control construct




Sends a message to self. Can only used in the body of a predicate definition. The argument should match a public or protected predicate of self. It may also match a private predicate if the predicate is within the scope of the object where the method making the call is defined, if imported from a category, if used from within a category, or when using private inheritance. When the predicate is declared but not defined, the message simply fails (as per the closed-world assumption).

The lookups for the message declaration and the corresponding method are performed using a depth-first strategy. A message to self necessarily implies the use of dynamic binding but a caching mechanism is used to improve performance in subsequent messages. See the User Manual section on performance for details.

Modes and number of proofs

::+callable - zero_or_more


Message is a variable:
Message is neither a variable nor a callable term:
type_error(callable, Message)
Message, with predicate indicator Name/Arity, is declared private:
permission_error(access, private_predicate, Name/Arity)
Message, with predicate indicator Name/Arity, is not declared:
existence_error(predicate_declaration, Name/Arity)


area(Area) :-
    Area is Width * Height.

See also

(::)/2, (^^)/1, []/1