The third parameter, the input parameter list, specifies how many arguments the function wants, and their types. It MUST be passed as a list reference. The following forms are valid: [a, b, c, d] \@LIST #### my $arr = [ pack("d",1), pack("d",1.5), pack("d",3) ]; # or as I would do it... my $arr = [ map { pack 'd', $_ } ( 1, 1.5, 3 ) ]; #### my @arr = map { pack 'd', $_ } ( 1, 1.5, 3 );