A Conservative Approach toMeta - Programming in Constraint

Constraint Logic Programming 4] extends Logic Programming by generalizing the notion of uniication to constraint solving. This is achieved by xing the interpretation of some of the symbols in the language. The two alternative mechanisms used in the currently implemented CLP systems to achieve this operation are: (1) x the interpretation before the program executes or (2) x the interpretation at a point during program execution when it is used in a constraint. CLP(R) 5] and Prolog-III 1] take the rst approach whereas CHIP 2] takes the second approach. The problem with the rst approach is that interpreted terms cannot be manipulated syntactically. The problem with the second approach is that all constraint operations have to be made explicit and this increases the diiculty of programming. We propose a synthesis of both approaches that overcomes their individual diiculties. Our method is implemented in the ECL i PS e compiler system.