>>matt_d+(OP)
Abstract. Logic programming has a long history. The representative of
logic programming in practice, the language Prolog, has been introduced
more than 50 years ago. The main features of Prolog are still present
today: a Prolog program is a set of predicate definitions executed by
resolution steps with a backtracking search strategy. The use of back-
tracking was justified by efficiency reasons when Prolog was invented.
However, its incompleteness destroys the elegant connection of logic pro-
gramming and the underlying Horn clause logic and causes difficulties to
teach logic programming. Moreover, the restriction to predicates hinders
an adequate modeling of real world problems, which are often functions
from input to output data, and leads to unnecessarily inefficient exe-
cutions. In this paper we show a way to overcome these problems. By
transforming predicates and goals into functions and nested expressions,
one can evaluate them with a demand-driven strategy which might re-
duce the number of computation steps and avoid infinite search spaces.
Replacing backtracking by complete search strategies with new imple-
mentation techniques closes the gap between the theory and practice of
logic programming. In this way, we can keep the ideas of logic program-
ming in future programming systems.