Proposal: Add a few extra members to Foldable and Traversable classes

Henning Thielemann lemming at
Fri Sep 19 20:29:31 UTC 2014

On Fri, 19 Sep 2014, Joachim Breitner wrote:

> Slightly off topic: Wouldn’t it be nice if we would not have to have to
> add these methods to provide optimized behavior, but rather have the
> user write "sum . toList" or some other idiomatic code (maybe suggested
> in the docs), and RULES provided by the container implementer would
> reliable replace this with the optimized version. Wouldn’t help in
> polymorphic code, but I doubt that much performance critical code is
> polymorphic in the container.
> But then he could simply provide a sumTree or sumSet or something
> else... I should stop mumbling in circles.

I am also worried about extending the classes more and more. Where to 
stop? At which point the API will be stable? A way to optimize non-methods 
for certain instances would be nice. Unfortunately, it is not only hard to 
predict when RULES fire, a RULES based solution is also dangerous. If a 
default method implementation and an actual instance implementation do 
different things, that's ok. In contrast, if a function is replaced by 
different functionality via RULES, that's very bad.

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