On 3/27/11 9:58 PM, John Millikin wrote:
Resending is slightly more complex -- if the other end can say "resend that last chunk", then it should be easy enough, but "resend the last 2 bytes of that chunk you sent 5 minutes ago" would be much harder. What is your use case?
This does highlight one of the restrictions I've lamented about the iteratee framework. Namely that the current versions I've seen place unnecessary limitations on the communication the iteratee is allowed to give to the enumerator/enumeratees above it. This is often conflated with the iteratee throwing an error/exception, which is wrong because we should distinguish between bad program states and argument passing. Moreover the type system doesn't capture the kinds of communication iteratees assume of their enumerators/enumeratees, nor the kinds of communication supported by the enumerators/enumeratees, which means that failure to hook them up in the right (non-typechecked) way /does/ constitute an error.
The one example that tends to be supported is the iteratee requesting that the enumerator/enumeratees seek to a given position in a file. Which is a good example, but it's not the only one. Requesting the resending of chunks is another good example. But there's no limit to the reasonable kinds of communication an iteratee could want.
In an ideal framework the producers, transformers, and consumers of stream data would have a type parameter indicating the up-stream communication they support or require (in addition to the type parameters for stream type, result type, and side-effect type). That way clients can just define an ADT for their communication protocol, and be done with it. There may still be issues with the Expression Problem, but at least those are pushed out of the stream processing framework itself which really shouldn't care about the types of communication used.
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