On 9/24/10 1:45 PM, Thomas Schilling wrote:
Regarding the questions: I prefer the foldr/l names, because otherwise I may need to look up the documentation to figure out which fold it is. It's much better to use the standard naming convention from lists. As an example, there is foldM which is actually a left fold. Data.Foldable fixes this and only uses the generic name 'fold' for the Monoid case where order does indeed not matter due to associativity of mappend.
I agree with both parts of this. That is, foldr/l are the best names for when the order is specified. However, sometimes we do have an associative operator and don't care about the order. In these latter cases I think it's best to offer a "fold" which doesn't specify order in order to prevent client code from over-specifying what they mean. Also, having an order-independent fold allows the library to choose whatever kind of fold would be most efficient (possibly changing it over time), and allows for things like a parallel implementation for overcoming the "fold considered harmful"[1] problem. [1] http://vidiowiki.com/watch/p92te4e/Guy_Steele_foldl_and_foldr_considered_sli... -- Live well, ~wren