EqL: The Language and Its Implementation

EqL is a general-purpose language that combines the capabilities of functional and logic programming languages. A program in EqL consists of a collection of conditional, pattern-directed rules, where the conditions are expressed as a conjunction of equations, and the patterns are terms built up of data-constructors and basic values. The computational paradigm in EqL is equation solving. In this paper we describe EqL informally, and present examples illustrating the major features of the language: nondeterminism, deferred evaluation of primitives, and logical variables. This paper also describes the novel aspects of a sequential implementation for EqL: compile-time flattening of equations; and run-time equation-delaying and last-equation optimization.