Constraint-logic object-oriented programming is useful in the integrated development of business software that occasionally solves constraint-logic problems. So far, work in constraint-logic objectoriented programming was limited to considering constraints that only involve logic variables of primitive types; in particular, boolean, integer, and floating-point numbers. However, the availability of object-oriented features calls for the option to use logic variables in lieu of objects as well. Therefore, support for reference-type logic variables (or free objects) is required. With the present work, we add support for reference-type logic variables to a Java-based constraint-logic objectoriented language. Allowing free objects in statements and expressions results in novel interactions with objects at runtime, for instance, non-deterministic execution of invocations on free objects (taking arbitrary class hierarchies and overriding into account). In order to achieve this, we also propose a dynamic type constraint that restricts the types of free objects at runtime.

Working Paper Sketch ..... 3 1 Programming with Free Objects ..... 4 2 Constraint-logic Object-oriented Programming with Muli ..... 5 2.1 Setting the Stage for Free Objects ..... 7 3 Method Invocations on Free Objects ..... 11 4 Field Access on Free Objects ..... 13 5 Other Operations on Free Objects ..... 14 5.1 Type Operations ..... 14 5.2 Equality ..... 15 6 Demonstration ..... 16 7 Related Work ..... 18 8 Concluding Remarks ..... 19 A Operational Semantics of Muli (Excerpt) ..... 20 B Implementation of Board and Queens ..... 22 References ..... 23