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

[Steven Philip Schubiger]

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

[Juerd]

Steven Philip Schubiger skribis 2005-04-25 5:41 (+0200):

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

> : 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.

I don't know how it's called on other levels, but we're still calling
that list|slurpy|plural context. "array context" looks too much like
"Array context", which is something else.

In array context, @foo is passed as the array that it is. In
list context, it is flattened. Big and very important difference.

Juerd
--
http://convolution.nl/maak_juerd_blij.html
http://convolution.nl/make_juerd_happy.html
http://convolution.nl/gajigu_juerd_n.html

[Steven Philip Schubiger]

On 25 Apr, Juerd wrote:

: I don't know how it's called on other levels, but we're still calling

: that list|slurpy|plural context. "array context" looks too much like
: "Array context", which is something else.

I confess, it's likely a bad habit, to coin it "array context" on
p6l, although it refers to Perl 5, where it I have seen it more than
once - perhaps, overly abused too.

: In array context, @foo is passed as the array that it is. In

: list context, it is flattened. Big and very important difference.

You're supposedly right.

: Juerd

Steven

[Juerd]

Steven Philip Schubiger skribis 2005-04-25 18:44 (+0200):

> I confess, it's likely a bad habit, to coin it "array context" on
> p6l, although it refers to Perl 5, where it I have seen it more than
> once - perhaps, overly abused too.

That's old Perl5-ese. There was a big jargon change when people started
to realise and agree that having two things both called arrays or lists
was confusing. There are still some occurrences of "array context" left,
but in reality, even in Perl 5, that should only refer to the context in
which an array is expected, as provided by a \@ prototype.