sub type {
 my $obj = shift;

 return $obj->isa('HASH') ? 'HASH' :
  $obj->isa('ARRAY') ? 'ARRAY' :
  $obj->isa('SCALAR') ? 'SCALAR' :
  die 'Not HASH, ARRAY or SCALAR';
}

print type( bless \a ), "\n";
print type( bless [a] ), "\n";
print type( bless {a=>b} ), "\n";
print type( bless \*STDOUT ), "\n\n";