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Set by sjohnson on 22 January 2010.
sjohnson diakopter: what OS do you use for your desktop day to day use? 00:00
00:03 patspam joined
pugs_svn r29580 | lwall++ | [S03,S07] more Pm-16 refinements 00:05
s1n_mini sjohnson: i proudly use Windows 95, as God and Gates intended :) 00:08
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sjohnson serious?! 00:08
s1n_mini unpatched as released in 1996 :) 00:09
no i'm just kidding lol
sorry for the off-topic, this class is seriously boring 00:10
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TimToady sjohnson: wasn't foresight, just experience that once spam attacks start, they usually continue :/ 00:11
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TimToady and also laziness in not figuring out any other options :) 00:11
sjohnson TimToady: one of the bots called me a fat face! please do something about this
TimToady did I mention it will be impossible to do evil programming in Perl 6? :) 00:12
sjohnson s1n_mini: i like off-topic if im not interrupting anyone's heavy perl log.. reminds us that we all aren't robots
s1n_mini TimToady: care to test that?
TimToady test what, whether I mentioned it? 00:13
s1n_mini it's truthiness
sometimes, evil things can be fun, if only to prove a point :) 00:14
TimToady it was kinda sad, the day PHP took over from Perl as the language of choice for network abuse...
sjohnson and lazy scoping abuse too
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sjohnson now these PHP users have grown up, and are in our officez, programmin' our softwares 00:15
Juerd PHP's scoping is so annoying.
s1n_mini can haz pee h pee
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Juerd The workaround is to write millions of tiny functions 00:16
sjohnson Juerd: have you read the common PHP vs Perl milestone in html web publishing?
Juerd No, what's that? 00:17
sjohnson tnx.nl/php.html
Juerd Seriously?
I kind of wrote that :)
sjohnson thats yours? 00:18
Juerd Yea
sjohnson wow
small world!
that's amazing
i've pasted that link to tons of people 00:19
whenever they ask "... but i like PHP"
Juerd Thanks
It's so damn incomplete though :(
sjohnson well, if you ever thought of ammending it 00:20
you'd have my full support!
Juerd I have. On average once per week I think.
But I lack real motivation and inspiration.
It's hard to make a point without much text 00:21
s1n_mini Juerd: that image does a good job
Juerd merlyn posted that line to perlmonks 00:22
sjohnson Juerd: did you see my addition on the graph of programming languages, what Perl programmers think of PHP?
Juerd He let me use it for the poster :)
sjohnson: No 00:23
sjohnson Juerd: imgur.com/LPPaL.jpg
i only added in the X and Y's of the Perl part
took me quite a while
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sjohnson but i think youll like the what Perl thinks of PHP 00:23
Juerd Hah 00:24
I like Mickey Mouse better than PHP though :)
sjohnson same
my brother and i always say "PHP.. such a Mickey Mouse language"
i had to stick it in there
s1n_mini maybe blue's clues is more appropos 00:25
sjohnson heh
i only learned about Deep Blue a while ago
if that's what you mean
starting to learn how to play chess
TimToady more like teletubbies, I think 00:26
LaVolta morning, everybody!
s1n_mini no, the blue dog for kids
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Juerd Do you know about the lego/playmobil comparison? 00:26
juerd.nl/site.plp/perl_lego
diakopter everyone needs a Pretty Home Page 00:29
Juerd It's weird how Personal Home Page became PHP: Hypertext Preprocessor
But as a simple preprocessor in the cpp sense, I don't mind PHP :)
It's much faster than Template Toolkit :( 00:30
diakopter o
Tene PHP was a great, simple, limited language for adding small amounts of dynamic behavior to an otherwise-static site. It's a shame nobody developed it after the first couple of years. 00:31
Juerd It has never been great and simple, IMO.
s1n_mini one man's trash is another man's treasure
sjohnson PHP is good to teach complete newbies how to program 00:32
basics of for loops, etc
Juerd sjohnson: Oh no.
Tene Eh, I was just guessing. I never saw the early versions, so I just assumed they were sane at one point.
sjohnson because it is very tolerant
Juerd sjohnson: It's all but tolerant. How can you say it's tolerant?
s1n_mini wasn't based on perl4?
sjohnson Juerd: because newbs who are new and have thin skin.. wont cry when they see a scoping error in PHP
Juerd: and they dont have to memorize sigils, etc.. i just mean as an absolute beginners language
and then once you know what a for loop is, dump PHP 00:33
or learn Perl but dont use scrict;
perl == better
s1n_mini class over, later
sjohnson cya
Juerd sjohnson: I've taught Perl and PHP to absolute beginners. Obviously I'm better at teaching Perl because I'm more familiar with it, but it's much easier to let kids play with Perl than with PHP.
diakopter function ($y) use ($x) {
sjohnson Juerd: ill take your word for it. i found learning Perl with the camel book DEAD simple 00:34
and intuitive
Juerd Perl will give meaningful error messages on syntax errors, whereas PHP's are incomprehensible and often misleading.
sjohnson i had perl learned in less than a week flipping through the camel book at work for a few hours a day
Juerd: i dont like those really arrogant PHP kidz you see around.. on slashdot or irl
who think they are scripting gurus cause they know a bit of PHP 00:35
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sjohnson mirc scripts to annoy ppl are the same ilk of ppl 00:35
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Juerd sjohnson: Oh, and I do teach them to use strict. Newbies make lots and lots of typos in identifiers, at least those that I've instructed. 00:35
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Juerd But my only audience has been kids, ages 14..17 00:36
Tene same in my perl classes for adults
sjohnson TimToady: hopefully not a silly question.. but have you ever played around / used PHP much? 00:38
i have to use it at work, otherwise i probably wouldn't use it
LaVolta just wondering why nobody metions Python for beginners...
diakopter
.oO( more than half of folks in here aren't identified and aren't voiced
 00:39
)
TimToady sjohnson: nope, not something I've ever aspired to
sjohnson diakopter: most of them don't even chat in the chan either
and if they try to... freenode will just alert them, to please register 00:40
and so will the topic... they should be ok methinks
just think of the happiness of not having bots!
diakopter it didn't alert me when I tried to talk in the channel
pmichaud okay, while out fetching dinner I think I realized that my thoughts on list and iterators are, in fact, completely bogus :-|
sjohnson are you sure you didnt get a CTCP diakopter ?
"Users will receive a server notice explaining this if they try to speak. " 00:41
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diakopter sjohnson: ok 00:41
pmichaud: 'completely'?
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pmichaud diakopter: if not 'completely', then perhaps 'seriously misguided'. 00:43
sjohnson diakopter: i got a server message testing it out asking me to register
just to confirm i tested it
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Tene pmichaud: explain? 00:43
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pmichaud let's consider a statement like 00:44
@a = (4, 5, 1..1000, 7);
rhs is a List 00:45
TimToady or a Parcel
pmichaud (well, it's a Parcel that ends up acting like a List because it's in list context)
the current ng implementation has been saying that yes, Lists are (externally) immutable
so the List starts out with four things in it, the 4, the 5, the range, and the 7 00:46
as we start to iterate over the list, though, it takes the lazy range and starts making it into elements in the "generated" part of the list
thus as we're doing the assignment, at some point the rhs ends up looking something like (4, 5, 1, 2, 3, 4..1000, 7)
Tene Ouch. 00:47
pmichaud i.e., we're taking elements off of the iterated range and putting them into the generated portion of the list
colomon nods
sjohnson Juerd: if i can think of a bad thing to add to your site, i will add it. i have to use PHP at work fulltime so i have come across a lot of crap
pmichaud but we really don't want those elements there -- they're not going to be needed
in other words, when we're iterating any sort of list, the more common case is that we really want to be throwing elements away, not preserving them
colomon I was wondering about that. I keep thinking of the for 1..10000000 case.... 00:48
TimToady well, if you work ahead some, you have to track the generated but not yet consumed values
so I don't think the view is entirely inaccurate 00:49
pmichaud it may not be entirely inaccurate, yes
but the implementation is working too hard to preserve the immutable nature of Lists
when a List's immutability is really not all that important in most cases 00:50
(immutable in an external sense, not an internal one)
TimToady to the first approximation, lists are not generally user-accessed
pmichaud right
TimToady as in Perl 5, they're internal thingies
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pmichaud well, in Perl 6 they still tend to show up a bit 00:50
for example: my $a = (1,2,3); say $a.WHAT; 00:51
that's likely to be a List.
TimToady I'd argue Parcel, I think.
maybe, still waffling :)
pmichaud if that's the case, then rakudo-ng's model is even more broken.
