/*
 *  call-seq:
 *     class.superclass -> a_super_class or nil
 *  
 *  Returns the superclass of <i>class</i>, or <code>nil</code>.
 *     
 *     File.superclass     #=> IO
 *     IO.superclass       #=> Object
 *     Object.superclass   #=> nil
 *     
 */

static VALUE
rb_class_superclass(klass)
    VALUE klass;
{
    VALUE super = RCLASS(klass)->super;

    if (!super) {
        rb_raise(rb_eTypeError, "uninitialized class");
    }
    if (FL_TEST(klass, FL_SINGLETON)) {
        super = RBASIC(klass)->klass;
    }
    while (TYPE(super) == T_ICLASS) {
        super = RCLASS(super)->super;
    }
    if (!super) {
        return Qnil;
    }
    return super;
}