- extend the VM interrupts to distinguish between read and write
events
- add new ADD-PENDING-CHANNEL instruction to the VM
- add WAIT-FOR-CHANNELS procedure to the run-time system
- implement SELECT and SELECT! on top of that in newports.scm
This runs some basic tests, but in general should be considered
largely untested.
Moreover, SELECT/SELECT! never detect any exceptional conditions---the
returned vectors are always empty. This is because the VM doesn't
really track those, and it's unclear whether it would be worth the
effort.
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