::/2

Description

Object::Predicate
{Proxy}::Predicate

Sends a message to an object. The message argument must match a public predicate of the receiver object. When the message corresponds to a protected or private predicate, the call is only valid if the sender matches the predicate scope container.

The {Proxy}::Predicate syntax construct allows simplified access to parametric object proxies. Its operational semantics is equivalent to the goal conjunction ({Proxy}, Proxy::Predicate). I.e. Proxy is proved as a plain Prolog goal and, if successful, the goal term is used as a parametric object identifier. Exceptions thrown when proving Proxy are handled by the ::/2 control construct. This syntax construct supports backtracking over the {Proxy} goal.

Template and modes

+object_identifier::+callable
{+object_identifier}::+callable

Errors

Either Object or Predicate is a variable:

instantiation_error

Object is not a valid object identifier:

type_error(object_identifier, Object)

Predicate is neither a variable nor a callable term:

type_error(callable, Predicate)

Predicate is declared private:

permission_error(access, private_predicate, Predicate)

Predicate is declared protected:

permission_error(access, protected_predicate, Predicate)

Predicate is not declared:

existence_error(predicate_declaration, Predicate)

Object does not exist:

existence_error(object, Object)

Proxy is a variable:

instantiation_error

Proxy is not a valid object identifier:

type_error(object_identifier, Proxy)

The predicate Proxy does not exist in the user pseudo-object:

existence_error(procedure, ProxyFunctor/ProxyArity)

Examples

| ?- list::member(X, [1, 2, 3]).

X = 1 ;
X = 2 ;
X = 3
yes