Compiler: ignore objects

[josephjclark]

A good optimisation in the compiler would be to ignore structures like objects, which we don't really do anything with.

Parsing large JSON objects is very intensive for the compiler.

What we'd ideally do is make the visitor quit when it starts traversing a structure like an object.

Counter point: we do need to support lazy state in object properties. Oh but not in a callback. So in some places yeah, we might be able to exit early.