#!/usr/local/bin/perl 

sub add {
    return $_[0] + $_[1];
}

sub result {
    my $sum = shift;
    $sum = add($sum, shift) while @_;
    return $sum;
}

print result(@ARGV);

##</code><code>##

$ PERLDB_OPTS="NonStop AutoTrace frame=29" perl -d ./silly.pl 2 3 4
Package ./silly.pl.
13:     print result(@ARGV);
in  @=main::result(2, 3, 4) from ./silly.pl:13
 8:         my $sum = shift;
 9:         $sum = add($sum, shift) while @_;
 in  $=main::add(2, 3) from ./silly.pl:9
  4:        return $_[0] + $_[1];
 scalar context return from main::add: 5
 in  $=main::add(5, 4) from ./silly.pl:9
  4:        return $_[0] + $_[1];
 scalar context return from main::add: 9
 10:        return $sum;
list context return from main::result:
0  9
9