Re: [Haskell-cafe] stream/bytestring questions

On Sun, 2008-02-17 at 18:02 -0800, Chad Scherrer wrote:

On Feb 17, 2008 5:01 PM, Don Stewart wrote:

...

yeah, with lists, as compared to bytestrings, there are:

* more complex operations to fuse * allocation is much cheaper (lazy list cons nodes) * built in desugaring for build/foldr fusion interferes (enumerations, comprehensions)

so the benefits of fusing lists are less obvious than bytestrings, where every fusion point knocks out a big array allocation, and they're a bit more complex to get the full api going.

Ok, that makes sense.

...

no, using the rules should be fine. you're not supposed to program in the stream abstraction.

I was working on some run-length encoding stuff and found it most natural to do a lot of it using unfoldr, and I had a state in the unfold that was naturally represented as a tuple. I got a little worried about all the packing and unpacking tuples not being optimized out, and this got me wondering about just using Streams directly. At the time, the Skip constructor for a Step felt natural to use in some places, which I thought could be really convenient. I dunno, maybe it's not an issue. Hmm, if it would help I can try to post some of the code...

It's -quite- possible that a coalgebraic perspective is much more natural for your code/problem. If that's the case, use it (the coalgebraic perspective that is). Obviously depending on the internals of the stream library is not a good idea and using Streams directly was not their intent, but it is your code. Do what you will.