[dndqwieb] Nondeterministic COME FROM

Consider an evil programming language with COME FROM as the only jump instruction, made famous in the response to Go To Statement Considered Harmful.

If two ComeFroms have the same source, they execute nondeterministically in parallel until one of them encounters a Fail statement.

The only control structure (branch) is IF test THEN FAIL.

Of course, for maximum evilness, we permit, encourage even, "computed" ComeFrom, in which the origin of the Come From is not known until run time.