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sjohnson i have had a few instances where i wnat to keep the lists data. i was hoping to not have to write the $_ in $_ is copy 00:52
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pmichaud in general, rakudo-ng says that any Parcel in item context becomes a List. 00:52
more to the point, we'd somewhat expect my $a = (1,2,(3,4), 5); say $a.elems; # 5 00:53
where .elems is a method on List
TimToady is trying to figure out one can assign an item a Parcel value...
pmichaud right -- in Perl 6, it feels like Parcels end up being the "invisible internal thingy" 00:54
and List is more visible
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TimToady btw, I think whatever else we decide @$x and @($x) have to do the same thing 00:55
pmichaud (caveat all statements here with my overall observation that suddenly something feels fundamentally wrong about rakudo-ng's List implementation to me)
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pmichaud oh, *that's* interesting also :-) 00:55
that's the way I had been thinking of it, but I noticed yesterday the spec doesn't say that
and it becomes a little weird in the case of @$x, 3 versus @( $x, 3 ) 00:56
TimToady I think that case is handled by the autoreduction of item Parcels
pmichaud I'm confused there, then. 00:57
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pmichaud (not surprising. I just realized as I was walking into "Tasty Egg Roll" that my mental model is now a mass of confusion :-) 00:57
TimToady if $x contains, say [1,2,3], @$x derefs, but @($x, 3) doesn't, since the $x is embedded in a Parcel with 2 elements 00:58
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TimToady but @($x) is a Parcel with one element, and therefore [1,2,3] derefs 00:58
pmichaud right
that's fine w/me (and fits with how I thought of things before yesterday)
so, @($x, 3).elems == 2
TimToady yes
pmichaud wfm 00:59
LaVolta TimToady, you mean in @($x) case it will become @$x ?
pmichaud while (@$x, 3).elems == $x.elems + 1
TimToady LaVolta: that would be another way to say it, but yes
say rather that @$x is shorthand for @($x) 01:00
pmichaud LaVolta: essentially, in the @($x) case it's operating on $x. In the @($x, 3) case it's operating on the parcel ($x, 3)
LaVolta ah...thanks, got it :) 01:01
pmichaud oh! 01:02
TimToady pmichaud: I could almost argue that $x = is contextless, while $x := is item context
pmichaud upon thinking about it further, perhaps Rakudo has it right after all!
let's re-examine the @a = (4, 5, 1..1000, 7) case again 01:03
TimToady but no, then $x = (1,2,3) would interpolate $x into a list, which is a bit of a nono
pmichaud what Rakudo-ng is doing now (rightly or wrongly) is turning the rhs into an Array
and then it is shifting elements from that Array
which means the intermediate elements aren't being stored 01:04
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pmichaud the original List still exists -- what Rakudo-ng does now is to create an Array from that List and use it for the assignment 01:04
TimToady alternately, just take the list, poke it into the Array's generator spec, and then tell it to reify mostly eagerly 01:05
why copy twice?
pmichaud long story
but mainly to be able to deal with something like ($b, @c) = ( 1..$something, $b )
TimToady I think assignment is to a new $b and a new @c, and those are rebound to the variables upon completion, maybe 01:06
pmichaud yeah, that doesn't fit Parrot's model all that well. And we have to deal with other bindings for $b and $c 01:07
i.e.
$a := $b; ($b, @c) = ( 1..$something, $b );
at the end, $a still needs to be bound to (new) $b
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TimToady well, somehow we have to take a transactional view, and commit the change after creating the new values for $b and @c 01:08
but after using the old values eagerly
pmichaud right. At the moment rakudo accomplishes that by creating an Array and copying from that (the Array can still be lazy) 01:09
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pmichaud I have some tricks to avoid the dual copies 01:09
anyway, here's a more interesting case
for 4,5,1..1000,7 { ... }
this is another case where we want to be able to iterate over the array and throw away the generated values 01:10
s/array/list/
TimToady sure, I guess I don't see a problem
pmichaud well, the way rakudo-ng is currently handling List, it keeps track of generated values
because the List is "immutable" 01:11
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TimToady it's only immutable in the abstract 01:11
pmichaud right
but internally, how to represent that?
TimToady you can throw away values that can't be gotten back to 01:12
pmichaud how do we know "can't be gotten back to"?
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TimToady iterated externally, since a List is, to the first approximation, an iterator of iterators 01:13
pmichaud ...and that's where Rakudo gets it wrong, then.
TimToady we might want to do like with Range and distinguish List from ListIterator 01:14
pmichaud rakudo-ng already does that
TimToady the only time you need the whole list is in situations like (4,5,1..100,42)[@ix]
where @x can visit the elements in any order 01:15
in that case, it presumably promotes to Array
pmichaud hopefully not
my $x = (1,2,3); say $x.WHAT; say $x[1]; say $x.WHAT; # auto-promotes? 01:16
TimToady I don't think List can be Positional, or you always have to remember it all
that's bogus
pmichaud is Parcel Positional? 01:17
TimToady yes, but on syntactic elements
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pmichaud if we don't have to remember all of the parts of a List, how is it immutable? 01:17
TimToady (1,2,1..1000,42) has 4 elements
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pmichaud "has 4 elements" in the sense that calling .elems on it would give me back 4? 01:18
TimToady just in the sense that a given list, once you've determined the value of the nth element, will never determine a different value for it
that doesn't mean it's accessible
0..* is 0,1,2,3,4,5, and the values are always those values 01:19
but 'for 0..* {...}' doesn't have to store all the values
pmichaud but how do we know that?
TimToady because we iterate the list, and iterating is forgetting 01:20
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TimToady all iterators are mutable in that sense 01:20
pmichaud so if a List is really a iterator of iterators, it's mutable in that sense also? 01:21
TimToady yes
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pmichaud what about something like 01:22
(1..3).map( { $_ * 2 } ).[5,3,7]
is .map returning an Array there?
does it return something that auto-promotes to an Array?
(can't be a List if lists aren't positional) 01:23
TimToady the subscript must autopromote it to something Positional
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pmichaud so, subscripting a List promotes the List to an Array? 01:23
TimToady could do like Perl 5 and index the stack directly though
or whatever is functioning as the temporary value 01:24
could perhaps even be handled by Cool.[]
pmichaud perhaps subscripting just turns on a flag that tells the List "you have to remember values now" ?
TimToady well, that would be an optimization 01:25
pretend to be an Array for a moment
pmichaud well, I kinda need to know if it auto-promotes
in the sense that a programmer sees the actual promotion
TimToady $list.[] doesn't have to mutate the type of $list 01:26
pmichaud okay 01:27
TimToady it might, however, consume as much of the list as it likes to get to the biggest index
pmichaud well, if I had $list.[5] and later $list.[4,5] I'd probably like the 5 element to be the same one 01:28
so it generates (and stores) as much of the list as it likes to get to the biggest index it's seen thus far
TimToady well, that argues that $x = (1,2,3) promotes to Array immediately
like we used to :) 01:29
which is probably okay, given that Arrays can auto-extend lazily
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pmichaud I was thinking the same thing, but why does it need to promote to Array immediately? 01:29
why can't $x remain a List ? 01:30
TimToady because Array's are for remembering positions
pmichaud can a List just be an iterator that remembers positions if you need it to?
I can see why that wouldn't work, though.
TimToady translation, can a List just behave like an Array?
pmichaud well, an "immutable" Array 01:31
TimToady we've already built the autogen into Array semantics, so it seems redundant to also try to make List work both ways
pmichaud agreed, there redundancy here that I've been unable to resolve.
*there's
TimToady I think lists are not positional 01:32
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pmichaud rakudo-ng has the autogen in List semantics, and then uses that to derive ARray 01:32
TimToady and then we wonder when we can GC the used values of the list 01:33
pmichaud (I agree that feels wrong now)
part of the reason rakudo-ng does it that way, though, is because Array ~~ List
TimToady not sure List is a useful type 01:34
pmichaud (perhaps that shouldn't be the case)
oh, I'd be just fine with eliminating List altogether if it's not in fact useful
I never have quite grokked the difference between List/Array and Mapping/Hash
other than mutability
TimToady Array ~~ IterableByClonedIterator 01:35
pmichaud cloned iterator? In the sense that it actually clones the Array?
TimToady in the sense that the Iterator is not an Array
any you might have several pointing to the same Array
*and 01:36
pmichaud and modifying the array leaves the iterators in an undefined state?
(doctor, it hurts when I do that...?)
