2009/5/13 Don Stewart
rl:
On 12/05/2009, at 14:45, Reiner Pope wrote:
The Stream datatype seems to be much better suited to representing loops than the list datatype is. So, instead of programming with the lists, why don't we just use the Stream datatype directly?
I think the main reason is that streams don't store data and therefore don't support sharing. That is, in
let xs = map f ys in (sum xs, product xs)
the elements of xs will be computed once if it is a list but twice if it is a stream.
The other issue is reminding developers to preserve stream invariants, so as not to break the heavy duty rewriting that's going to happen to their code.
Can you elaborate on this please? I've only seen a few invariants mentioned when reading the Stream Fusion paper and the stream-fusion source code. They are: 1. 'Skip' values should have no semantic significance. 2. Don't construct bottom Streams. However, this seems to only apply when the fusion rewrite rule is applied, which is not the case I am talking about. Cheers, Reiner