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*From*: "'Ashish Negi' via tlaplus" <tlaplus@xxxxxxxxxxxxxxxx>*Date*: Thu, 26 Oct 2023 09:24:29 -0700 (PDT)*References*: <c9b89fe7-8c0d-41dd-9d7a-d33b7b2287d8n@googlegroups.com> <B12DF474-2921-44E2-99F6-F6169D0461E5@gmail.com>

Thank you Stephan. This makes sense.

On Thursday, October 26, 2023 at 2:12:33 AM UTC-5 Stephan Merz wrote:

Hello,writing a formal specification in a language such as TLA+ is different from writing a program. In particular, efficiency is (in principle) not a concern. From what I understand, you want to maintain a set of records such that when inserting a record, you overwrite any existing record with the same key. One way to define such an insert operation is(* Insert record rcd in set S but overwrite any existing record in S with the same key *)InsertWithUpdate(S, rcd) ==(S \ {r \in S : r.key = rcd.key}) \union {rcd}A similar operation can be defined on sequences, but it is a little more cumbersome and will have to be recursive.The easiest way to denote the function with the empty domain in TLA+ is to write << >>. Remember that sequences are functions, too.Hope this helps,StephanOn 25 Oct 2023, at 01:06, thisismy...@xxxxxxxxx <thisismy...@xxxxxxxxx> wrote:HiIn last few specs that i wrote, i naturally start with using set of records for variables like set of files. Then i hit the problem that i need to deduplicate these sets based on key field of record.e.g. for set: {[fileId: Nat, cleanupTime: Nat]}, when i insert {fileId:1, cleanupTime: 2} and {fileId:1, cleanupTime: 3}, i don't want to have 2 items in set but only one. I want set to look at `field` fileId as key for set.Is this possible ? From my search, i could not find this.Then i move to using sequences and writing AppendIfNotPresent(s, x) functions myself.I realized that since sequence is a function, can i create a function [fileId |-> record] ? and then updating same fileID can't insert 2 records.I believe someone already thought about this. What are cons of this approach ?About using function, I got stuck at initializing variables with an empty function in pluscal. How do I create an empty function ?ThanksAshish--

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**Follow-Ups**:**Re: [tlaplus] Set vs Functions for modelling***From:*ALFREDO RUIZ

**References**:**[tlaplus] Set vs Functions for modelling***From:*thisismy...@xxxxxxxxx

**Re: [tlaplus] Set vs Functions for modelling***From:*Stephan Merz

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