Program transformation

About: Program transformation is a research topic. Over the lifetime, 2468 publications have been published within this topic receiving 73415 citations.

Epistemic Foundation of the Well-Founded Semantics over Bilattices

Abstract: We define new, both model-theoretical and fixpoint-based, characterizations of the well-founded semantics for logic programs in the general setting of bilattices. This work lights the role of the CWA, used in the well-founded semantics as a carrier of falsehood, and shows that the definition of that semantics does not require any separation of positive and negative information nor any program transformation.

A path-sensitively sliced control flow graph

Abstract: We present a new graph representation of programs with specified target variables. These programs are intended to be processed by third-party applications querying target variables such as testers and verifiers. The representation embodies two concepts. First, it is path-sensitive in the sense that multiple nodes representing one program point may exist so that infeasible paths can be excluded. Second, and more importantly, it is sliced with respect to the target variables. This key step is founded on a novel idea introduced in this paper, called ``Tree Slicing'', and on the fact that slicing is more effective when there is path sensitivity. Compared to the traditional Control Flow Graph (CFG), the new graph may be bigger (due to path-sensitivity) or smaller (due to slicing). We show that it is not much bigger in practice, if at all. The main result however concerns its quality: third-party testers and verifiers perform substantially better on the new graph compared to the original CFG.

Logic + control: On program construction and verification

Abstract: This paper presents an example of formal reasoning about the semantics of a Prolog program of practical importance (the SAT solver of Howe and King). The program is treated as a definite clause logic program with added control. The logic program is constructed by means of stepwise refinement, hand in hand with its correctness and completeness proofs. The proofs are declarative – they do not refer to any operational semantics. Each step of the logic program construction follows a systematic approach to constructing programs which are provably correct and complete. We also prove that correctness and completeness of the logic program is preserved in the final Prolog program. Additionally, we prove termination, occur-check freedom and non-floundering. Our example shows how dealing with “logic” and with “control” can be separated. Most of the proofs can be done at the “logic” level, abstracting from any operational semantics. The example employs approximate specifications; they are crucial in simplifying reasoning about logic programs. It also shows that the paradigm of semantics-preserving program transformations may be not sufficient. We suggest considering transformations which preserve correctness and completeness with respect to an approximate specification.

Compiling Lisp programs for parallel execution

Abstract: Curare, the program restructurer described in this paper automatically transforms a sequential Lisp program into an equivalent concurrent program that runs on a multiprocessor.