Re: [tlaplus] Converting TLA+ spec to PlusCal

[Deividas Bražėnas <deividas.brazenas@xxxxxxxxx>]

Thank you, Stephan!!

I'm also wondering how I could write the following in PlusCal.

I have these global variables:

peers = {n_1, n_2, n_3, n_4}

msgs = [node_id \in peers |-> {}]

I want to add [t |-> "PROPOSE"] message for every peer in a process.

I've tried to do it like this, but it does not work as expected. What may I be doing wrong?

        print <<"with">>;

        with peer_id \in peers do

            print <<"peers", peers, "peer", peer_id>>;

            msgs[peer_id] := msgs[peer_id] \union {[t |-> "PROPOSE"]};

        end with;

        print <<"msgs", msgs>>;

I get the following output:

<<"with">>

<<"peers", {n_1, n_2, n_3, n_4}, "peer", n_1>>

<<"msgs", (n_1 :> {[t |-> "PROPOSE"]} @@ n_2 :> {} @@ n_3 :> {} @@ n_4 :> {})>>

<<"peers", {n_1, n_2, n_3, n_4}, "peer", n_2>>

<<"msgs", (n_1 :> {} @@ n_2 :> {[t |-> "PROPOSE"]} @@ n_3 :> {} @@ n_4 :> {})>>

<<"peers", {n_1, n_2, n_3, n_4}, "peer", n_3>>

<<"msgs", (n_1 :> {} @@ n_2 :> {} @@ n_3 :> {[t |-> "PROPOSE"]} @@ n_4 :> {})>>

<<"peers", {n_1, n_2, n_3, n_4}, "peer", n_4>>

<<"msgs", (n_1 :> {} @@ n_2 :> {} @@ n_3 :> {} @@ n_4 :> {[t |-> "PROPOSE"]})>>

Where I would expect:

<<"with">>

<<"peers", {n_1, n_2, n_3, n_4}, "peer", n_1>>

<<"peers", {n_1, n_2, n_3, n_4}, "peer", n_2>>

<<"peers", {n_1, n_2, n_3, n_4}, "peer", n_3>>

<<"peers", {n_1, n_2, n_3, n_4}, "peer", n_4>>

<<"msgs", (n_1 :> {[t |-> "PROPOSE"]} @@ n_2 :>  {[t |-> "PROPOSE"]}   @@ n_3 :>  {[t |-> "PROPOSE"]}   @@ n_4 :>  {[t |-> "PROPOSE"]}  )>>

On Monday, December 19, 2022 at 8:30:20 AM UTC+2 Stephan Merz wrote:

Hello,

TLA+ is more general than PlusCal, and a systematic conversion to PlusCal is unlikely to yield idiomatic results, if it is possible at all: you will probably end up with a single while loop containing all possible actions. It is a bit like the normal form theorem in computability theory.

On 18 Dec 2022, at 13:24, Deividas Bražėnas <deividas...@xxxxxxxxx> wrote:

Hello all,

I have a TLA+ spec that I'd like to convert to PlusCal, but I'm facing some issues as I don't know how to convert a few parts of the specification.

1. I want to have this predicate as a process, but I'm not sure how to convert this part "\E n \in CN, p \in BOOLEAN :"

UpdatePredicate ==

\E n \in CN, p \in BOOLEAN :

/\ predicate[n] => p \* Only monotonic updates are make the algorithm to terminate.

/\ predicate' = [predicate EXCEPT ![n] = p]

/\ UNCHANGED <<bcNode, bcValue, output, msgs>>

In PlusCal you could represent this as

with (n \in CN, p \in BOOLEAN) {

  await (predicate[n] => p);

  predicate[n] := p

}

2. I want to specify global variable bcValue in Init based on the set of bcNode

/\ \/ bcNode \in CN /\ bcValue \in Value

    \/ bcNode \in FN /\ bcValue = NotValue

You could perhaps write

variables

  bcNode \in CN \union FN,

  bcValue \in (CASE bcNode \in CN -> Value [] bcNode \in FN -> {NotValue});

Stephan

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