TimToady presumably, depending on how fancy we get
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pmichaud if we eliminate List, then that leads towards the notion I had last year that Parcel and List actually did similar things. 01:37
i.e., we're just left with Parcel
TimToady a Parcel is a list of iterators
pmichaud I tend to think of it as a list of syntactic elements
and what happens to it depends on the context in which it's used 01:38
so, subscripting a Parcel would turn it into an Array
TimToady yes, but that's dynamically determined in the general case
though we can recognize where to transmute to Capture most of the time
pmichaud correct
iirc, p5 makes a fair bit of noise about the difference between "list" and "array". Does eliminating List from p6 cause us an issue of any sort? 01:40
TimToady $x = \(1, 2, 1..1000, 42); say $x.[2].WHAT # Range
well, list context is what iterates iterators in Perl, generally 01:41
but in Perl 5 the iterators can't be stored into $x
I think we should probably make it difficult in Perl 6 as well, though possible
since for $iterator {...} isn't going to do what people expect, one way or another 01:42
pmichaud well, I did observe earlier (in backscroll to colomon) that except for filehandles, p6 iterators tend to be invisible also
generally it'd want to be for @$iterator { ... }
or something like that 01:43
eliminating List would also clean up another bit of ickiness in rakudo-ng (more) 01:44
diakopter sjohnson: my point was that everyone who's currently a member of #perl6 should be voiced
pmichaud right now invoking a method on a Parcel causes it to autopromote to a List
if we eliminate List, then we can leave it as a Parcel 01:45
diakopter sjohnson: b/c they're not going to know they need to register/identify to be heard
sjohnson: oh wait, nm. <sigh> /me shuts up
pmichaud or have it autopromote to an Array
sjohnson ( ╹◡╹)
LaVolta diakopter, add that to MOTD? :-P
diakopter still, not everyone watches their CTCPs (or even know what to watch, or why or what they'd be watching) 01:46
sjohnson let us pray they read the topic 01:47
pmichaud TimToady: okay, thanks, I think this helps a fair bit. I'll play with my mental model a bit more and see if I can make some sense out of it (similar to what happened with Nil and Parcel :-)
sjohnson if freenode allowed coloured topics, i would have made it stick out like a sore thumb
kloeri_: what do you think of coloured topics?
kloeri_ I usually try to avoid all the colour stuff as it mostly annoys me 01:48
pmichaud reviews the r29580 commit 01:49
kloeri_ most networks doesn't support ansi codes in topics afaik since /list could get rather interesting if they did
sjohnson 4friend!
kloeri_ heh 01:50
sjohnson kloeri_: is the spam bot harassing other freenode channels?
kloeri_ tons of channels, yeah
sjohnson any hope of resolution? or new ircd is the answer
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sjohnson so far this +R technology seems to do the trick well 01:51
kloeri_ new ircd is the real answer
sjohnson though may cause annoyance to others as dia mentioned
kloeri_: is there an EST date?
kloeri_ until then +R will do, hopefully without causing too much annoyance
jan 30th is the migration 01:52
sjohnson fantastic then
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sjohnson well gtg thanks for your help kloeri_ 01:53
kloeri_ you're welcome
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pmichaud Tene, colomon, jnthn: see backscroll above for thoughts on lists and iterators, let me know if you have ideas or comments 02:01
afk, late dinner
colomon roger
Tene pmichaud: I've been reading. :)
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colomon pmichaud: what keeps on jumping out at me is that there are iterators everywhere. 02:11
That is, you want to iterator over the list, and you want iterators to generate the list.
TimToady pmichaud: I think we promote an item Iterator to Seq, and define Seq to be extensible like Array, but readonly in the reified bits 02:13
also thinking that Iterate is the role that does .get, while Iterable means you can create an object that does Iterate
colomon and in the ideal world, if you only want to create the list to get its iterator, you don't want to store the values in it.
TimToady so an Array does Iterable, but not Iterate 02:14
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colomon TimToady: so Array would return an ArrayIterator, or something like that? 02:15
TimToady either that, or iterators are Iterable, and other things are Iterableable
colomon: nodnod
colomon One thing pmichaud and I were talking about is how you know when the Iterator is done. 02:16
the spec says .get returns Nil in that case, but isn't Nil a valid value in a List / Array?
TimToady a list-flattening iterator will throw away an embedded Nil so that the user never sees it 02:18
colomon TimToady: hmmm....
TimToady a slice iterator can return a Nil as an element, so something else will have to signal the end
either that, or a slice iterator promotes Nil to []
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Tene drives home 02:18
colomon we talked about .get returning two values, but that's a list, and things quickly get nonsensical. 02:19
jnthn pmichaud: I'll read the list discussion tomorrow. EBEERANDCOMPLEXSEMANTICSINCOMPATIBLE.
LaVolta go to take a .NET exam, good luck :-P 02:20
colomon pmichaud was talking about having a separate method to query if the list is done, but that means many iterators would need to store values internally, because you can't know if the list is done until you try to get the non-existent last value.
jnthn LaVolta: Good luck...I did one of those a week or two ago. :-)
colomon I really think having .get return a special value is a good approach, but finding a suitable special value is tricky... 02:21
LaVolta jnthn, thanks...
jnthn LaVolta: fwiw, I passed, so apparently it's not impossible. :-)
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TimToady I think Nil can be okay, given list vs slice semantics 02:22
decommuting &
jnthn I don't really like "you must remember to check the return value" in general, but I need to read the full discussion to get the context. 02:23
colomon pmichaud: I keep on coming back to feeling strongly it's important to have a good iterator interface even if its something 99% of the programmers out there will never touch. It looks to me like the sort of thing that power class designers may want to have available. And I think it's important that as much as possible of p6 can be written in p6.
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colomon jnthn: well, you definitely need to check something to know if the iterator ends! 02:24
the issue is whether it's the return value of .get or the return value of some other function.
pmichaud colomon: (back) I agree it's important to have a good iterator interface. afaik none of us have any real clue what that should look like :-) 02:25
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colomon pmichaud: :) 02:25
pmichaud: TimToady seems to think .get returning Nil to indicate it's done is reasonable. 02:27
I'm also wondering HOP might have something useful to say on this subject.
pmichaud I'm okay with that for now, I think.
colomon *whether HOP
pmichaud colomon++ # HOP might indeed be a good idea here 02:28
for the moment I'm having to get my head around the idea of dropping List altogether
or perhaps List and Mapping are just roles in the same sense as Numeric, Stringy, etc. 02:29
jnthn pmichaud: I'm more used to the "we're out of values" being out of band. That said, most lanuages don't have the idea of undefined in the sense that Perl does.
colomon Wouldn't List just be the Iterable TimToady was just talking about then?
pmichaud colomon: perhaps
jnthn pmichaud: I'd kinda seen List as the immutable version of Array, fwiw.
pmichaud jnthn: right, so had I. But I had the revelation today that this isn't really all that desirable 02:30
consider
for $a, $b, 1..1000000, $c { ... }
do we _really_ want to be storing those million elements as we generate them...?
Tene for iterator interface, I'd imagine it's the same as gather/take. Throw an exception containing the element you want, and then actually return when you're done. 02:31
I need ot htink about whether that actually works, though.
colomon pmichaud: or heck, for $file.lines { ... }
pmichaud Tene: exceptions can work, but they can also be a bit heavyweight at times 02:32
jnthn pmichaud: Good point, and if the assumption is that List does Positional, well, that's awkward in that situation, yes.
pmichaud jnthn: well, that's the other thing -- above TimToady was conjecturing that List !~~ Positional
jnthn Hmm.
pmichaud so the "List as immutable form of Array" isn't really right. TimToady conceptualizes it more as an iterator (of iterators) 02:33
and that fits my more recent experiences a bit closer as well.
jnthn I can go with that.
pmichaud I probably won't have a new model to even begin to work from until tomorrow morning 02:34
(new "mental model", that is)
jnthn My feeling with the enum/hash stuff of late was that we were starting to pull away from the "there's a mutable and immutable version of the various data structures" model.
pmichaud right
so the idea that "List" really means "Iterator" makes sense
colomon HOP: "An iterator is an object interface to a list." :)
jnthn I want to call it iterator rather than list in that case. 02:35
pmichaud I.e., a List is an iteration of some sort
jnthn But I can go with eliminating list or some unification there.
We do need to lay down the semantics though.
If a list/iterator is an immutable view of an array, what happens if the array changes? 02:36
Or is it an immutable view?
pmichaud it's not immutable
jnthn And all that lot.
colomon and it's not a view.
jnthn lol
Thanks guys. :-)
pmichaud if you change an array while it's being iterated, you get undefined results
jnthn Ok.
pmichaud (this is not all that uncommon, even in p5)
jnthn We can define the semantics whichever way, so long as they're defined. :-)
(And if it's defined that it's undefined, that's fine too...) 02:37
Juerd I'm wondering - does the word "list" remain as something to describe the syntax for multiple items with commas in between, even if lists as a type are gone?
pmichaud Juerd: I suspect so.
colomon Juerd: that's what I was just thinking.
pmichaud and it remains the name of a context
jnthn Anyway, I'm not attached to the mutable and immutable version of the common data structures view of the world.
pmichaud i.e., we still have "list context", which says that certain things get interpolated into the list/iterable view 02:38
Juerd pmichaud: Context is, eventually, syntactic too
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jnthn Juerd: In fact, it may help in that it avoids the issue of casting to something that can be used as a list vs to List. 02:38
colomon I'm thinking list might be implemented with an Iterator looks suspiciously like a cons node.
