package MyConstants;

use strict;
use warnings;

require Exporter; # you may use other exporter modules
our @EXPORT; # empty by now

use constant FOO => 1;
use constant BOO => 2;
use constant BAR => 3;
# ...

#### here begins the code to find and populate the list of exports with constant names

our @GLOBAL_SYMBOLS; # these are not package constants, but Perl artifacts
BEGIN {
    @GLOBAL_SYMBOLS = qw(BEGIN EXPORT);
}

# $ans = is_constant($symbol_name);
#
# decides if a name is a package constant or not.
# Checks if it is all upper-case and not in @GLOBAL_SYMBOLS
sub is_constant {
    my $k = shift;
   return $k =~ /^[A-Z]+$/ 
       && !grep { $_ eq $k } @GLOBAL_SYMBOLS
}

# push_constants(\@export, @symbols)
#
# Push @symbol names into @export if they satisfy is_constant
sub push_constants {
    my $export_ref = shift;
    my @symbols = @_;
    for my $s (@_) {
        if ( is_constant($s) ) {
            #print "s: $s\n";
            push @$export_ref, $s
        }
    }
}

BEGIN {

    # iterate the package stash
    my @keys = do { no strict 'refs'; keys %{__PACKAGE__ . '::'} };
    push_constants(\@EXPORT, @keys);

}

print "export: @EXPORT\n";

#### here ends the code to find and populate the list of exports with constant names

1;