Luke Palmer wrote:
Heinrich Apfelmus wrote:
Conal Elliott wrote:
For anyone interested in iteratees (etc) and not yet on the iteratees mailing list.
I'm asking about what iteratees *mean* (denote), independent of the various implementations.
In my world view, iteratees are just a monad M with a single operation
symbol :: M Char
that reads the next symbol from an input stream.
So perhaps this could be a reasonable semantics?
Iteratee a = [Char] -> Maybe (a, [Char]) = MaybeT (State [Char]) a
symbol [] = Nothing symbol (c:cs) = Just (c, cs)
I'm not experienced with iteratees. Does this miss something?
From a purely denotational point of view, that's a reasonable semantics. However, and that's the main point, with this particular semantics, it is impossible to implement runHandle :: M a -> Handle -> IO a without using unsafeInterleaveIO . Typical implementations of iteratees do make that possible, by being able to suspend the iteratee after feeding it a character. There are also enumerators and enumeratees. I think that purpose of enumerator = run an iteratee on multiple sources (i.e. first part of the input from a Handle , second part from a String ) purpose of enumeratee = iteratee as a stream transformer, i.e. as a map [x] -> [y] I am not sure whether this elaborate reinvention of the standard lists functions is worth the trouble. Regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com