(ie, it's a value and another iterator)
pmichaud colomon: very nice observation 02:39
Juerd jnthn: I'd really like that confusion to be gone because I've never been able to keep them apart
jnthn Juerd: Same. It's like the Numeric vs Num one. 02:40
pmichaud Juerd: I'd say something along the lines of "the comma creates a parcel, which is iterable as a list in list context"
Juerd It's hard enough to know the differences between arrays and lists, or parcels. And at least those have very distinct names. list versus List is too tough :) 02:41
pmichaud in most cases, parcels end up acting like lists
jnthn Parcels don't tend to last long before the magically become something else. :-)
pmichaud well, that may no longer be true :-)
jnthn In the case of calls, they don't even survive until runtime.
pmichaud parcels may start to remain as parcels :-) 02:42
jnthn Not for calls, surely?
pmichaud no, not for calls, except in the abstract
jnthn Right, good.
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jnthn I think I used my "you can panic once" but I might have requested a second right to panic if that one was changing again. :-) 02:42
Juerd What creates a parcel, syntactically?
pmichaud Juerd: comma
jnthn commas. 02:43
Heh, pm beat me to it. :-)
Juerd Very intuitive then, I think
It looks like what we've known as a list, it behaves like one, and it has a better name. I think that's a good combination :) 02:44
Oh, and it can do much more. That's good too.
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pmichaud so, something along the lines of "a list is an iterator that knows how to interpolate other structures and iterators" 02:45
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pmichaud so, we can interate a parcel like 1, 2, $a, @b, 1..5 and that iterator is able to (lazily) get iterators from the array and range to use for interpolation 02:46
jnthn OK, it's 3:45am here and I need to sleep. :-)
jnthn will backlog this lot tomorrow
Juerd pmichaud: What's the name "list" good for then?
pmichaud that's what we call the iterator 02:47
it's a "list"
Juerd Does the parcel need a list to be iterable?
pmichaud a list is really an iteration of elements
especially since a parcel in a difference context would return a different iteration 02:48
or a different result
s/difference/different/
in capture context, the parcel 1, 2, $a, @b, 1..5 has five elements
(Int, Int, Scalar, Array, Range)
Juerd 03:34 <@jnthn> I want to call it iterator rather than list in that case. 02:49
pmichaud also, .list remains the general form of asking an object to return itself as an iterable list
Juerd That's what I'm referring to
pmichaud maybe, but I prefer @a.list to @a.iterator 02:50
since what I get back is a list of the elements in @a
Juerd If a list is just something that can be iterated, then there's no practical distinction between list and iterator anymore, is there?
pmichaud (I might get them lazily, but I do get them)
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vamped so will we be able to iterate both the capture and the items? ie parcel[4] is range, or 2nd item of @b 02:50
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pmichaud vamped: parcel[4] would be the 2nd item of @b, because in most cases we default to list context 02:51
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pmichaud to get to it as a parcel, use the capture prefix: \(1, 2, $a, @b, 1..5).[4] 02:51
vamped and hopefully there will be a way to specify that we want all the items in one flast "list" ?
s/flast/flat 02:52
pmichaud vamped: sure, that's already "list"
Juerd Oh. I was thinking that perhaps parcel[4] would be 1..5, and parcel.list[4] would be @b[1]
pmichaud list 1, 2, $a, @b, 1..5 # flattens
in general we tend to do things in Perl in list context much more than capture context
vamped Good! that point has been confusing to me the past couple of days.
pmichaud with a for statement like 02:53
for 1, 2, $a, @b, 1..5 { ... }
we expect the fifth iteration to be the second element of @b
and not the range
same for
my @c = 1, 2, $a, @b, 1..5; # @c[4] is the second element of @b
vamped but what if $a=1,2,3; ? 02:54
pmichaud scalars never interpolate directly
Juerd Isn't it just syntactic sugar for: iterate (1, 2, $a, @b, 1..5).list { ... } ;)
pmichaud to get that behavior, use
1, 2, $a.list, @b, 1..5
or
1, 2, @$a, @b, 1..5
vamped yes, but if we're dealing with @c (and may not know exactly what is inside) we can't do that 02:55
pmichaud vamped: hmm?
vamped if @c=1,2,$a,@b,1..5; I want to do something like for @c {...} and access all the elements, including what's inside $a if $a=1,2,3; 02:56
Juerd tries to imagine what would happen if we had iterator context instead of list context, and fails
pmichaud yeah, I think "list" is really the word we want
Juerd I find list confusing 02:57
pmichaud vamped: right, there's not currently a shortcut that says to auto-interpolate anything that happens to look like an array inside
(not sure there should be, either)
Juerd In Perl 5 you get away with calling two different thing list because they always coincide
Well, almost always
vamped perhaps you're right about that pmichaud. 02:58
pmichaud Juerd: well, "list" really does mean "iterator"; that's primarily because in p6 lists are "lazy"
but I don't normally talk about the iteration of elements in a Range, I tend to think of it in terms of "give me a list of all of the values in the Range"
Juerd pmichaud: But then it means two things. It describes the syntax with commas and it is a kind of thing. 02:59
pmichaud no, the syntax with commas is a parcel
Juerd I don't think people will ever unlearn to call that a list
pmichaud that's okay, I don't see that as a problem
Juerd I do
pmichaud in most default contexts in Perl 6, it *is* acting like a list. 03:00
and when it's not, there's a keyword or something to explicitly call out the other context
afk for a bit -- need a walk 03:03
Juerd Have fun
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Juerd follows jnthn's example 03:04
Good night
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LaVolta jnthn, fyi, i'm back...however, it's just a course exam...the winter vacation's about to begin. 03:21
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pmichaud okay, after my walk, I think I can mentally get my head around the notion that a list is an iterator (more) 03:40
first, discard the existing notion of List as an "immutable array". In fact, start with a blank slate on the idea of "list". 03:41
When we say "list", we're really talking about a sequence or enumeration of elements.
s/elements/items
an "iterator" is also a sequence or enumeration of items, but instead of computing the entire sequence at the time the iterator is defined, an iterator tells us how to get from one item to the next 03:43
in other words, with an iterator, we don't have to produce the entire sequence at once -- we can produce it lazily
now then, in perl 6, our lists tend to be lazy by default 03:44
LaVolta pmichaud, laziness is true virtue :)
pmichaud in other words, we say that unless something indicates to the contrary, we try to produce all of our sequences (i.e., lists) lazily 03:45
so a "lazy list" is really the same as an iterator
this is in contrast with Perl 5, where lists actually tended to be eager by default 03:46
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pmichaud in Perl 5, it was important to distinguish between "list" and "iterator" because one was eager and the other was lazy 03:46
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pmichaud returning to p6, we still want to call things "lists" instead of "iterators" because we're still talking about sequences 03:47
they're just lazy sequences now instead of eager ones
also, we tend to want to talk about the sequence as a whole ("list") rather than the process that was used to produce the sequence ("iterator") 03:48
perigrin perhaps borrow from HOP and s/list/stream/ ?
pmichaud good idea. but we still want to talk about it as a whole, I think.
perigrin yeah, but a list is potentially finite while stream is unknowable because of it's laziness 03:49
:)
pmichaud in other words, I want to be able to say (1..100).list as opposed to (1..100).stream
perigrin yes
pmichaud so "list" seems like the right term.
anyway, an "array" then is a list that has memory 03:50
perigrin nods
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pmichaud in an array, as we enumerate the elements of the list, we also record them so that we can go back to them later 03:50
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pmichaud externally, someone using an array doesn't know that it has lazy portions -- conceptually the array looks as though it is "eager" 03:52
perigrin it's actually a pair (or more) of lists
one a vector of indicies
that enumerates the second
vamped perigrin: that's what I was thinking but couldn't put it to english.
pmichaud that's not the way I see it
an array contains things we've already enumerated, and lists that we've yet to enumerate 03:53
if we ask an array for something beyond the set of things we've already enumerated, it starts using its lazy lists to fill out the enumerated sequence until we get to what we're looking for 03:54
perigrin hmm 03:56
"yes" but I think that misses something that I'm not sure you care about since I missed the context
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vamped so 1,2,3,4..10 contains both an array (1,2,3) and a list (range 4..10) ? 03:57
pmichaud vamped: if you're looking at it as perl code, that's still a parcel 03:58
it's a parcel with a 1, a 2, a 3, and a range 4..10
but let's look at it this way:
my @a = 1,2,3,4..*;
internally, @a ends up with enumerated items 1, 2, and 3 (at indexes 0, 1 and 2) and an "unenumerated" range of 4..* 04:00
if we ask for @a[7], then the array internally starts iterating over its unenumerated list to add elements to its enumerated list until it reaches the one at index 7 04:01
let's rephrase that without the word "iterating" 04:02
so
if we ask for @a[7], then the array internally grabs new items from its unenumerated list(s) and adds them to the enumerated sequence until it's able to fulfill the request for the element at index 7. 04:03
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pmichaud anyway, the fundamental idea for me is that "lazy list" really means the same thing as "iterator" 04:04
vamped ok. and I assume we want the enumeration to be uni-directional -- indexing starting at 0 (more)
pmichaud and "array" is "a list where we remember the entire sequence of elements"
vamped @a=1..10000,6,7; so it will not be possible to access @a[*-1] without filling in 10000 missing pieces ?
