_CALL_DIRECT, GOTO_DIRECT with auto-link

[xparq]

The arg. is a direct C++ RULE obj. address, which is auto-linked across object copy/move events via a _from chain (map) built by the ctors... (Copy ctors update the target for _from to this, and also create 1 new entry for the source obj, setting it also to this; move ctors just update the target for _from: links[_from] = this)

During execution, when a direct address arg is found, it's original value is looked up (as a key in the links map), and replaced with the final address. If the link is not found, it's an error (and the instruction is aborted (-> "kinda exceptions")).

And then, to prevent subsequent redundant lookups (the exact reason why _DIRECT adressing exist in addition to named references), the instruction opcodes themselves are replaced with their ..._RESOLVED counterparts...

Note: this precludes the entire syntax rule tree ("program") from being const! But then it at least opens the door for constructing rules run-time! Or... it means compilation (#31; as already mentioned in #15) -- which, then OTOH, would kinda prevent dynamically modifying/creating grammar then...

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This suggest the usual technique of allocating bits of the opcode for encoding the addressing mode, to allow generalizing it to any instructions.