[Haskell-cafe] Fwd: Semantics of iteratees, enumerators, enumeratees?

John Lato jwlato at gmail.com
Tue Aug 24 08:00:30 EDT 2010

> From: "C. McCann" <cam at uptoisomorphism.net>
> What sets an iteratee-style design apart from something conventional
> based on a State monad is that the iteratee conceals its internal
> state completely (in fact, there's no reason an iteratee even has to
> be the "same" function step-to-step, or have a single consistent
> "state" type--almost has an existential flavor, really), but is at
> another function's mercy when it comes to actually doing anything.
> All of which doesn't really shed too much light on the denotation of
> these things, I suppose, as there's barely anything there to talk
> about; the iteratee automaton itself is a terribly simple construct,
> relying on an underlying monad to perform actions, on an external
> "push" data source to recurse, and being given only bite-size chunks
> of data at each step. It's little more than foldl with a "pause"
> button attached.

This is how I think of them.  I particularly your description of them as a
foldl with a "pause" button.

Maybe it would be helpful to consider iteratees along with delimited

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