From @zoffixznet

While adding a test[^1] it was discovered that `[]` metaops containerize their product sometimes​:

Inconsistent containerization​:
  <Zoffix> m​: say ([\,] <a b>, <c d>).perl
  <camelia> rakudo-moar 79f268​: OUTPUT​: «(($("a", "b"),), ($("a", "b"), $("c", "d"))).Seq␤»
  <Zoffix> m​: say ([,] <a b>, <c d>).perl
  <camelia> rakudo-moar 79f268​: OUTPUT​: «(("a", "b"), ("c", "d"))␤»

Inconsistent return type​:
  <Zoffix> m​: say WHAT ([,] <a b>, <c d>)
  <camelia> rakudo-moar 79f268​: OUTPUT​: «(List)␤»
  <Zoffix> m​: say WHAT ([\,] <a b>, <c d>)
  <camelia> rakudo-moar 79f268​: OUTPUT​: «(Seq)␤»

Lastly, by reading the code alone, there looks to be another inconsistency where some triangle reduction
metas .push[^3], while others .append[^4] their values. There was one change[^5] from .append to .push that
fixed a problem[^6], but looks like other meta op configurations still have it.

IMO it's important to have consistency in all three of these aspects in order for users to be able to easily
predict what sort of return values they would obtain.

[1] https://github.com/perl6/roast/blob/ecf59598811cbe6a8c751f3ae342868f10de126c/S13-overloading/metaoperators.t#L50-L60
[2] Raku/roast@c30eb54#commitcomment-21359198
[3] https://github.com/rakudo/rakudo/blob/79f2681004224108b2acd18bec21b76803eb8fcd/src/core/metaops.pm#L407
[4] https://github.com/rakudo/rakudo/blob/79f2681004224108b2acd18bec21b76803eb8fcd/src/core/metaops.pm#L427
[5] rakudo/rakudo@d56501a
[6] https://rt-archive.perl.org/perl6/Ticket/Display.html?id=130610

From @zoffixznet

The comments on return type are bogus, since non-triangle meta op can return whatever type the op produces...

From @FCO

Em Sat, 18 Mar 2017 13​:38​:24 -0700, cpan@​zoffix.com escreveu​:

The comments on return type are bogus, since non-triangle meta op can
return whatever type the op produces...

The fiz can be found at rakudo/rakudo#1046
And the tests at Raku/roast#258

The RT System itself - Status changed from 'new' to 'open'

@FCO - Status changed from 'open' to 'resolved'