6.8 Operators and modules

Operators (section 4.25) are local to modules, where the initial table behaves as if it is copied from the module user (see section 6.10). A specific operator can be disabled inside a module using :- op(0, Type, Name). Inheritance from the public table can be restored using :- op(-1, Type, Name).

In addition to using the op/3 directive, operators can be declared in the module/2 directive as shown below. Such operator declarations are visible inside the module, and importing such a module makes the operators visible in the target module. Exporting operators is typically used by modules that implement sub-languages such as chr (see chapter 8). The example below is copied from the library library(clpfd).

:- module(clpfd,
          [ op(760, yfx, #<==>),
            op(750, xfy, #==>),
            op(750, yfx, #<==),
            op(740, yfx, #\/),
            ...
            (#<==>)/2,
            (#==>)/2,
            (#<==)/2,
            (#\/)/2,
            ...
          ]).