Don Stewart wrote:
You'd want a general fusion framework for this... Stream fusion... at least does this for zips... but for an arbitrary 'f' instead of zip, seems harder.
And of course, you wouldn't want that: f xs = xs : map expensiveCalculation xs Please don't fuse those two loops into one. In the case of "mean", the outer function in question is /, and that is a good candidate for fusion because it is strict in both arguments. I think Don is right. There is a lot of room for expanding the scope of fusion, but it needs to be done one function at a time until our strictness analysis gets better. In the general case, I like the way things work now. The original complaint about "unpredictability" is, in my opinion, a "bug in the documentation". This is yet another concept whose basics need to be made much more accessible to newbies. -Yitz