Avoiding eval:

my @num_to_name;
BEGIN {
    @num_to_name = qw(FOO BAR);
    require constant;
    constant->import( $num_to_name[$_] => $_ ) for 0 .. $#num_to_name;
}
[download]

Avoiding eval and multiple calls to import:

my @num_to_name;
BEGIN {
    @num_to_name = qw(FOO BAR);
    require constant;
    constant->import({ map { $num_to_name[$_] => $_ } 0..$#num_to_name
+ });
}
[download]