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Re: [tlaplus] Specifying an arbitrary function and then using it in TLC

Aha!  Thanks, Stephan; I had noticed when I evaluated CHOOSE in TLC it seemed to come up with the same function every time, but I had thought that in a "proper" simulation it behaved like \in and represented a state branch over all possibilities.  I should be set with whatever it picks, though (this is a bit of a toy problem in the sense that this round I'm mostly using TLA+ for the exercise of writing things down rather than exploring the state space, but your point on ASSUME is interesting; I hadn't thought of it and I confess don't think of using ASSUME much).

Hadn't noticed the randomization module, Markus.  Thanks very much!


On Wednesday, November 25, 2020 at 1:55:18 PM UTC-5 Markus Alexander Kuppe wrote:
On 25.11.20 10:31, Stephan Merz wrote:
> CHOOSE is arbitrary but deterministic choice. In other words, with your
> definition, TLC will generate one function (likely a very trivial one,
> perhaps mapping every instruction of A to the same instruction of B) and
> explore the spec for that particular function. If you want to explore
> the spec for every possible function, make the mapping a variable of
> your spec, add
> translateFn \in [...]
> to the initial condition and UNCHANGED translateFn to all actions. And
> if you want to play with different hand-picked functions, add a CONSTANT
> TranslateFn to your module and write
> ASSUME TranslateFn \in [...]
> then you define the particular function in the model. What is the right
> way to go depends on whether you want to explore if your transpiler
> works for some fixed function, for all functions or for some specific ones.

With the new-ish Randomization module [1,2], you could trick TLC to
check a more "interesting" subset of all functions.


[2] https://lamport.azurewebsites.net/tla/inductive-invariant.pdf

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