pmichaud vamped: probably not, since *-1 in this case depends on knowing the last index (more) 04:05
perigrin pmichaud: except you just said you dont' remember the entire sequence, just the ones enumerated "so far" :)
pmichaud we remember the ones enumerated so far, and the lists that can tell us how to get to the remaining items in the sequence
(an array contains enumerated items and unenumerated lists) 04:06
vamped: I suppose it may be possible at some point to enumerate things at both ends, however.
that's likely to be a future feature, though. 04:07
vamped it seems plausible from a lay-man standpoint anyway. anyway your mental model is looking good to me.
pmichaud well, I'm also writing this for people who might read backscroll a bit later :) 04:08
(and to have a record of what I was thinking on my walk)
I'm also thinking it's feasible for a list to be Positional
what happens in that case is that the list uses itself to build an array, responds to the positional request(s), and then drops the array 04:09
so that @b.map( { ... } ).[5,7,3] works
essentially, postcircumfix:<[ ]> on a list simply does it work on a temporary array 04:10
perigrin pmichaud: mind if I present a slightly different take on it?
pmichaud not at all
perigrin a lazy list is the output of a function with a null signature 04:11
that is the same thing as an "iterator" ... it simply provides a stream of values
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perigrin an array is then the output of a function with a single element signature (the index) 04:12
well a "hash"
an array in Perl terms is then a hash where the index is generated from a list of sequential integers 04:13
if you see what I mean
pmichaud sure
perigrin so (1,2,3,4..Inf) becomes a coroutine that returns 1 then 2 then 3 then 4 ... then evaluates the range to start generating further values 04:14
this means that when you get to an array
@foo[7] becomes something you could potentially calculate directly 04:15
rather than having to populate the entire list up to 7
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pmichaud that works in this specific case, but not in the general case 04:15
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pmichaud we don't always know the number of elements a given iterator will produce 04:15
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pmichaud so if I have 04:15
perigrin yes
pmichaud (1,2,3, ..iterator.., 7, 8, 9) 04:16
and I ask for @foo[7]
I can't really find out where to jump without going through the iterator
perigrin (1,2,3,4..Inf,7,8,9) is a good example because the middle is incalcuably large
pmichaud oh, but in that case I can still easily jump to 7 04:17
because it clearly lands in the middle of the first iterator
the problem is when ..iterator.. might have a finite number of elements, but can't be known without actually stepping through them
for example, when reading from a filehandle
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pmichaud also, some iterators are destructive (such as filehandles) 04:18
and some iterators are expensive, such that you really want to store the results of what you've already computed rather than recomputing on each request
perigrin in those cases you *would* have to resort to calculating the value iteratively or recursively yes
you couldn't know what element was 7 until you knew what was 6 ... etc
until you got to a known start state
pmichaud right 04:19
perigrin it was just another way of illustrating the same concept
pmichaud right
one could conceivably come up with optimizations whereby finite lists don't have to be expanded in the enumerated section
(e.g., to save memory or computation time) 04:20
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pmichaud anyway, that summarizes why I think it's okay to be thinking of "list" as "iterator". Now to see if I can put it into implementable terms :) 04:22
later, though -- I'm going to take a break for a while.
perigrin there's some nice stuff in python with Generators I was looking at trying to grok corouteins 04:23
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diakopter tries to discern under which user jifty (commitbit) was running previously 05:05
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diakopter whee! 05:51
finally got commitbit back
commitbit.pugscode.org
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diakopter enjoy 05:51
diakopter out 05:52
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Su-Shee good morning 09:41
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colomon now? 11:21
this time for sure?
morning! 11:23
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colomon pmichaud: lists are always lazy feels right to me 11:27
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colomon so, hmmmm... do we need to be able to clone iterators? 11:33
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colomon HOP suggests defining a special $EXHAUSTED value to use as a sentinel instead of undef (our Nil) (page 168) 11:58
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colomon hmmm, HOP also defines a bunch of other possible interfaces. 12:26
but I think $EXHAUSTED may be the ticket for us. 12:27
it has that simple and correct feeling. 12:28
I think we will want TimToady's Iterable role, too. 12:31
So Any.list would become something like:
multi method list() { given self { when Iterator { return self; } when Iterable { return self.Iterator } default { return make_list(self); } } 12:33
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colomon where make_list takes a scalar and returns an iterator that returns that scalar. 12:34
of course, the right way to do this is using OO dispatch.
So role Iterator should define .list (which is just "return self"), and what I gave as Iterable.Iterator up there should actually be Iterable.list. 12:35
seems to me a bonus of all this is a bunch of very low-level p6 concepts can suddenly be implemented in p6 itself. 12:37
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pugs_svn r29581 | lwall++ | [Spec] random whackage on List, Seq, Parcel, Capture, Iterator, Nil etc. 13:59
r29581 | List is now simply the iterator role, and doesn't do Positional.
r29581 | Seq takes over Positional duties for reified (or reifiable) value lists.
r29581 | Think of Seq now as a constant Array (but also lazy like Array)
r29581 | Iterable now means you can ask for an iterator, but doesn't do List.
r29581 | Array, Seq, etc do Iterable, but not List. Only actual iterators do List.
r29581 | Nil is defined as a suitable sentinel for both list and slice iterators.
dalek kudo/ng: 8aedd0c | (Solomon Foster)++ | src/core/List.pm:
Start throwing iterator example code into List.pm. Compiles but not tested or used for anything.
 14:00
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colomon TimToady: you out there? 14:17
Doesn't Iterator have to be a mutable type? 14:19
that is, it has state, and that state has to change for the iterator to be useful. 14:25
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pugs_svn r29582 | lwall++ | [S02] some clarifications for colomon++ 14:44
colomon TimToady: :) 14:50
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vamped g'morning 15:01
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pmichaud good morning 15:01
oooh, spec updates! backscroll!
pmichaud reads
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colomon morning! 15:03
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pmichaud part of me wants "get the next element at the head of the list" to be .shift 15:05
colomon :) 15:07
vamped yes, in a way, the same. 15:08
pmichaud ouch, I'm not entirely happy with the new Seq. 15:09
(although I did consider something similar last night)
I'm not sure we need pushback/unshift on iterators. An iterator that does pushback/unshift is just an array. 15:11
colomon I like the idea that pushback / unshift are special Iterator roles, as in S07. It's easy enough to code an adaptor that turns a normal Iterator into either, after all... 15:18
pmichaud colomon: why? 15:19
I mean, if an iterator with pushback acts like an array, why not just use an array?
imo, the notion of pushback/unshift on an iterator comes from a time when we didn't have lazy arrays 15:20
colomon yeah, maybe? I guess if an array can be lazy, there is very little practical difference.
pmichaud so, pushback/unshift was a way of being able to put values into the iterator without forcing it to be eager, and we couldn't traditionally use an array for that because arrays were eager
colomon I guess part of the reason I like the idea of the special roles is that we can completely defer actually worrying about them. :) 15:21
pmichaud but now that our arrays are lazy.... it's trivial to have an array that is built from an iterator and supports the pushback/unshift semantics
in other words, we can now do: 15:22
my @a = $socket.lines;
and if we need to push something into the stream, we just use @a.unshift
colomon another point against the idea: it is trivial to implement using Iterator classes we're going to need anyway. 15:23
that is, we have to have an iterator class that has two iterators and does one, then the other.
pmichaud not so trivial, actually
it means that every iterator that implements .get also needs to have a way of checking its pushback array 15:24
colomon pmichaud: I'd argue that's the wrong approach.
pmichaud put another way, the more you work on the "trivial" implementation, I think you just discover that it is, in fact, the same as an array implementation
colomon that is, you take a normal array that implements .get without pushback, and add a buffer to implement pushback. that can be done with a simple class. though probably it has an array internally, for sure. 15:26
pmichaud but why do that?
what advantage does that give us over using an array?
colomon getting back on track, though, I think punting on pushback and unshift is appropriate for a first implementation.
pmichaud fair enough, I'm willing to punt for now
TimToady: I'm not comfortable with the idea that "list" creates a Seq 15:27
colomon because I don't see any advantage over an array other than I feel like I better understand how to implement it. :)
pmichaud in particular, I don't like the consequences of for list($a, $b, 1..10000, @c) { ... } 15:28
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pmichaud stated another way, I need a function/operator that performs list interpolation on its arguments without also imposing the "and remember everything you produce" semantic 15:29
(and I think "list" should be that function/operator) 15:30
if I want something to produce a Seq, it should be "Seq(...)" or "seq" or something like that. 15:31
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pmichaud oops, apologies -- I misread the diff 15:34
a list in item context becomes a Seq, not any list
okay, I think that's fine for me 15:35
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vamped pmichaud: back to .shift vs .get -- I think it is important to be consistent. if .get is the opposite of .unshift, then the two methods should either be (.shift and .unshift) or (.get and .put) 15:36
pmichaud vamped: perhaps, although I'd prefer not ".put" -- it has a different traditional meaning 15:37
in the C world, "put" tends to mean "write" and not "pushback"
but yes, shift/unshift seem more appropriate to me (more) 15:38
vamped perhaps, but in english it seems that get and put are opposites, as are shift and unshift.
