$ cat foo.pl
my %a;
$_='fOo';

$a{lc}++;
$a{lc()}++;
$a{+lc}++;
$a{lc,}++;

$ perl -MO=Deparse foo.pl
my %a;
$_ = 'fOo';
++$a{'lc'};
++$a{lc $_};
++$a{lc $_};
++$a{lc $_};
foo.pl syntax OK