The exponential storage cost of d-schemes

Structured programming has been studied recently in the context of program schemes. It is in this setting that we wish to examine the question of the "inefficiency'; of structured programs. In particular, we study the "intrinsic size'; of structured program schemes when compared to equivalent nonstructured schemes. The notion of equivalence used is the one requiring equivalent schemes to compute the same function for each interpretation of their common operator and predicate symbols. To study the "intrinsic size'; of a structured scheme, we examine the size of a smallest equivalent structured scheme, and compare this with the size of a smallest equivalent nonstructured scheme. The general class of schemes studied in the present paper is the class of Ianov schemes, and the "structured'; schemes considered are the so-called Dijkstra schemes. The primary result is, from some points of view, a negative one: the intrinsic size of Dijkstra schemes may be exorbitant. To be precise, we construct a sequence F_{n} of Dijkstra schemes such that for each n, no smaller Dijkstra scheme is equivalent to F_{n}, and the number of edges in F_{n} grows exponentially. We then show there are weak equivalent nonstructured schemes G_{n} whose size grows only linearly

SLR inference: An inference system for fixed-mode logic programs, based on SLR parsing

AbstractDefinite-clause grammars (DCGs) generalize context-free grammars in such a way that Prolog can be used as a parser in the presence of context-sensitive information. Prolog's proof procedure, however, is based on backtracking, which may be a source of inefficiency. Parsers for context-free grammars that use backtracking, for instance, were soon replaced by more efficient methods, such as LR parsers. This suggests incorporating the principles underlying LR parsing into a parser for grammars with context-sensitive information. We present a technique that applies a transformation to the program/grammar by adding leaves to the proof/parse trees and placing the contextual information in such leaves. An inference system is then easily obtained from an LR parser, since only the parts dealing with terminals (which appear at the leaves) must be modified. Although our method is restricted to programs with fixed modes, it may be preferable to DCGs under Prolog for some programs

A survey of models for parallel computing

Survey of models for parallel computin