> > "Perhaps more importantly, what improvement do you propose?"
Apologies for top-posting, but what immediately comes to my mind upon encountering the creation of a self-referential (circular/infinite) object is proverbially 'going-down-a-level' and trying again. So I tried 1. 'decontainerizing' the object on the LHS, and then 2. using the ",=" postfix to add an additional element (or many). Nothing worked. Decont: https://docs.raku.org/language/glossary#index-entry-decont Zen slicing as a possible way of 'de-containerizing' : https://docs.raku.org/language/subscripts#index-entry-Zen_slices Even if the ",=" postfix operator were to gain this ability on non-hash objects, then hash-objects would be special-cased in **not** requiring a Zen-sliced decontainerized object on the LHS, so people would have to consider that outcome. Best Regards, Bill. On Sat, Nov 28, 2020 at 8:33 AM Ralph Mellor <ralphdjmel...@gmail.com> wrote: > > > > @r = @r , 'd'; > > > > Okay, that makes sense. So the circular reference I thought I > > was seeing is really there, and it's working as designed. > > > > There isn't anything very useful in this behavior though, is there? > > Yes. > > Here are some relevant results from a search for "self referential" in > the #perl6 and #raku logs. > > 2006 https://colabti.org/irclogger/irclogger_log/perl6?date=2006-01-06#l567 > > stevan: dunno about ML (or whatever TaPL uses), but IIRC scheme's > letrec is a form of let which allows things to be self referential > > 2012 https://colabti.org/irclogger/irclogger_log/perl6?date=2012-01-01#l107 > my $ff=1; > constant @primes = > 2, 3, 5, > -> $n is copy { repeat { $n += 2 + ($ff=!$ff)*2 } until $n %% none > @primes ... * > sqrt $n; $n; } > ... *; > say @primes[^10]; # OUTPUT«2 3 5 7 11 13 17 19 23 29» > > 2012 https://colabti.org/irclogger/irclogger_log/perl6?date=2012-10-05#l582 > > TimToady: I'd like to get to the point where we can do hamming numbers > self referentially > constant @hamming = 1, dedup (@hamming X* 2) M (@hamming X* 3) M > (@hamming X* 5); > > 2014 https://colabti.org/irclogger/irclogger_log/perl6?date=2014-11-02#l823 > > lizmat: my main reason for not pursuing self referential structures in .raku > > lizmat: was that I didn't have a solution for representing them > > lizmat: thoughts on that are very welcome > .... > > moritz: lizmat: I fear it must be printed out exactly like that > > 2015 https://colabti.org/irclogger/irclogger_log/perl6?date=2015-08-17#l1558 > > vendethiel: TimToady: I read the backlog a bit, but I'm not sure I read the > answer to this question: do you want "my @a = 1, @a" to be (1, 1, 1 > ...) (à la haskell)? > > TimToady: not sure it makes sense with 'my' due to assignment semantic, > but would certainly be nice if 'constant' could be self referential > > TimToady: and we might intuit a lazy if we see the same symbol on the left > > and right > > TimToady: haskell obviously never needs to have explicit lazy, since > > everything already is... > . > > Also (the immediate point, really) this isn't described very well > > in the documentation. > > I'd say the first focus is best `.raku`. But perhaps it's already optimal. > Then again, I imagine "thoughts on that are very welcome" still applies. > > It's always appropriate to consider improving the doc, especially > imo if a draft of an improvement is written by, or in cooperation > with, folk who encountered a problem.. > > > Just to be thoroughly clear, since with a hash this works ... > > My first guess was that for arrays, this would work: > > But here, while @all_at_once is just: [a b c] the array > > @in_stages has a peculiar structure containing circular references. > > Each hash in a list of hashes is automatically flattened: > > my %hash = { :a, :b }, { :c, :d } > say %hash; # {a => True, b => True, c => True, d => True} > > Whereas each array in a list of arrays is not: > > my @array = [ :a, :b ], [ :c, :d ]; > say @array; # [[a => True b => True] [c => True d => True]] > > This is the "class dependent" aspect of the semantics of `=`. > > You could create a new array type SteamRolled and bind that: > > my @array is SteamRolled = [ :a, :b ], [ :c, :d ]; > say @array; # [a => True b => True, c => True d => True] > > Then using the `,=` op would do as you desire. > > > say @r; # ( [<CIRCULAR REFERENCE> d]) > > "Thoughts are welcome". :) > > > And not to quibble too much, but if you didn't want this to do > > that to the array, then it *is* "mangling" it. > > I hear you don't feel sufficiently heard about it being "mangling", > but I just wanted to be clear it was not doing what you may have > thought was going on, namely exhibiting an unintended bug. > > > I think that means you're never going to want to do this. > > It could be it should even be warning or erroring out. > > Per the above IRC discussions, self referential data is useful. > > That said, Larry's comment above about perhaps outlawing it > for `my` variables and instead only allowing it for `constant`s is > the way to go. > > > > It isn't really anything to do with "class dependent" behaviour. > > > > In which case, the documentation could use some improvement. > > I am always supportive of at least discussing improvement of any > aspect of Raku, especially in response to someone experiencing > a surprise or confusion. > > My comment above was meant to be about `,=`. > > The difference in behaviour between arrays and hashes for what > they do when a list is assigned *is* class dependent behaviour. > > > (Actually, saying that some behavior in Raku is class dependent is > > kind of redundant... it's all class dependent in one way or another.) > > Right. But I think *something* needs to be said about how the LHS > gets to decide what happens when you use `=` based on the class > of the LHS.. > > This is different from what happens with, say, `:=`, where the overall > behaviour is essentially the same regardless of the class of the LHS. > > > > Perhaps more importantly, what improvement do you propose? > > > > Well, I just mentioned a few. I always want to see more examples > > in the docs. > > Write them, collaborating with those working on the doc to improve > it, and I predict your wishes will come true. :) > > > What else would you use ,= with besides a hash? > > Any data structure / composite class. > > > It could be my confusion here is another form of something else > > that keeps tripping me up. Merging two hashes together is > > pretty simple: > > > > my %h_all = %h1, %h2; > > > > But doing the same thing with arrays is going to require slipping > > the values out of the containers: > > > > my @a_all = | @a1, | @a2; > > > > So the two cases aren't all that parallel. > > Exactly. > > Hashes autoflatten by default, because that's the only sensible thing to do. > > Arrays do not, because doing flattening by default makes it awkward to > build data structures. > > ---- > > To be clear, imo someone's sense that something isn't right is > always entirely valid. and usually a useful thing to bring to the > table to improve both their own understanding and Raku. > > What wasn't so clear to me was how best to discuss it, so I've > ended up writing very dry stuff. I hope that I haven;t sounded > dismissive, because I am absolutely not intending to do aught > but encourage you to stay with what you are journeying thru > in regard to the impact of trying `,=` with an array, and having > in mind its use with a hash, and figuring out how to improve > Raku semantics, gists, doc, or whatever else is appropriate, > > Much love to all, raiph
