This simple example shows the basic definition of the predicate hello/1 and how a Prolog argument is converted to C-data:
PREDICATE(hello, 1)
{ cout << "Hello " << A1.as_string() << endl;
return true;
}
The arguments to PREDICATE() are the name and arity of the
predicate. The macros A<n> provide access to the
predicate arguments by position and are of the type PlTerm.
The C or C++ string for a PlTerm can be extracted using as_string(),
or as_wstring() methods;11The
C-string values can be extracted from std::string by using c_str(),
but you must be careful to not return a pointer to a local/stack value.
and similar access methods provide an easy type-conversion for most
Prolog data-types, using the output of write/1
otherwise:
?- hello(world). Hello world Yes ?- hello(X) Hello _G170 X = _G170