{}:delete and {}:exists up to spec

[lizmat]

No description provided.

[pmichaud]

1. Instead of adding more "where 0" candidates, might it be better to simply change the existing candidates to be :$delete where ?$delete, and let it fall back naturally to other candidates on failure?
2. Similarly, even if we keep the extra candidates, I'd feel more comfortable testing boolean true/false than smart matching against numeric 0.

Pm

[pmichaud]

jnthn++ points out that there should be a bang (!) after the named argument, as in :$delete! where ?$delete. (I intended the bang to be there but forgot.)

There's a question as to whether "fallback" will work once .{} is implemented as a sub instead of a method.

Pm

[lizmat]

Looking forward to getting more feedback and or seeing these commits merged :-)