Re: [tlaplus] Beginner question: EXCEPT construct

Hello,

if my understanding is correct, you would like to update the function state for all elements of the set. There is no specific syntax for this, write

state' = [ x \in DOMAIN state |-> IF x \in A THEN "newState" ELSE state[x] ]

(Presumably you can replace "DOMAIN state" by a simpler set.)

Hope this helps,

Stephan

On 2 May 2019, at 10:38, kestutis@xxxxxxxxx wrote:

Suppose the next state relation for the function "state" is:

state' = [state EXCEPT ![A] = "newState"]

where A is some argument of the function "state". This obviously works when A is a single argument.

What about when A is a "set of arguments" (i.e., A = {"A1", "A2", "A3"})? Then the _expression_:

state' = [state EXCEPT ![A] = "newState"]

is not correct: TLC gives an error message:

"TLC threw an unexpected exception.
This was probably caused by an error in the spec or model. See the User Output or TLC Console for clues to what happened. The exception was a java.lang.RuntimeException: Attempted to check equality of string "A1" with non-string: {"A1"}

The error occurred when TLC was evaluating the nested
expressions at the following positions:"

Clearly, I am missing something obvious. How could it be possible to resolve this?

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