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Re: [tlaplus] How do you do functions of structures?

On 06.06.21 15:57, Isaac DeFrain wrote:

To manage the amount of names I have to write following UNCHANGED, I usually write several /inclusive/ and /exclusive/ variable tuples; e.g. say we have the variables x1, x2, ..., xN and I have a few actions which change only x1 and x2 and leave x3, ..., xN unchanged (this would suggest an exclusive variable tuple to me). I'll define a tuple, call it non_x1_x2_vars == <<x3, ..., xN>>, and then just write UNCHANGED non_x1_x2_vars in the aforementioned actions. As long as you write all your actions in one module, this seems to work really well. Not to mention when you have 10+ variables in a spec, it becomes next to impossible to visually inspect whether you have included all the unchanged variables.

I first saw this little trick in the raft spec <https://github.com/ongardie/raft.tla/blob/master/raft.tla> where they use several (what I would call) inclusive variable tuples.


have you tried *simulating* the specs with TLC for a few seconds to find any missing variables in UNCHANGED statements? I haven't yet, but I would expect the trick to catch most of them.


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