The contents of a cell may be null, just like any other local.
We should report this as an error.
So that we can name the variable in the error message,
we change the instruction set so that LOCAL<local>+CELL
are combined into a single LOCALCELL<local> instruction,
and FREE<free>+CELL become a single FREECELL<free> instruction.
For symmetry we also combine LOCAL<local>+SETCELL into SETLOCALCELL,
though it cannot fail. (Happily, all three changes are optimizations
previously described by TODO comments.)
The contents of a cell may be null, just like any other local. We should report this as an error.
So that we can name the variable in the error message, we change the instruction set so that
LOCAL<local>+CELLare combined into a singleLOCALCELL<local>instruction, andFREE<free>+CELLbecome a singleFREECELL<free>instruction. For symmetry we also combineLOCAL<local>+SETCELLintoSETLOCALCELL, though it cannot fail. (Happily, all three changes are optimizations previously described by TODO comments.)Fixes #340