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• For the record :) (Score:2)

  by Juerd (1796) on 2005.04.20 16:49 (#39864) Homepage

  I was unaware of the current implementation and only explained how I think things are meant. It was not my intention to delay the release -- Sorry, folks! :)
  
  And for outsiders who want to know what we're talking about (I can imagine it's all very vague and hard to follow if you "weren't there"), the IRC log with lines about other topics removed:
  
  (All IRC timestamps are approximately UTC+0202)

  22:13 < autrijus> Juerd: hey, maybe you can answer this
  22:13 < autrijus> foo(1,2,3);
  22:13 < autrijus> foo(1,(2,3));
  22:13 < autrijus> foo((1,2,3));
  22:13 < autrijus> they are potentially different things, right?
  22:13 < autrijus> not always the same
  22:15 < Juerd> autrijus: Depends on foo's signature, I think
  22:15 < autrijus> Juerd: right.
  22:15 < Juerd> OTOH, no, I think they're all the same.
  22:15 < autrijus> Juerd: right.
  22:15 < autrijus> wait, you can't be right on both times.
  22:15 < Juerd> Or, wait, no, "," is a constructor now, isn't it? :)
  22:16 < autrijus> Juerd: you are confusing me :-/
  22:16 < autrijus> I'm already confused
  22:16 < Juerd> That'd mean they have to be different
  22:16 < Juerd> But they can't be, because non-subcall parens are only for
  forcing precedence
  22:16 < Juerd> HELP
  22:16 < Juerd> There are two similarly spelled operators, one being , and the
  22:16 < autrijus> *exactly*
  22:16 < Juerd> One separates sub call arguments, the other list elements
  22:16 < autrijus> right.
  22:17 < Juerd> Except of course when lexical (lexical as in how they appear in
  code) lists do flatten, regardless of context
  22:17 < Juerd> In which case everything matches up again
  22:17 < Juerd> In a most useful way :)
  22:17 < autrijus> so...
  22:17 < autrijus> is((1,2), (3,4), "hey");
  22:17 < autrijus> is this happy or not?
  22:18 < autrijus> assuming &is has the signature of <Str,Str,Str -> Str>
  22:18 < Juerd> No
  22:18 < Juerd> Oh
  22:18 < Juerd> What's ->?
  22:18 < autrijus> <Str,Str,Str -> Bool>, rather
  22:18 < autrijus> the return type
  22:18 < Juerd> And doesn't -> in <> clash?
  22:18 < autrijus> not something canonical ;)
  22:18 < autrijus> i.e. it's my notation, ignore it
  22:18 < Juerd> Oh!
  22:19 < Juerd> It has too many arguments, I think, autrijus
  22:19 < Juerd> Although
  22:19 < Juerd> Hm, no
  22:19 < Juerd> It's okay!
  22:19 < Juerd> Because the *,* is in scalar context, not the parens - they just
  group
  22:19 < Juerd> Yep, that must be it
  22:20 < autrijus> ok. I'm asking p6l :)
  22:20  * Juerd can be extremely confusing when he's thinking out loud
  22:20 < Juerd> autrijus: I think it's okay and equivalent to is([1,2], [3,4],
  "hey")

  Then, Autrijus sent his question to p6l, I answered it there according to my latest guess, and Larry confirmed that this guess was right:

  From: Larry Wall <larry@wall.org>
  Date: Wed, 20 Apr 2005 13:30:38 -0700
  To: perl6-language@perl.org
  Subject: Re: Quick question: parens vs subroutine parameter
   
  On Wed, Apr 20, 2005 at 10:23:14PM +0200, Juerd wrote:
  : Autrijus Tang skribis 2005-04-21  4:19 (+0800):
  : > So, following up on the Parens handling, are these two equivalent?
  : >     # Assuming &is has the parameter signature (Str, Str, Str)
  : >     is((1,2), (3,4), "hey");
  : >     is([1,2], [3,4], "hey");
  :
  : I think so.
  :
  : > What happens if &is is of type (Any, Any, Str)?
  :
  : Same thing, as the inner comma is still in scalar context.
  :
  : However, with list context, I expect things to flatten, so with a
  : signature of *@_, it puts 5 elements in @_.
   
  That's all correct.
   
