In logic programming or functional programming languages, data objects, such as terms and lists, are immutable. In a basic implementation of such language, updating one element of an aggregate (contiguous data structure, such as an array) involves making a new copy of the whole aggregate. However, such copying can be expensive, and can be avoided by using a destructive update. We introduce the concept of a wrapper which enables destructive operation on an immutable object. Based on this concept, we designed the reversible functor as a solution to the aggregate update problem. We implemented the reversible functor in the existing SB-Prolog system and carried out several benchmarks. These benchmark results show its effectiveness. When using a large functor and updating it many times, the performance is improved dramatically by implementing the reversible functor. It incurs some overhead at runtime, but the amount is small and acceptable.

This paper proposes a new environment for high-level VLSI design specification validation using "Algorithmic Debugging" and evaluates its benefits on three significant examples (a protocol processor, an 8-bit CPU, and a Prolog processor). A design is specified at a high-level using the structured analysis (SA) method, which is useful for analyzing and understanding the functionality to be realized. The specification written in SA is transformed into a logic programming language and is simulated in it. The errors (which terminate with an incorrect output in the simulation) included in the three large examples are efficiently located by answering junt a few queries from the algorithmic debugger. The number of interactions between the designer and the debugger is reduced by a factor of ten to a hundred compared to conventional simulation based validation methodologies. The correct SA specification can be automatically translated into a Register Transfer Level (RTL) specification suitable for logic synthesis. In this environment, a designer is freed from the tedious task of debugging a RTL specification, and can concentrate on the design itself. This environment promises to be an important step towards efficient high-level VLSI design specification validation.