3.1 Hello(World)

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 " << (char *)A1 << 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. Casting a PlTerm to a char * or wchar_t * provides the natural 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