ops typo
ex 5.18 - two approaches explained
ex 5.18 - make-register redo
ex 5.18 - reg helpers
ex 5.18 - register test run without machine
ex 5.18 - legacy - add primitive
ex 5.18 - legacy - primitive fix
ex 5.18 - working example
ex 5.18 - split controller
ex 5.18 - put some description words
ex 5.18 - patch impl
ex 5.18 - empty machine dry run. fix impl
ex 5.18 - expose operations to the machine
ex 5.18 - test pretty print
ex 5.18 - simu - not a working solution
ex 5.18 - plan changed

I find my second approach is far more complicated
than I have expected. So go back to the approach
suggested by the exercise instead.
ex 5.18 - re-impl
ex 5.18 - done