Collections design issues

Consider implementing in a unified stream/collection framework

• want side-effect-free operations for the lazy/infinite version
  • lazy/infinite stream version doesn't have size(), reduce(), etc.

Consider adding contains, get, find to type Collection

Consider a mutable "collect" operation similar to Java's

• also variants of reduce, e.g. with no identity value but returning an option, or a parallelizable version that takes an identity, an accumulator, and a combiner