pmichaud however, if we go with the idea that iterators don't implement pushback semantics, and only generate elements, then I'm okay with the idea that "get the next element" has a different name than "shift"
vamped wfm 15:39
pmichaud in general terms, I expect most people to be using "shift" (on an array) in order to deal with any sort of iterator
let's look at the implementation of map, for instance 15:40
or any function that wants to iterate over a list
sub map( &block, *@values ) { ... }
we probably want @values to be evaluated lazily here 15:41
we also don't want to keep each value hanging around after we're through with it, in case it happens to be a very long lazy list
so, we'd tend to do while (@values) { my $item = @values.shift; ... } 15:42
that way a call like map( { ... }, 1..1000000 ) doesn't end up creating a million-element array
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pmichaud so, internally the iterator can indeed have something like .get, but the way that most people will end up using it is with .shift 15:45
the same goes for lazy feeds 15:46
my @a <== $file.lines(); # lazy read of a file
while (@a) { $line = @a.shift; ... }
and if we want to push something back into the 'iterator', we end up doing unshift on the array, not on the list returned by $file.lines() (which we don't have access to anyway) 15:47
jnthn drops by 15:48
pmichaud: Last bits sound sane to me, fwiw. :-)
pmichaud greetings, jnthn. the world changed again. :-)
jnthn pmichaud: oh noes! 15:49
pmichaud: :-)
pmichaud: What should I read for latest?
15:49 Psyche^ joined
pmichaud r29851 diff, mainly 15:50
er, 29581
(transpose)
jnthn wow, that's a biggy.
colomon will be in and out all day -- in-laws down to help clean again 15:52
pmichaud "An iterator
+can never return C<Nil> as an ordinary value, so it is the sentinel
+value that marks the end of iteration.
...for some reason that sets off alarm bells to me.
(It didn't last night, but it does this morning) 15:53
jnthn Yes, I would prefer that out of band too.
pmichaud no, it's not that so much.
it's just that I can imagine an iterator returning Nil at some point.
but maybe not. 15:54
speculating:
my $c = \(1, 2, (), 4);
my $d = $c[2]; # $c[2] is Nil 15:55
15:55 Patterner left
pmichaud for @$c { ... } # only iterates over three elements -- skips the Nil element? 15:55
15:56 Psyche^ left
colomon I believe that's what TimToady has been saying, yes. 15:56
15:56 Patterner joined
pmichaud just seems weird that the capture would have something at index 2 but an iterator would always skip over it. 15:56
colomon personally I still like the idea of a sentinel value instead of Nil, a special constant we set up.
(and pity the fool who wants to return that constant from an iterator for some reason) 15:57
jnthn A Failure of some kind.
pmichaud well, we could have a constant that we check for by its .WHICH value
colomon Though another notion I had was if you wanted to return Nil from an iterator, you needed to create a special NilIterator value and return it. (NilIterator being the iterator that is always done.) 15:58
colomon goes back to boxing 15:59
15:59 am0c left
pmichaud or perhaps in the case of my $c = \(1, 2, (), 4); the () gets itemized into an empty Seq or something. 15:59
16:00 payload left
pmichaud although that can't be right, because Nil is supposed to itemize into an undef of somes ort 16:01
*some sort
jnthn +When it runs out of items, it will return C<Nil>. List context
+always removes C<Nil> values as part of flattening, while slice
+context always promotes parcels to C<Seq>, so it is never possible
+for this method to return C<Nil> as a value. We can use C<Nil> as
+the sentinel because iterators never return C<Parcel>s. and C<Nil>
+is defined as the empty C<Parcel>.
Is that saying that Nil can never happen anyway?
pmichaud in the case of my $c = \(1, 2, (), 4); we're not in list context.
although maybe @$c implies that we are in list context. 16:02
jnthn Yeah
I think so.
pmichaud but then, what to do with...
for (@$c).kv { ... }
because after the Nil element, the indices no longer match up :-) 16:03
jnthn But doesn't the list context make the () disappear? 16:04
pmichaud what list context?
jnthn Because it flattens the list?
The one implied by that @ there.
pmichaud sure
jnthn So by the time .kv sees it the () is no more
Oh, unless you're saying that's the problem. :-)
pmichaud I'm saying that's the problem.
jnthn Ah.
OK
I didn't consider it a problem. ;-) 16:05
pmichaud for (@$c).keys { say $c[$_]; } # oops, we never see the 4
jnthn Just read through that diff...it looks sane.
Yeah, I see what you mean. Hm.
pmichaud I'm not sure I see the purpose of the Iterable role yet. 16:08
jnthn "I can ask for an iterator", iiuc.
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TimToady probably just means that .list works 16:08
pmichaud but .list works on everything, iiuc
jnthn role Iterable { method list() { ... } }
Well, yeah, if list is the thingy that enforces list context... :-/ 16:09
erm, if .list is, I mean.
pmichaud no, .list doesn't mean "list context". It means "object as a list"
TimToady Cool.list is a fallback, not a role-supplied method
Iterable means you can ask it for an iterator
pmichaud so..... 16:10
jnthn TimToady: What are the fallbacks in Cool meant to be dispatchable to?
pmichaud do we still have the case that (3).elems == 1 ?
TimToady yes, but that's also because of Cool's .elems, not because everything does Positional 16:11
pmichaud so, in the general case, ($x).elems could fail if $x isn't Cool ? 16:12
TimToady well, if that worries us, we can put that one into Any :)
pmichaud same for something like $y.join('xyz')
?
TimToady the listy ones might still be in Any rather than Cool 16:13
but maybe not
pmichaud ...and if that's the case, then I get to my question of ".list works on everything"
TimToady but not always for the same reason
pmichaud sure
but then I don't see what "Iterable" does, if it's purpose is to say ".list works" 16:14
TimToady it's a role, it means "I implement list" rather than relying on some fallback
it means "I care about visitation and can visit more than one thing" 16:15
pmichaud okay, I can accept that.
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TimToady the default is self-visitation, is all 16:15
colomon I still think the last big worry is copying iterators. 16:16
pmichaud wfm
colomon: what's an example of copying an iterator?
colomon my @a <== 1...100000; my @b = @a 16:17
?
pmichaud the second assignment is mostly eager, there.
it would end up reifying both @b and @a 16:18
colomon I've been thinking about the list operators I mucked about trying to implement earlier, and I'm trying to think of how to implement .... umm, is it xx now? ... using iterators.
maybe there isn't actually a use case for copying iterators and I'm worrying about nothing. 16:19
Any idea how often Lists get copied now?
pmichaud depends on what you mean by "now"
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colomon in master. 16:19
TimToady yes, "now" is what transactions are all about defining
pmichaud colomon: in master, we don't have laziness. So, always. :-) 16:20
colomon Certainly with the interface we're talking about now, we can naively copy iterators if we're working at iterator level, right? my $iter = $x.list; my $iter2 = $iter; 16:21
are we going to argue that shouldn't work?
pmichaud with the interface we're talking about now, $iter isn't an iterator, it's a Seq 16:22
because a list in item context becomes a Seq
TimToady you can still get at the underlying iterator if you need to
pmichaud in which case I'd say it's not a copy, but a reference 16:23
TimToady yes, and .get on one advances everyone's view
(in that case)
not saying that's necessarily good
biab &
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pmichaud colomon: in your example of my $iter2 = $iter, we end up with both $iter and $iter2 pointing to the same Seq 16:24
much like if I have my $a = [1,2,3]; my $b = $a;
$b isn't a copy of the array, it's the same array.
(and since it's the same Seq, we don't need to copy the iterator) 16:25
yes, we might need to have .clone on an iterator available; I'm just saying it doesn't seem to occur naturally
colomon Ah, I guess I don't understand how Seq is supposed to work yet. 16:30
pmichaud Seq is basically an immutable array, iiuc
colomon I think my issue is I don't understand when they come into existence.
pmichaud right now, whenever a list is used in item context
colomon then how do you ever manage to work with the iterator itself? 16:31
pmichaud that's kind of the point -- you don't need to.
