Maybe you need something even older?

I'm quite surprised. I used ActivePerl 5.6.0 back then, but I don't think that the distribution would make any difference. Maybe I'm just mixing this up with something closely related.

perl561delta agrees with me though that ...

<Reveal this spoiler or all in this thread>

Could you provide B::Deparse output of your code for 5.6.0 and 5.6.1? B::Deparse had plenty issues of its own back then, but it will probably be interesting.

lodin

Sure thing. I include a optree dump too (Terse for 5.6.0 since Concise wasn't found.)

(I emptied the body for terseness after making sure it didn't affect the result.)

5.6.0:

>c:\progs\perl560\bin\perl -v

This is perl, v5.6.0 built for MSWin32-x86-multi-thread
(with 1 registered patch, see perl -V for more detail)

Copyright 1987-2001, Larry Wall

Binary build 635 provided by ActiveState Corp. http://www.ActiveState.
+com
Built 15:34:21 Feb  4 2003

...

>c:\progs\perl560\bin\perl -MO=Deparse -e"for my $s ( qw( a b c ) ) {}
+"
foreach my $s ('a', 'b', 'c') {
    ();
}
-e syntax OK

>c:\progs\perl560\bin\perl -MO=Terse -e"for my $s ( qw( a b c ) ) {}"
LISTOP (0x184fcc4) leave [1]
    OP (0x184fca4) enter
    COP (0x184fd10) nextstate
    BINOP (0x184fd4c) leaveloop
        LOOP (0x1828b24) enteriter [1]
            OP (0x184ff6c) null [3]
            UNOP (0x184fe9c) null [141]
                OP (0x184fe7c) pushmark
                SVOP (0x184ff10) const  SPECIAL #0 Nullsv
                SVOP (0x184fec8) const  SPECIAL #0 Nullsv
                SVOP (0x184fe48) const  SPECIAL #0 Nullsv
        UNOP (0x184fd74) null
            LOGOP (0x184fd98) and
                OP (0x1828b8c) iter
                LISTOP (0x184fdc0) lineseq
                    OP (0x184fe28) stub
                    OP (0x1828b6c) unstack
                    COP (0x184fdec) nextstate
-e syntax OK
[download]

5.6.1:

>c:\progs\perl561\bin\perl -v

This is perl, v5.6.1 built for MSWin32-x86-multi-thread
(with 1 registered patch, see perl -V for more detail)

Copyright 1987-2001, Larry Wall

Binary build 635 provided by ActiveState Corp. http://www.ActiveState.
+com
Built 15:34:21 Feb  4 2003

...

>c:\progs\perl561\bin\perl -MO=Deparse -e"for my $s ( qw( a b c ) ) {}
+"
foreach my $s ('a', 'b', 'c') {
    ();
}
-e syntax OK

>c:\progs\perl561\bin\perl -MO=Concise -e"for my $s ( qw( a b c ) ) {}
+"
e  <@> leave[$s:5,7] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 7 -e:1) v ->3
d     <2> leaveloop vK/2 ->e
7        <{> enteriter(next->9 last->d redo->8)[$s:5,7] lK ->b
-           <0> ex-pushmark s ->3
-           <1> ex-list lKPM ->7
3              <0> pushmark sM ->4
4              <$> const(SPECIAL Null)[t2] sM ->5
5              <$> const(SPECIAL Null)[t3] sM ->6
6              <$> const(SPECIAL Null)[t4] sM ->7
-        <1> null vK/1 ->d
c           <|> and(other->8) vK/1 ->d
b              <0> iter s ->c
-              <@> lineseq vK ->-
8                 <0> stub v ->9
9                 <0> unstack v ->a
a                 <;> nextstate(main 7 -e:1) v ->b
-e syntax OK
[download]

A quick look at the docs shows that qw-as-a-list has been around since 5.6.0.