Declarative language extensions for Prolog courses

In this paper we present several extensions to support a more declarative view of programming in Prolog. These extensions enable introductory Prolog courses to concentrate on the pure parts of Prolog for longer periods than without. Even quite complex programs can now be written free of any reference to the more problematic constructs. Our extensions include an alternate way to handle the occurs-check, efficient side-effect free I/O with DCGs, and a uniform approach to integer arithmetic that overcomes the disadvantages of arithmetical evaluation and finite domain constraints, but combines and amplifies their strengths. All extensions have been included recently into the SWI-Prolog distribution.