Re: [tlaplus] how to updating state and return in a definition

Hello,

if you remove the empty pair of parentheses, your definition is correct TLA+. It defines an operator whose effect it is to increment the state variable val and in can be used inside an action like so:

MyAction ==

/\ ...

/\ Calculate \* update variable val

/\ ...

There is no notion of "returning" an update of a variable.

If you'd rather compute a value that can be used within an _expression_ you can define

ValPlusOne == val + 1

and have something like

f' = [f EXCEPT ![p] = ValPlusOne]

for updating an array at a certain position.

Regards,

Stephan

On 15 May 2019, at 02:54, Balaji Arun <ba2669@xxxxxx> wrote:

I am trying to have a specification with a definition for Calculate()

module A:

VARIABLE val Calculate() == val' = val + 1 (*return [v: val] here*)

How do I return that val to whoever is calling it (even another module that instantiates module A)? Assuming multiple processes call Calculate concurrently.

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