$ perl5.12.5 -we'for my $k qw(a b) {$_=$k}'
$ perl5.14.0 -we'for my $k qw(a b) {$_=$k}'
Use of qw(...) as parentheses is deprecated at -e line 1.
$ perl5.16.3 -we'for my $k qw(a b) {$_=$k}'
Use of qw(...) as parentheses is deprecated at -e line 1.
$ $ perl5.18.0 -we'for my $k qw(a b) {$_=$k}'
syntax error at -e line 1, near "$k qw(a b)"
Execution of -e aborted due to compilation errors.

##</code><code>##

=head2 Use of qw(...) as parentheses

Historically the parser fooled itself into thinking that C<qw(...)> literals
were always enclosed in parentheses, and as a result you could sometimes omit
parentheses around them:

    for $x qw(a b c) { ... }

The parser no longer lies to itself in this way.  Wrap the list literal in
parentheses like this:

    for $x (qw(a b c)) { ... }

This is being deprecated because the parentheses in C<for $i (1,2,3) { ... }>
are not part of expression syntax.  They are part of the statement
syntax, with the C<for> statement wanting literal parentheses.
The synthetic parentheses that a C<qw> expression acquired were only
intended to be treated as part of expression syntax.

Note that this does not change the behaviour of cases like:

    use POSIX qw(setlocale localeconv);
    our @EXPORT = qw(foo bar baz);

where parentheses were never required around the expression.

##</code><code>##

=head2 qw(...) can no longer be used as parentheses

C<qw> lists used to fool the parser into thinking they were always
surrounded by parentheses.  This permitted some surprising constructions
such as C<foreach $x qw(a b c) {...}>, which should really be written
C<foreach $x (qw(a b c)) {...}>.  These would sometimes get the lexer into
the wrong state, so they didn't fully work, and the similar C<foreach qw(a
b c) {...}> that one might expect to be permitted never worked at all.

This side effect of C<qw> has now been abolished.  It has been deprecated
since Perl v5.13.11.  It is now necessary to use real parentheses
everywhere that the grammar calls for them.