range.c:438
static VALUE
range_include(range, val)
    VALUE range, val;
{
    VALUE beg, end;

    beg = rb_ivar_get(range, id_beg);
    end = rb_ivar_get(range, id_end);
    if (r_le(beg, val)) {
	if (EXCL(range)) {
	    if (r_lt(val, end)) return Qtrue;
	}
	else {
	    if (r_le(val, end)) return Qtrue;
	}
    }
    return Qfalse;
}
