With attribute coupled grammars, descriptions of subsequent compilation phases can be composed to a single phase on the description level. This creates the opportunity for independent compiler modularization on the description versus the implementation level. The composition introduces a nontrivial reshaping of attribute dependencies, and hence affects the overall strategy for attribute evaluation. For a hierarchy of evaluation classes reaching from S-attributed to noncircular attribute couplings (ACs), we investigate whether they are closed under composition. Where closure does not hold, we identify subclasses which have the closure property. We show that closure of 1-ordered and simpler classes can only be achieved when there is only a single syntactic attribute allowed, while in the case of absolutely noncircular attribute couplings, an arbitrary number of synthesized syntactic attributes can be used. We show how (suboptimal) evaluators for the composed description are obtained directly from the evaluators of the separate phases. We also investigate the complementary problem of reducing the attribute evaluation complexity of a given, monolithic phase specification by finding an appropriate decomposition into subphases which all belong to simpler evaluation classes. In particular, we find that the closed subclass of sweep-evaluable ACs is generated by a proper subclass ofL-attributed ACs, while a similar characterization of 1-ordered ACs is proved to be impossible. Finally, we relate our observations to known results about descriptive power of attribute grammars and tree transducers.

Composition and evaluation of attribute coupled grammars

This paper surveys the main evaluation strategies for non-circular attribute grammars, i.e., passes, sweeps, visits and plans. Attention is also focused on the iteration of evaluation passes for circular attribute grammars.

Attribute Evaluation Methods

The problem of attribute evaluation during LR parsing is considered. Several definitions of LR-attributed grammars are presented. Relations of corresponding attribute grammar classes are analysed. Also the relations between LR-attributed grammars and LL-attributed grammars and between LR-attributed grammars and a class of one-pass attributed grammars based on left-corner grammars are considered.

The hierarchy of LR-Attributed Grammars

Attributed tree grammars

This paper deals with a method how an effective attribute-directed top-down parser and attribute evaluator can be constructed from a conditional L-attributed grammar (CLAG). The method is based on exploitation of an attribute stack in attribute evaluation and on definition of a translation scheme for CLAG.

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G. Filè

Papers

Theory of Attribute Grammars