Semantics and scoping of aspects in higher-order languages

Aspect-oriented software design will need to support languages with first-class and higher-order procedures, such as Ruby, Perl, ML and Scheme. These language features present both challenges and benefits for aspects. On the one hand, they force the designer to carefully address issues of scope that do not arise in first-order languages. On the other hand, these distinctions of scope make it possible to define a much richer variety of policies than first-order aspect languages permit. In this paper, we describe the subtleties of pointcuts and advice for higher-order languages, particularly Scheme. We then resolve these subtleties by alluding to traditional notions of scope. In particular, programmers can now define both dynamic aspects traditional to aop and static aspects that can capture common security-control paradigms. We provide an operational semantics, based on an extended ceks machine, that gives a formal account of dynamic and static aspects. We implement the language as an extension to Scheme. By exploiting two novel features of our Scheme system—continuation marks and language-defining macros—the implementation is lightweight and integrates well into the programmer’s toolkit.