+Types that do the C<List> role are generally hidden from casual view, 16:32
+since iteration is typically triggered by context rather than by
+explicit call to the iterator's C<.get> method. Filehandles are a
+notable exception.
diakopter O_O
colomon but you do need to work with it to implement iterator support!
pmichaud if you're asking "how does one get an iterator", I think it's via the .Iterator (or .iterator) method 16:33
(haven't read the updated spec for that)
colomon ah, I thought the whole point of .list was it returned the iterator. 16:34
pmichaud no, .list returns something that iterates
you don't do .get on the thing returned by .list
the thing that is returned by .list does the .gets for you
vamped i think it's conceivable that one might want to copy an iterator, where when one changes it does NOT change the other. 16:35
pmichaud vamped: sure, that'd be .clone
vamped ok. so @a = @b.clone ?
pmichaud no, because @b isn't an iterator 16:36
TimToady I have no idea what that means on a lazy iterator
pmichaud and right, cloning a lazy iterator (e.g., on a filehandle) doesn't always make sense
so .clone is very iterator specific
colomon pmichaud: this thing that .list returns -- how does it know when it needs to .get ? I don't understand how it is different in concept from an iterator.
pmichaud colomon: it knows based on when you use it 16:37
essentially, it does the .get when you ask for an element
colomon I'm not crazy here, though, right? I mean, isn't "asking for an element" exactly the same in concept as calling .get? Why have two different interfaces to do this? 16:38
pmichaud look at it this way 16:39
suppose we have an iterator
let's call it $iter
what happens with for $iter { ... } ?
one thing that we know is that it _doesn't_ iterate the iterator here 16:40
if we want to do that, we have to do
for $iter.list { ... }
ehh, this is a icky example
never mind 16:41
the main difference is that .list returns us the result of iterating an iterator
my $a = @a.iterator; # $a is an Iterator 16:42
my $a = @a.list; # $a is a Seq
colomon is that just a difference in semantics, then? ie I've been imagining that the method name was .list, but it's actually .iterator? 16:44
pmichaud they're in fact different results 16:45
colomon wait, I can almost see it with the for example.
pmichaud maybe this helps:
my @a = 1..10;
my @b = @a.list;
my @c = @a.iterator;
how many elements does @b have?
how many elements does @c have? 16:46
colomon should that be $c instead?
pmichaud no, @c
colomon in my admittedly broken understanding, I'd think @b has 10 elements and @c has one. 16:47
pmichaud correct.
and that's why .list doesn't return an iterator
it returns something that does the iteration
colomon which is in fact a Seq?
pmichaud s/does/drives/
no, it's not a seq, unless placed into item context 16:48
jnthn gotta go again, will backlog
pmichaud a seq remembers all of the values of the iteration. in general we don't want to do that
colomon right.
Juerd Does my @b = @a.list make @b lazy, or do you need := for that? 16:49
pmichaud Juerd: you want <== for that
my @b <== 1..10000; # forces laziness
colomon my head's going in circles now, and I need to run downstairs and try to figure out why my server is no longer talking to my LAN. but I will keep pondering this.
pmichaud one can also do my @b = lazy @a 16:50
Juerd Hmm
vamped so, we can't do $c = @a.iterator ?
pmichaud (I think, if the 'lazy' keyword still exists)
Juerd lazy as a keyword on the LHS looks wrong
pmichaud vamped: you *can* do $c = @a.iterator -- that gives you the iterator itself instead of the results of the iteration
Juerd s/L/R/
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pmichaud Juerd: arrays are inherently lazy, but list assignment is "mostly eager" 16:51
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pmichaud here's a question (for TimToady) 16:55
what about something like
my @b = @a.map( { ... } );
assuming @a is finite, does the assignment take place eagerly? and how does it know? 16:56
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pmichaud feels like we'll need a way for lists and/or iterators to be able to say "I can still give you 'mostly eager' elements" 16:59
(and it has to be transitive)
17:01 vamped left
pmichaud does that sound correct-ish? 17:02
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TimToady nodnod 17:03
TimToady will be very distracted today; scorekeeping for four simultaneous quizzes...
pmichaud that's fine, I'm just trying to publicly plow our collective path through this :-)
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colomon pmichaud: I've briefly wondered if the "I can give you mostly eager" thing ought to be a role. subrole? 17:08
colomon doesn't have a solid feel for how to design "class" hierarchies in the role-enabled world.... 17:09
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TimToady probably more like: I do/don't know whether I'm finite/infinite 17:17
or .estimate_available that can return a number, or Inf, or * 17:18
where the estimate might or might not be terribly accurate, but would be good for an initial allocation in the destination
so a filehandle might guess at the number of lines in a file 17:19
but a RangeIterator knows exactly how many it has
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pmichaud TimToady: yes, I was thinking a similar thing on my walk. Something like .finity which returns the number of items the iterator believes it can cheaply/easily produce 17:35
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cono perl6: ([/]1..3).perl.say 18:35
p6eval pugs: *** ␤ Unexpected "1"␤ expecting dot, ":", "(", term postfix, operator or ")"␤ at /tmp/TAIUUosfeX line 1, column 5␤
..elf 29582: Parse error in: /tmp/iJkQFQeiLU␤panic at line 1 column 3 (pos 3): Error in quotesnabber␤WHERE: ([/]1..3).perl.say␤WHERE: /\<-- HERE␤ STD_red/prelude.rb:99:in `panic'␤ STD_red/std.rb:1311:in `quotesnabber'␤ (eval):1:in `__quote_8917700'␤ STD_red/prelude.rb:406:in `block in
..longest_to…
..rakudo 1d4928: 1/6␤
cono perl6: ([/]<1 2 3>).perl.say
18:35 nbrown left
p6eval pugs: *** reduce is nonsensical for /␤ at /tmp/Us9xavH8QO line 1, column 2-12␤ 18:35
..rakudo 1d4928: 0.166666666666667␤
..elf 29582: Parse error in: /tmp/I2jceo5GQr␤panic at line 1 column 3 (pos 3): Error in quotesnabber␤WHERE: ([/]<1 2 3>).perl.say␤WHERE: /\<-- HERE␤ STD_red/prelude.rb:99:in `panic'␤ STD_red/std.rb:1311:in `quotesnabber'␤ (eval):1:in `__quote_4321818'␤ STD_red/prelude.rb:406:in `block in
..longest…
cono Why it have a difference? 18:36
k23z__ www.itu.dk/~kbilsted/ALB.jpg 18:51
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colomon oh, hey. 20:26
ng: say 1/3;
p6eval ng 9c9e28: Method 'clone' not found for invocant of class 'Perl6MultiSub'␤current instr.: 'perl6;Iterator[];_block8346' pc 278469 (src/gen/core.pir:32580)␤
colomon ummm.... that's not the bug I was looking for. 20:27
that appears to be a fresh new bug?
oh, crap, did I do that this morning?
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colomon I'm kind of concerned that no one noticed this before now.... 20:32
cono colomon: what is ng ? 20:35
pmichaud ng is the active development branch of rakudo
cono rakudo: say 1/3;
TimToady cono: a reduce operator is a list operator, and therefore requires a space before the first argument
p6eval rakudo 1d4928: 0.333333333333333␤
TimToady std: [/]<1,2,3> 20:36
p6eval std 29582: ok 00:01 108m␤
TimToady that's parsing as ([/])<1,2,3>
not that , makes sense inside a <> subscript 20:37
std: [/] 1,2,3 # this is better
p6eval std 29582: ok 00:01 107m␤
TimToady perl6: say [/] 1,2,3
p6eval pugs: 0.1666666666666666666666666666666666666667␤
..elf 29582: Parse error in: /tmp/LFT7avJGII␤panic at line 1 column 6 (pos 6): Error in quotesnabber␤WHERE: say [/] 1,2,3␤WHERE: /\<-- HERE␤ STD_red/prelude.rb:99:in `panic'␤ STD_red/std.rb:1311:in `quotesnabber'␤ (eval):1:in `__quote_4544362'␤ STD_red/prelude.rb:406:in `block in
..longest_toke…
..rakudo 1d4928: 0.166666666666667␤
cono but why not a 1/6 ? 20:38
I asked .perl.say
dalek kudo/ng: 9174831 | (Solomon Foster)++ | src/core/List.pm:
Revert "Start throwing iterator example code into List.pm. Compiles but not tested or used for anything." because it appears to break ng badly.
