9.1 Variations of the PREDICATE macro

The PREDICATE() macros has a number of variations that deal with special cases.

PREDICATE0(name)

This is the same as PREDICATE(name, 0). It avoids a compiler warning about that PL_av is not used.

NAMED_PREDICATE(plname, cname, arity)

This version can be used to create predicates whose name is not a valid C++ identifier. Here is a ---hypothetical--- example, which unifies the second argument with a stringified version of the first. The `cname' is used to create a name for the functions. The concrete name does not matter, but must be unique. Typically it is a descriptive name using the limitations imposed by C++ indentifiers.

    NAMED_PREDICATE("#", hash, 2)
    { A2 = (wchar_t*)A1;
    }
    

NAMED_PREDICATE_NONDET(plname, cname, arity)

Define a non-deterministic Prolog predicate in C++. See SWI-cpp.h. FIXME: Needs cleanup and an example.