe and compositional IO, similar in scope to
> iteratee and conduits.
>
> http://hackage.haskell.org/package/pipes-core
>
I have some issues with the function names used
firstP :: Monad m => Pipe a b m r
-> Pipe (Either a c) (Either b c) m r
secondP :: Monad m => Pipe a b m r
-> Pipe (Either c a) (Either c b) m r
Why are firstP and secondP not called leftP and rightP? Those are the
corresponding functions in Arrow. Similarly (***) should be called (+++).
I also don't like `intersperse`, which does something completely
different from its Data.List counterpart.
intersperse :: Monad m => (a -> Bool) -> Pipe a (Maybe a) m r
Data.List.intersperse :: a -> [a] -> [a]
The documentation is also a bit misleading "Yield Nothing when an input
satisfying the predicate is received." To me this suggests that could
behave like some kind of filter,
intersperse p = pipe $ \x -> if p x then Nothing else Just x
A true intersperse analogue would be
intersperse x = do
y0 <- await
yield y0
forever $ do
y <- await
yield x
yield y
The function you have defined is something like
`yieldNothingBeforeMatching`. Do you have a use case for this function?
Perhaps an interesting combinator would be
-- | Run the first pipe until it yields a value, then run the
second pipe until it yields, the the first pipe again, etc.
alternate :: Pipe a b m r -> Pipe a b m r -> Pipe a b m r
intersperse x = alternate idP (forever (yield x))
Although I have no idea if it is actually useful in practice.
Twan
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