if (ref $param) {
    # it isn't a simple string, assume it is a filehandle
    $fh = $param;
  } else {
    open $fh, "<", $param or die "$param: $!";
  }

##</code><code>##

  my $type = ref $param;
  if (!$type) {
    # it's a simple scalar
  } elsif ($type eq 'GLOB') {
    # an unblessed GLOB ref
  } elsif ($type eq 'IO::Handle') {
    # it's a non-overloaded IO::Handle
  } else { ... }

##</code><code>##

  if (!ref $param) {
    # scalar
  } elsif (ref($param) eq 'GLOB') {
    # GLOB
  } elsif ($param->isa('IO::Handle')) {
    # is, or inherits from, IO::Handle
  } else { ... }

##</code><code>##

  if (!ref $param) {
    # scalar
  } elsif ($param->can('readline')) {
    # who knows what it is? But it supports a readline method ...
  } else { ... }

##</code><code>##

  Can't locate method 'readline' via package 'IO::StrangeHandle'