Playing with TOY: Constraints and Domain Cooperation

This paper describes T OY, an implementation of a Constraint Functional Logic Programming scheme CFLP (C), where C is a coordination domain involving the cooperation among several constraint domains D1, ..., Dn via a mediatorial domain M . This implementation follows a cooperative goal solving calculus for CFLP (C) based on lazy narrowing, invocation of solvers for each domain Di, and projection operations for converting Di constraints into Dj constraints with the aid of mediatorial constraints supplied by M . Mediatorial constraints allow solving programs that require constraints of different domains, and projection may improve performance, allowing certain solvers to profit from (the projected forms) of constraints originally intended for other solvers. As a relevant concrete instance of our CFLP (C), we implemented the cooperation among Herbrand, real arithmetic and finite domain constraints, and the mediatorial constraints relate numeric variables belonging to the last two domains. These mediatorial constraints are the bridge #== :: int -> real -> bool (that evaluates to true if their arguments are equivalent -i.e., the real value is considered to represent the integer oneand false otherwise), and the antibridge #/== :: int -> real -> bool (with a countermeaning).