On 12 Nov 2020, at 04:26, Ashish Negi wrote:Q. does [i \in 1 .. Len(files) |-> files[i].id] gives back a sequence ?Yes: in TLA+ a sequence is a function with domain 1..n, for some n \in Nat.Q. Is there something like a REPL where i can try different statements of TLA+ to check the output ?You can use TLC to evaluate constant expressions.Is sequence a set or primitive type ?Semantically, all TLA+ values are sets, but there are many values for which it is not specified which sets represent them. These include numbers and functions, and therefore also sequences and records. It is more useful to think of these classes of values as being primitive.StephanOn Tuesday, 10 November 2020 23:17:42 UTC-8, Stephan Merz wrote:As far as I can tell, your attempt failed because a sequence is a function whereas the construct [x \in S |-> ...] expects a set S. Why not simply[i \in 1 .. Len(files) |-> files[i].id]where files' is your input sequence?StephanOn 11 Nov 2020, at 06:03, Ashish Negi wrote:HiI have a sequence of records with field id`. I want to get a sequence of all ids from original sequence.My first attempt was to try this :[r \in some_sequence_of_records |-> r.id]"The exception was a java.lang.RuntimeException: util.Assert\$TLCRuntimeException: The domains of formal parameters must be enumerable.The error occurred when TLC was evaluating the nestedexpressions at the following positions:    The error call stack is empty."Q1. Is "some_sequence_of_records" a set with DOMAIN 1..Len(sequence) ? Q2. What is wrong with my first try ?Currently, i am using custom map and filter functions for the sequences.RECURSIVE mapSeq(_,_,_)mapSeq(seqs, M(_), result) ==    IF seqs = <<>>    THEN result    ELSE mapSeq(Tail(seqs),                    M,                    Append(result, M(Head(seqs))))GetAllIds(files) ==    LET getId(r) == r.id    IN mapSeq(files, getId, <<>>)Q3. Is there a better way ?ThanksAshish -- You received this message because you are subscribed to the Google Groups "tlaplus" group. To unsubscribe from this group and stop receiving emails from it, send an email to tla...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/tlaplus/5f09aa29-391f-49f1-833f-c6200fa2450co%40googlegroups.com. -- You received this message because you are subscribed to the Google Groups "tlaplus" group. To unsubscribe from this group and stop receiving emails from it, send an email to tlaplus+unsubscribe@xxxxxxxxxxxxxxxx. To view this discussion on the web visit https://groups.google.com/d/msgid/tlaplus/a956a38f-2ecf-4066-b0a7-167a69d400cco%40googlegroups.com. -- You received this message because you are subscribed to the Google Groups "tlaplus" group. To unsubscribe from this group and stop receiving emails from it, send an email to tlaplus+unsubscribe@xxxxxxxxxxxxxxxx. To view this discussion on the web visit https://groups.google.com/d/msgid/tlaplus/FE4429D3-9599-4769-A361-7E9142307502%40gmail.com.