Execution levels for aspect-oriented programming

Abstract

In aspect-oriented programming languages, advice evaluation is usually considered as part of the base program evaluation. This is also the case for certain pointcuts, such as if pointcuts in AspectJ, or simply all pointcuts in higher-order aspect languages like AspectScheme. While viewing aspects as part of base level computation clearly distinguishes AOP from reflection, it also comes at a price: because aspects observe base level computation, evaluating pointcuts and advice at the base level can trigger infinite regression. To avoid these pitfalls, aspect languages propose adhoc mechanisms, which increase the complexity for programmers while being insufficient in many cases. After shedding light on the many facets of the issue, this paper proposes to clarify the situation by introducing levels of execution in the programming language, thereby allowing aspects to observe and run at specific, possibly different, levels. We adopt a defensive default that avoids infinite regression in all cases, and give advanced programmers the means to override this default using level shifting operators. We implement our proposal as an extension of AspectScheme, and formalize its semantics. This work recognizes that different aspects differ in their intended nature, and shows that structuring execution contexts helps tame the power of aspects and metaprogramming.

A Comparison of Implementations for Aspect-Oriented JavaScript

“…It also takes full advantages of the higherorder programming to make the definitions for pointcuts and aspects more precision. And integrates scoping strategies [10,11,12], it provides proper control over the scope of dynamically-deployed aspects. The way that adopts the hybrid join point model makes it possible to extend the framework richly.…”

Effective Aspects: A Typed Monadic Embedding of Pointcuts and Advice

“…when an aspect execution produces join points that are visible to others, including itself [41]. Execution levels give structure to execution by establishing a tower in which the flow of control navigates.…”

“…In addition to level shifting with up and down, current reifies the current level, and lambda_at creates a level-capturing function bound at level l . When such a function is applied, execution jumps to level l and then goes back to the level prior to the application [41].…”

“…The above extensions can be implemented in an dynamically typed language such as LAScheme [41]. However, it is challenging to provide any kind of reasoning about effects due to the dynamic nature of the language.…”

“…He illustrated the extensibility approach with execution levels [41] and level-aware exception handling [13]. The authors then worked on a practical monadic aspect weaver in Typed Racket [14].…”