. For object-oriented programming, the Visitor pattern enables the definition of a new operation on an object structure without changing the classes of the objects. The price has been that the set of classes must be fixed in advance, and they must each have a so-called accept method. In this paper we demonstrate how to program visitors without relying on accept methods and without knowing all classes of the objects in advance. The idea, derived from related work on shape polymorphism in functional programming, is to separate (1) accessing subobjects, and (2) acting on them. In the object-oriented setting, reflection techniques support access to sub-objects, as demonstrated in our Java class, Walkabout. It supports all visitors as subclasses, and they can be programmed without any further use of reflection. Thus a program using the Visitor pattern can now be understood as a specialized version of a program using the Walkabout class. 1 Introduction Design patterns [3] aim to make object...

AbstractResource-constrained devices are becoming ubiquitous. Examples include cell phones, palm pilots, and digital ther-mostats. It can be difficult to fit required functionality into such a device without sacrificing the simplicity and clarityof the software. Increasingly complex embedded systems require extensive brute-force testing, making development andmaintenance costly. This is particularly true for system components that are written in assembly language. Static check-ing has the potential of alleviating these problems, but until now there has been little tool support for programming at theassembly level.