Is there any follow up on this? I was wondering what is the best way to sequence a number of sources together. Anybody gave a further thought on this?
Regards, Paul Liu On Tue, Dec 27, 2011 at 3:45 PM, Aristid Breitkreuz <arist...@googlemail.com> wrote: > Hi all, > > As you may have noticed, Michael Snoyman has been working on an > alternative approach to I/O, called conduits. You can find it here: > > https://github.com/snoyberg/conduit > > When looking at the Source type (explained here: > http://www.yesodweb.com/blog/2011/12/conduits), I noticed that they > seem to behave "like lists", and naturally wondered if I could write a > Monad instance for them. But first, let's have a brief look at the > definition of Source: > > data SourceResult a = Open a | Closed > > data PreparedSource m a = PreparedSource > { sourcePull :: ResourceT m (SourceResult a) > , sourceClose :: ResourceT m () > } > > newtype Source m a = Source { prepareSource :: ResourceT m > (PreparedSource m a) } > > ResourceT deals with resource acquisition and releasing (making sure > that all resources are released), and provides a an abstraction over > IORef/STRef. For our purposes here, ResourceT is probably close enough > to IO. > > > So now the question again is, can we write a Monad instance for this? > I have been able to write join (concatenate) and return (a source with > a single non-repeated) element. > > https://gist.github.com/1525471 > > I _think_ it behaves properly like a Monad, but I'm not quite sure, > and neither was Michael. Greg Weber then suggested bringing the > question to this forum. What made the question difficult for me is > that this would be a stateful Monad transformer, so I'm not quite sure > how to test the Monad laws properly. > > > There's a second part to this question: If Source turns out not to be > a Monad, is it possibly a ZipList-like Applicative? And either way, > which is more useful: The list-like or the ziplist-like instances (of > Applicative/Monad)? > > > > Thank you, > > Aristid > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe -- Regards, Paul Liu _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
