AVOIDING TWO-LEVEL SYSTEMS: USING A TEXTUAL ENVIRONMENT TO ADDRESS CROSS-CUTTING CONCERNS

We believe that, owing to the paucity of textual facilities in contemporary HLLs (high-level languages), large software systems frequently require an additional level of meta-programming to sufficiently address their cross-cutting concerns. A programming team can either implement its system by both writing the main application in a slightly customised language and the corresponding customised compiler for it, or it can use a macro pre-processor to provide the remaining cross-cutting requirements not found in the chosen HLL. With either method, a two-level system arises. This paper argues that textual macro-programming is an important cross-cutting medium, that existing proposals for sets of pre-defined AOP (aspect-oriented programming) joinpoints are overly constrictive and that a generalised meta-programming facility, based on a textual environment should instead be directly embedded in HLLs. The paper presents the semantics of the main additions required in an HLL designed with this feature. We recommend that the textual features must be compiled out as the reference semantics would generally be too inefficient if naively interpreted.