2.9.4 Unification (version 2)

See also section 2.12.

bool PlTerm::unify_term(PlTerm)

bool PlTerm::unify_atom(PlAtom)

bool PlTerm::unify_atom(string)

bool PlTerm::unify_list_codes(string)

bool PlTerm::unify_list_chars(string)

bool PlTerm::unify_integer(int)

bool PlTerm::unify_float(double)

bool PlTerm::unify_string(string)

bool PlTerm::unify_functor(PlFunctor)

bool PlTerm::unify_pointer(void *)

bool PlTerm::unify_nil()

bool PlTerm::unify_blob(void *blob, size_t len, PL_blob_t *type)

bool PlTerm::unify_chars(int flags, size_t len, const char *s)

A family of unification methods are defined for the various Prolog types and C++ types. Wherever string is shown, you can use:

• char*
• whar_t*
• std::string
• std::wstring

Here is an example:

PREDICATE(hostname, 1)
{ char buf[256];
  if ( gethostname(buf, sizeof buf) == 0 )
    return A1.unify_atom(buf);
  return false;
}

An alternative way of writing this would use the PlCheck() to raise an exception if the unification fails.

PREDICATE(hostname2, 1)
{ char buf[256];
  PlCheck(gethostname(buf, sizeof buf) == 0);
  PlCheck(A1.unify_atom(buf));
  return true;
}

Of course, in a real program, the failure of gethostname(buf)sizeof buf should create an error term than contains information from errno.