S06: Pairs as lvalues

Hi,

quoting http://dev.perl.org/perl6/synopsis/S06.html:
> Pairs can be used as lvalues. The value of the pair is the
> recipient of the assignment:
> 
>     (key => $var) = "value";
> 
> When binding pairs, names can be used to "match up" lvalues
> and rvalues:
> 
>     (who => $name, why => $reason) := (why => $because, who => "me");

that's really convenient, but what will the following code do?
  my $x = (a => 42); # $x is a Pair.
  $x = 13;           # Is $x now the Pair (a => 13) or
                     #           the Int 13?

When executing the second line, $x is a Pair. And it is used as a
lvalue. So, according to S06, the assignment will only change the
value of the Pair, not the Pair itself.

But I doubt this is what most programmers will expect -- example:
  sub foo (Any $x) {
    $x = 13; # Won't always make $x an Int.
    ...;
  }
  my $pair = (a => 42);
  foo($pair);

So, does this Pairs-as-lvalue rule only affect "real syntax-Pairs"?
If not, what would the sub unpairify in the following code have to
look like?
  my $x = (a => 42);
  unpairify($x, 13);
  # $x is now the Int 13.

  sub unpairify (Any $x is rw, Int $num) {
    ...; # fill in please
  }

--Ingo

-- 
Linux, the choice of a GNU | self-reference, n. - See self-reference  
generation on a dual AMD-  | 
Athlon!                    | 

• S06: Pairs as lvalues by Ingo Blechschmidt
• Re: S06: Pairs as lvalues by Luke Palmer
• Re: S06: Pairs as lvalues by Ingo Blechschmidt
• Re: S06: Pairs as lvalues by Uri Guttman
• Re: S06: Pairs as lvalues by Ingo Blechschmidt