Hackathon: Lens does not permit result branching

[AndrewSisley]

Some operations can return two different answers, e.g. x^(0.5) - given 4, this could be either 2 or -2.

It may be highly desirable for each option to remain separate in its flow though the pipeline, allowing the pipeline to maintain their separation all the way through and return multiple sets of answers:

            => f
a => b => d => g
  => c => e => h
            => i

[AndrewSisley]

Some form of tracing may be desirable here, and the ability to discard unwanted variants (e.g. if external knowledge determines that the result cannot be negative then future processing of that result-variant can be skipped)