TimToady because a Rat stringifies via Num
perl6: say ([/] 1,2,3).perl
p6eval pugs, rakudo 1d4928: 1/6␤
..elf 29582: Parse error in: /tmp/KsaaG0zhSM␤panic at line 1 column 7 (pos 7): Error in quotesnabber␤WHERE: say ([/] 1,2,3).perl␤WHERE: /\<-- HERE␤ STD_red/prelude.rb:99:in `panic'␤ STD_red/std.rb:1311:in `quotesnabber'␤ (eval):1:in `__quote_6628927'␤ STD_red/prelude.rb:406:in `block in
..long…
TimToady there's your 1/6 20:39
cono rakudo: say ([/] <1 2 3>).perl
p6eval rakudo 1d4928: 0.166666666666667␤
pmichaud rakudo (the old version) isn't up-to-date on Rats
afk -- going to lunch and to think about iterators a while
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cono rakudo: ([/] <1 2 3>).WHAT.say 20:41
p6eval rakudo 1d4928: Num()␤
cono rakudo: ([/] 1,2,3).WHAT.say
p6eval rakudo 1d4928: Rat()␤
cono ah
TimToady rakudo: for <1 2 3> { .WHAT.say } 20:45
p6eval rakudo 1d4928: Str()␤Str()␤Str()␤
cono Str -> Num 20:46
I think, I got it :D
TimToady that's specced to return Int Int Int someday
cono TimToady: ty :)
Does rakudo have something like . in haskell ? 20:52
colomon cono: sorry for disappearing there, phone call. I see pmichaud answered your question. 20:56
what is . in haskell?
ng: say 1/3
p6eval ng 917483: 0.333333333333333␤
cono something like concatenating of functional types 20:57
colomon ng: my $a = 0.333333333333333
p6eval ng 917483: ( no output )
cono colomon: [ .Int . / ] <1 2 3> => must produce 1/6 Rat
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colomon I don't believe perl 6 has a function composition operator (if that's what you mean) 20:59
cono colomon: yeah, sorry, have a bad english :)
you are right
colomon rakudo: say ([/] (1, 2, 3)).perl 21:00
p6eval rakudo 1d4928: 1/6␤
cono rakudo: ([/]1,2,3).perl.say
p6eval rakudo 1d4928: 1/6␤
cono golf it :D
colomon yeah, I'm still not completely comfortable leaving off the ( )s around my lists. :)
cono :) 21:01
colomon anyway, as you can see, the example works fine in Rakudo (master) as long it's clear the type of the numbers is Int.
cono yeah, %h = 1 => 2 ... different than p5
colomon I don't think [ ] is implemented yet in Rakudo ng.
cono problem was with <1 2 3> 21:02
coz it have Str inside
aesop whats %h = 1 => 2 in perl 6
cono rakudo: my %h = 1 => 2; %h.perl.say 21:03
p6eval rakudo 1d4928: ( no output )
colomon cono: right
cono at local version i have: {"1" => 2} 21:04
ng: my %h = 1 => 2; %h.perl.say
p6eval ng 917483: Confused at line 1, near "my %h = 1 "␤current instr.: 'perl6;HLL;Grammar;panic' pc 500 (src/stage0/HLL-s0.pir:328)␤
cono std: my %h = 1 => 2; %h.perl.say
p6eval std 29582: ok 00:01 109m␤
colomon Hashes are currently on the ng to-do list. 21:05
cono ic
ng: say $*PERL
p6eval ng 917483: ␤
cono rakudo: say $*PERL
p6eval rakudo 1d4928: Contextual $*PERL not found␤␤
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TimToady std: ([/]1,2,3).perl.say 21:11
p6eval std 29582: ===SORRY!===␤Two terms in a row at /tmp/B5j5a7X8X8 line 1:␤------> ([/]⏏1,2,3).perl.say␤ expecting any of:␤ POST␤ bracketed infix␤ infix or meta-infix␤ postfix␤ postfix_prefix_meta_operator␤
..prefix_circumfix_meta_operator__S_258reduce␤ prefix_postfi…
21:11 jjore joined
frettled Hm, what was that supposed to be? 21:12
TimToady std: ([/] 1,2,3).perl.say
p6eval std 29582: ok 00:01 107m␤
TimToady STD requires the space there 21:13
cono rakudo - not
:)
TimToady std: [/]
p6eval std 29582: ok 00:01 105m␤
TimToady rakudo: [/]
p6eval rakudo 1d4928: Syntax error at line 2, near "[/]"␤in Main (file <unknown>, line <unknown>)␤
TimToady STD is correct there too 21:14
rakudo: say [/]()
p6eval rakudo 1d4928: Use of uninitialized value␤␤
TimToady rakudo: say [*]()
p6eval rakudo 1d4928: 1␤
TimToady rakudo: say [+]()
p6eval rakudo 1d4928: 0␤
21:15 am0c joined
frettled *lights up* - aha 21:15
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cono why [*]() produce 1 ? 21:15
TimToady [/] without a space or () is parsed as not having any args
(in STD) 21:16
std: print
p6eval std 29582: Potential difficulties:␤ Unsupported use of bare 'print'; in Perl 6 please use .print if you want to print $_, or use an explicit argument at /tmp/CoRwdQef0X line 1:␤------> print⏏<EOL>␤ok 00:01 105m␤
TimToady std: print()
p6eval std 29582: ok 00:01 105m␤
21:17 payload1 joined
TimToady could force reduction ops to follow a similar policy 21:17
cono can i combine two operators in [] ?
TimToady no
cono three? 21:18
joking? :)
frettled You'd have to specify your own infix operator that combined them. :)
infix? why did I write infix?
TimToady I presume cono wishes to alternate operators
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cono I just wanted to force Int type casting 21:21
rakudo: ([/] <1 2 3>.map({ $_.Int })).perl.say
p6eval rakudo 1d4928: 1/6␤
cono or something like ([Int . /] <1 2 3>).perl.say :) 21:22
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cono rakudo: ([\/] map {.Int}, <1 2 3>).perl.say 21:38
p6eval rakudo 1d4928: Syntax error at line 2, near "([\\/] map "␤in Main (file <unknown>, line <unknown>)␤
cono std: ([\/] map {.Int}, <1 2 3>).perl.say
p6eval std 29582: ok 00:01 109m␤
colomon rakudo; <1 2 3>>>.Int.perl.say 21:40
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colomon rakudo: <1 2 3>>>.Int.perl.say 21:41
p6eval rakudo 1d4928: [1, 2, 3]␤
21:41 jferrero joined
colomon rakudo: say [/] <1 2 3>>>.Int 21:42
p6eval rakudo 1d4928: 0.166666666666667␤
21:42 snearch joined
colomon or if you will 21:42
frettled I think this is one case where the Unicode version is more readable: <1 2 3>».Int
colomon rakudo: ([/] <1 2 3>».Int).perl.say 21:43
p6eval rakudo 1d4928: 1/6␤
cono std: <1 2 3>>>.Int.reduce(&infix:</>).perl.say
p6eval std 29582: ok 00:01 128m␤
cono rakudo: <1 2 3>>>.Int.reduce(&infix:</>).perl.say
p6eval rakudo 1d4928: Unknown introspection value 'pos_required'␤in Main (file <unknown>, line <unknown>)␤
cono ng: <1 2 3>>>.Int.reduce(&infix:</>).perl.say 21:44
p6eval ng 917483: Symbol '&infix:</>' not predeclared in <anonymous>␤current instr.: 'perl6;PCT;HLLCompiler;panic' pc 137 (src/PCT/HLLCompiler.pir:101)␤
aesop owned
colomon ng doesn't have reduce yet, either. 21:45
ng: say <1 2 3>.perl
p6eval ng 917483: ("1", "2", "3")␤
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cono moritz_: Your articles are great! Thanks :) 21:48
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pmichaud back again, for a bit 21:57
frettled And there was much rejoicing. 22:04
pmichaud: how's ng coming along?
pmichaud well, we're having to rethink lists and iterators a fair bit
frettled oh? 22:07
colomon frettled: Today's spec changes are a side-effect. 22:20
frettled aha
colomon I think the easiest summery is that we (pmichaud mostly) realized that the idea of Lists as immutable Arrays didn't really sit well with the idea of Lists as things generated by Iterators. 22:21
It caused a bunch of overhead for common cases where you didn't actually care about anything but using what the Iterator was generating right away. 22:22
So now Lists are just iterators (more or less) and there's another type (Seq) to make a List look more like an Array if needed. 22:23
I think -- I admit I'm still fuzzy on some of the details. 22:24
pmichaud there was already a Seq before, too -- but now it's different :)
frettled The battle plan (spec) didn't survive contact with the enemy (implementation). :D 22:25
pmichaud that's happened a few times now :)
frettled yep, and I think that's good
colomon pmichaud: are you ready to try implementing the new spec? it feels to me like it is time to implement and figure out what doesn't work about the current ideas in practice... but then, I'm not doing the core of the work. :) 22:27
pmichaud colomon: the new spec means we have to re-do all of Parcel as well.
it's not just a matter of writing "class Iterator ..." and being done 22:28
colomon ay ay ay!
pmichaud or put another way -- the new "spec" is still incomplete
colomon oh, I understand that, because there's still that magic thing .list returns that I don't understand very well. :)
frettled masak will be so pleased when he's back from his sabattical :D
pmichaud well, I'm currently toying with the idea of ParcelIterator
frettled Hrms, my browser doesn't want to be my friend right now, so I don't get to look at the spec changes. *grumblesmurf* 22:29
pmichaud which may in fact end up being "List"
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frettled at first glance, that may simplify things 22:29
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