all control flow should be accomplishable by three instructions:

allocate
copy
send

Allocate takes two arguments: type (an rvalue), and result (an
lvalue).  It verifies that type is a Class, fetches the number of
slots required for that Class, and allocates that many slots of
storage.  It places a reference to the new storage in result.
Allocate will only accept a small fixed set of type values.  It
probably also needs a size argument so it can allocate arbitrary sized
messages.

Copy takes two arguments:  from (an rvalue), and to (an lvalue).  It
makes a copy of the reference in from and places it in to.

Send takes one argument:  message (an rvalue).  It verifies that
message is a Message, extracts the target and invokes the target's
dispatcher on the Message.

All other operations are side effects of particular message sends.

An rvalue is either a slot reference, or an immediate value (provided
by the loader).

An lvalue is a slot reference.

The current execution has a reference to the current execution
context.  That context is at depth zero.  Each context has a reference
to the parent context, which is at one higher depth than itself.  A
slot reference is a depth and an offest into the context at that
depth.  A depth of -1 indicates the message which initiated the
current execution.  The parent pointer can't be set by a copy; it has
to be set automatically by allocate.