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# Re: [tlaplus] IS there any way of applying \A and \E on sequences in PlusCa l? <EOM>

Here are a couple fo examples:

ToSet(seq) ==

{ seq[i] : i \in DOMAIN seq }

BlockHasMessages(block,channel) ==

IF Len(channel) >0 THEN

\E message \in ToSet(channel) : block.id = message

ELSE

FALSE

In this example, if  I remove the ToSet(channel), it gives an error. channel is a sequence. So \E in TLA+ seems to work on sets but not on sequences.

Second one

TypeOK ==

\A block \in Blocks:  block.state \in StateSet

where Blocks is a structure , which is a sequence as per documentation

Blocks =  [

a |->  [ id |-> "a", state |-> "waiting", inputs |->0, outputs|-> <<"b","c">>],

b |->   [ id |-> "b", state |-> "waiting", inputs |->1, outputs|-> <<"c","d">>],

c |->  [ id |-> "c", state |-> "waiting", inputs |->2, outputs|-> <<"d">>],

d |->   [ id |-> "d", state |-> "waiting", inputs |->2, outputs|-> <<>>]

];

This results in a  usinga quantifier of a non-enumerable error.

On Sunday, 14 August 2022 at 18:06:07 UTC+5:30 Stephan Merz wrote:
Hello,

PlusCal expressions are the same as those in TLA+, and if your question is if the formulas in the definitions below:

Reverse(s) == [i \in 1 .. Len(s) |-> s[Len(s)-i+1]
IsMirrorSeq(seq) == \E s \in Seq(Nat) : seq = s \o Reverse(s)

are well-formed TLA+ formulas, the answer is yes.

Tools for TLA+ impose different restrictions on what kind of formulas they can handle. For example, TLC will not be able to evaluate the formula IsMirrorSeq(<<0,1,1,0>>) out of the box, but you can override the Seq operator to impose a bound on the length of sequences. More information on how to do this is available in the Help pages.

Hope this helps,
Stephan

On 14 Aug 2022, at 06:15, Anand Kumar <akkes...@xxxxxxxxx> wrote:

I am new to this, and would appreciate any pointers in this matter.

Thanks in advance

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