Re: [pugs]weird thing with say ++$

On 21 Apr, fayland wrote:

: It has been published at perl6.language, but have no reply.

That was to be expected, as it's no language-design specific issue,
and therefore, unsuitable for p6l.


: In perl v5.8.6 built for MSWin32-x86-multi-thread:
: 
: my $i = 1;
: print $i++, ++$i; # 1 3
: my $i = 1;
: print ++$i, $i++; # 3 2

You're misleaded here, by thinking, scalar context is being enforced,
which is not the case; the results of the increment operator operations (ops) 
on the scalar are being passed in (implicit) array context to the print builtin.

Every Perl program, that gets compiled and interpreted, will be
converted to a syntax tree initially. The following is a selected excerpt
from the output of the core module B::Terse, which displays, what syntax
tree we actually got hold of.

    LISTOP (0x3c013760) print 
        OP (0x3c013780) pushmark 
        UNOP (0x3c013700) postinc [2] 
            OP (0x3c0136e0) padsv [1] 
        UNOP (0x3c013740) preinc 
            OP (0x3c013720) padsv [1]

So, LISTOP indicates, that a list context is being encountered, which is
not, what we actually want. The syntax trees for the two examples,
provided above, don't differ that much, except, as you'd assume, in case
of the ordering of the UNOPs. I don't see any way to explain, what's
going wrong *exactly* by examining the syntax tree; that'd require
digging into the internals, I'd assume.


        my $i = 1;
        
and either

        print $i++; print ++$i;
or
        print ++$i; print $i++;


does what you assumed, it was supposed to do, but without
having the compiler struggling against implicit assumptions.


: in pugs:
: 
: my $i = 1;
: say $i++, ++$i; # 1 3
: 
: my $i = 1;
: say ++$i, $i++; # 2 2

This leads me to think, Pugs has implemented the behaviour, that has
been outlayed in Apocalypse 03: Operators, RFC 082 - Arrays: Apply
operators element-wise in a list context,
http://dev.perl.org/perl6/doc/design/apo/A03.html


: which is right?(I think perl5 is) or it's different between Perl5 and
Perl6?

I'm not inclined to think, that Perl 5 is wrong here, as letting it
assume array context, is in this context, like assuming, filling your
fridge with food, it consists of, by randomly throwing some of it in,
will come out sorted again; Perl 6 does, what the specifications urge
upon it to do.

 
: /Fayland Lam/

Steven