Chunked Enumerable revisited (in F#)

Revisiting an old post on the subject, prompted by a recent question on the MSDN Visual F# forum.

Despite it being a very common thing to want to do, to process a stream of data in blocks, there isn't a library function for it yet; and it's not something that can be put together in a functional form using the pieces we have in the Collections.Seq module. Either, as in my earlier attempts, we have to go into object-land, with intrusions into the implementation details of enumerations (and their disposal), and eager evaluation at best; or we have to go imperative/procedural to get full lazy evaluation as per the code buried within the this C# example.

For idiomatic F#, we don't want an extension method, but a stand-alone function which we can chain into the usual pipeline of |> operations, so we would translate it thus —

where we bury the imperative/mutable kernel, the place where we count the number of steps we take (or stop early when we hit the end of the input), inside an inner function.