Re: Dataflow and Comonads was Re: [Haskell-cafe] Monads in Scala, ...

On Sat, 2005-11-26 at 18:43 +0100, Shae Matijs Erisson wrote:

Greg Woodhouse writes:

...

Maybe this is a different topic, but exploring concurrency in Haskell is definitely on my "to do" list, but this is really a bit of a puzzle. One thing I've been thinking lately is that in functional programming the process is really the wrong abstraction (computation is reduction, not a sequence of steps performed in temporal order). But what is concurrency if their are no processes to "run" concurrently? I've beren thinking about action systems and non-determinism, but am unsure how the pieces really fit together.

Maybe dataflow languages like Lucid Synchrone, Esterel and Lustre? http://en.wikipedia.org/wiki/Dataflow_language http://en.wikipedia.org/wiki/Synchronous_programming_language

I also think dataflow is a very nice model for concurrency in pure functional languages. You might want to look at some of the work done by Edward Lee's group in the EE Dept. at Berkeley. They developed a generalization of dataflow called "token flow" which is quite nice. It became one of the basic models supported by their heterogeneous simulation systems, Ptolemy and Ptolemy II. I seem to recall that one student at a Texas university did a PhD thesis on dataflow for Haskell and then went to work on token flow in Lee's group. The one downside I found to using dataflow was that most software people seem to be uncomfortable with the lack of identifiable processes doing significant bits of work. I guess if they they're not floundering around in mutual exclusion, semaphores, deadlock detection and all the other manifestations of unmanaged complexity, they don't feel they've *accomplished* anything (BTW I grew up on Dijkstra, Hoare and Hanson, so I can get away with saying this :-). Interestingly enough, and perhaps obvious in retrospect, I often found hardware designers to be very comfortable with dataflow computations. Does anyone know whether much research has been done on using dataflow for concurrency in pure functional computation? How does it mesh with evaluation strategies? And, of course, the flip side: has anyone looked at re-examining real-world problems, conventionally handled with coordinating/communicating processes, as dataflow computations? The latter consideration may be the toughest to deal with. I was working on a project to handle PHY level communication algorithms with dataflow, and I had a great deal of difficulty with the comma-detect function of XAUI. I made some progress, but I never found a satisfactory solution. On the other hand, I did work out a fairly nice dataflow algorithm for CRC32. -- Bill Wood