pure functions and the parallel evaluation of reduce-like operations

[Brian Goetz]

> Do we define annotations to declare intent (e.g, @Associative)?  Do we have
> multiple reduce operations (e.g., leftReduce, rightReduce,
> associativeReduce, unorderedReduce)?  Do we pass in the function's
> constraints as a parameter (e.g., List.reduce(Operation.ASSOCIATIVE, #{s v
> -> s + v}))?

This sort of thing would be a good match for Mike Ernst's work on pluggable type systems via JSR 308 and the "checkers" framework.