C. Beierle and E. Börger. Specification and correctness proof of a WAM extension for type-constraint logic programming. Formal Aspects of Computing, 8(4):428-462, 1996.


We provide a mathematical specification of an extension of Warren's Abstract Machine for executing Prolog to type-constraint logic programming and prove its correctness. Our aim is to provide a full specification and correctness proof of a concrete system, the PROTOS Abstract Machine (PAM), an extension of the WAM by polymorphic order-sorted unification as required by the logic programming language PROTOS-L.

In the first part of the paper, we keep the notion of types and dynamic type constraints rather abstract to allow applications to different constraint formalisms like Prolog III or CLP(R). This generality permits us to introduce modular extensions of Börger's and Rosenzweig's formal derivation of the WAM. Since the type constraint handling is orthogonal to the compilation of predicates and clauses, we start from type-constraint Prolog algebras with compiled AND/OR structure that are derived from Börger's and Rosenzweig's corresponding compiled standard Prolog algebras. The specification of the type-constraint WAM extension is then given by a sequence of evolving algebras, each representing a refinement level, and for each refinement step a correctness proof is given. Thus, we obtain the theorem that for every such abstract type-constraint logic programming system L, every compiler to the WAM extension with an abstract notion of types which satisfies the specified conditions, is correct.

In the second part of the paper, we refine the type constraints to the polymorphic order-sorted types of PROTOS-L. This allows us to develop a detailed, yet due to the use of evolving algebras, mathematically precise account of the PAM's compiled type constraint representation and solving facilities, and to extend the correctness theorem to compilation on the fully specified PAM.

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