currently $var is only legal in an rvalue context; add some support for writing to target vars
It's actually somewhat hard to test this feature, but as far as I know it's now working. By "working" I mean: writing using operator =, to base types. No support for += or other op= forms at the moment, and no support for pointer types or strings.
Do the not-working parts behave like clean failures? Testsuite? Is guru mode enforced for $var lvalue operations?
The not-working parts fail as exceptions, yes. I've now predicated it on guru mode, and added testsuite/buildok/twenty.stp (previously I was hunting around for a test which would be safe to *run*, which is hard to find. most writing to the kernel is sort of dangerous!)
belated