Oz Explorer: A Visual Constraint Programming Tool

This paper describes the Oz Explorer and its implementation. The Explorer is a visual constraint programming tool intended to support the development of constraint programs. It uses the search tree of a constraint problem as its central metaphor. Exploration and visualization of the search tree are user-driven and interactive. The constraints of any node in the tree are available first-class: predefined or user-defined procedures can be used to display or analyze them. The Explorer is a fast and memory efficient tool intended for the development of real-world constraint programs. The Explorer is implemented in Oz using first-class computation spaces. There is no fixed search strategy in Oz. Instead, first-class computation spaces allow to program search engines. The Explorer is one particular example of a user-guided search engine. The use of recomputation to trade space for time makes it possible to solve large real-world problems, which would use too much memory otherwise.