  Larry

  We continued on IRC: (the time difference is caused by my driving home)

  23:08 < Juerd> autrijus: I eventually guessed correctly! ;)
  23:10 < autrijus> gah.
  23:10 < autrijus> Juerd: you are correct after all.
  23:10 < autrijus> Juerd: so if &is is of signature (Array, Array, Str)
  23:11 < autrijus> (all three nonslurpy)
  23:11 < autrijus> Juerd: is the inner (1,2) still running in scalar context?
  23:11 < autrijus> Juerd: or are the suddenly in Array context?
  23:11 < Juerd> autrijus: Then it's still scalar context (specifically, array
  context, which surprisingly nicely is not a form of list context) :)
  23:11 < Juerd> autrijus: Array context is a scalar context
  23:11 < autrijus> Juerd: that is hard to believe.
  23:12 < autrijus> Juerd: I can see "array ref" context, maybe
  23:12 < Juerd> I think we should rename scalar context to singular context
  23:12 < autrijus> Juerd: but Array is a List
  23:12 < autrijus> as Hash is a List
  23:12 < Juerd> autrijus: Array is a class, classes when used for context expect
  objects, objects are references, Array implies ref
  23:12 < Juerd> autrijus: That may be, but types have nothing to do with
  context.
  23:12 < autrijus> Juerd: wow. that line is the most clear thing I have read.
  23:13 < autrijus> Juerd: it also invalidates my hope to release 6.2.1 tonight
  :-(
  23:13 < autrijus> Juerd: since that means my Eval.hs comma implementation is
  All Wrong.
  23:13 < Juerd> autrijus: I think it'd be good to rename scalar and list context
  to singular and plural context, to avoid confusion with types.
  23:13 < autrijus> Juerd: so, it has nothing to do with types, right?
  23:13 < autrijus> it's either singular, or plural
  23:14 < autrijus> literal lists always flatten in plural context
  23:14 < autrijus> and never flatten in singular context
  23:14 < autrijus> singular context may be further limited in expecting specific
  object types
  23:14 < Juerd> autrijus: The main contexts have nothing to do with types,
  except that scalar(singular) context can expect a certain type of singular
  value, for example, an Array (reference)
  23:14 < autrijus> while plural context does not care about type
  23:14 < Juerd> autrijus: Exactly
  23:14 < autrijus> is that the case?
  23:15 < Juerd> autrijus: Plural context can care about the types of its values
  23:15 < autrijus> Juerd: I wish these lines are in the synopsis!
  23:15 < autrijus> Juerd: can you be kind and summarize these line into a reply
  on p6l to my thread?
  23:15 < autrijus> and get another "That's all correct" from Larry
  23:16 < autrijus> so, sorry, folks, no 6.2.1 tonight because the new context
  handling is all wrong :-/
  23:16 < Juerd> autrijus: Which lines precisely?
  23:16 < autrijus> Juerd: everything after
  23:16 < autrijus> 05:08 < autrijus> Juerd: you are correct after all.
  23:16 < Juerd> autrijus: That's a lot.
  23:16 < autrijus> Juerd: well, what you said, anyway
  23:16 < autrijus> I'd do that, but it's 5:14am here and my fingers are on
  strike :)
  23:16 < Juerd> I'll see if I can make a nice bulleted list
  23:17 < autrijus> thank you
  23:17 < autrijus> Juerd++
  23:19 < autrijus> is Void a special subtype of Singular, then?
  23:19 < autrijus> or is Void a context of its own like in p5?
  23:21 < autrijus> Nullar
  23:21 < autrijus> I'll need to sleep on this new revelation.
  23:21 < gaal> (i've seen "nullary" mentioned in some haskell texts, no doubt in
  different, er, contexts)
  23:22 < autrijus> gaal: it's used in arity context, so "unary" instead of
  "singular"
  23:22 < gaal> ah. the *opposite* of context.
  23:22 < gaal> (in a way.)
  23:23 < autrijus> :)
  23:23  * autrijus waves... I'll be back :)
  23:23 < gaal> night!
  23:23 < autrijus> see you tomorrow, folks
  23:23 < autrijus> night!
  23:23 < autrijus> &
  23:27 < Juerd> autrijus: I'd think void context would not be Void context, as
  you cannot have a reference to nothing, or express nothingness in a variable
  (we have undef), or meaningfully force void context in an expression

  See also the related thread "Quick question: parens vs subroutine parameter" in the perl6-language mailinglist.

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