Exception transparency

[Nathan Bryant]

Brian Goetz wrote:

> Consider a method like List.forEach().  If forEach() has to assume the
worst 
> (impurity), then forEach() must be sequential.  But that is terrible!
Adding 
> closures and not allowing the possibility of parallel iteration?  Not
OK.

A nice idea but not workable. Sometimes we really do want to parallelize
things that either affect shared state, perform I/O, or both. Such
operations can frequently encapsulate the state in such a way that they
are -relatively- pure, but adding static type checking of such
"relative" pureness is not going to be workable at least not in a way
that the average programmer can understand.

Views are the way:

Iterable.par().forEach()
Iterable.seq().forEach()