| The two commas look wrong: this could be an error in the PlusCal translator. If you can confirm this, could you open a GitHub issue? Could you share the entire TLA+ module?
What happens if you write something like
with m = [t |-> "PROPOSE", v |-> input] do msgs := [p \in peers |-> @ \cup {m}] end with
Stephan
I'm also wondering, maybe it would be possible to do that in a more simpler way? e.g. something like this:
msgs := [peer_id \in peers |-> msgs[peer_id] \cup {[t |-> "PROPOSE", v |-> input]}];
But this one gives me a syntax error at first "|->" operator when generated to following TLA+: msgs' = [peer_id[self] \in peers[self] |-> msgs[peer_id[self]] \cup {[t |-> "PROPOSE", , v |-> input[self]]}] On Wednesday, December 21, 2022 at 10:37:01 AM UTC+2 Deividas Bražėnas wrote:
Thanks for the answer, Stephan!
You can rewrite your loop as follows:
while peers # {} do with p \in peers do msgs[p] := @ \union {...}; peers := peers \ {p}; end do; end while
Note that unlike your version, this loop iterates through peers in a non-deterministic order, and that this will generate more states when you use TLC for model checking.
Stephan
Hey Stephan, thanks for the clarification and answer.
Sorry for not explaining correctly, but I want to simulate the messages sent for peers. So basically, in the end the variable msgs should look like this msgs = [n_1 |-> {[t |-> "PROPOSE", v |-> "v_1], [t |-> "ECHO", v |-> "v_1]}, n_2 |-> {[t |-> "PROPOSE", v |-> "v_1], [t |-> "ECHO", v |-> "v_1]}, n_2 |-> {[t |-> "PROPOSE", v |-> "v_1], [t |-> "ECHO", v |-> "v_1]}]
And there will be a several processes like SendPropose or SendEcho that would append to set of messages. So sadly your proposed solution will not work :/
I've made loop like this work, but I'm wondering whether it would be possible to make it look more pretty
while index <= Len(SetToSeq(peers)) do peer_id := peers[index]; msgs[peer_id] := msgs[peer_id] \union {[t |-> "PROPOSE", v |-> input]}; index := index + 1; end while;
Deividas On Wednesday, December 21, 2022 at 9:38:07 AM UTC+2 Stephan Merz wrote:
In PlusCal, "with x \in S do ..." expresses non-deterministic choice, not a loop. The body of the "with" instruction is executed for some peer, then TLC backtracks and explores the remaining choices. Remember that TLC is a model checker that explores all runs of an algorithm, not an interpreter that generates one run. Therefore, "print" instructions are often hard to interpret.
I am not sure what exactly you are trying to achieve. The end result can of course be obtained by writing
msgs := [pid \in peers |-> [t |-> "PROPOSE"]]
Stephan 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.
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 :"
\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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