Equivalences and transformations of regular systems—Applications to recursive program schemes and grammars☆

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 introduces Composable Attribute Grammars (CAGs), a formalism that extends classical attribute grammars to allow for the modular composition of translation specifications and of translators. CAGs bring to complex translator writing systems the same benefits of modularity found in modern programming languages, including comprehensibility, reusability, and incremental meta-compilation.A CAG is built from several smaller component AGs, each of which solves a particular subproblem, such as name analysis or register allocation. A component AG is based upon a simplified phrase-structure that reflects the properties of its subproblem rather than the phrase-structure of the source language. Different component phrase-structures for various subproblems are combined by mapping them into a phrase-structure for the source language. Both input and output attributes can be associated with the terminal symbols of a component AG. Output attributes enable the results of solving a subproblem to be distributed back to anywhere that originally contributed part of the subproblem, e.g. transparently distributing the results of global name analysis back to every symbolic reference in the source program.After introducing CAGs by way of an example, we provide a formal definition of CAGs and their semantics. We describe a subclass of CAGs and their semantics. We describe a subclass of CAGs, called separable CAGs, that have favorable implementation properties. We discuss the novel aspects of CAGs, compare them to other proposals for inserting modularity into attribute grammars, and relate our experience using CAGs in the Linguist translator-writing system.

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Composable attribute grammars: support for modularity in translator design and implementation

https://hal.inria.fr/inria-00075310/document

Proof methods of declarative properties of definite programs

An extension of the inductive assertion method allowing one to prove the partial correctness of an attribute grammar w.r.t. a specification is presented. It is complete in an abstract sense. It is also shown that the semantics of systems of recursive imperative procedures or of recursive applicative procedures computed with call-by-value or call-by-name can be expressed by an attribute grammar associating attributes with the nodes of the so-called trees of calls. Hence the proof methods for the partial correctness of attribute grammars can be applied to these recursive procedures. We show also how the proof method can be applied in logic programming.

B. Courcelle

Papers

Attribute grammars : definitions, analysis of dependencies, proof methods