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.. rst-class:: align-right

built-in method

.. index:: pair: asserta/1; Built-in method .. _methods_asserta_1:

asserta/1

Description

::

asserta(Head) asserta((Head:-Body))

Asserts a clause as the first one for an object dynamic predicate.

When the predicate was not previously declared (using a scope directive), a dynamic predicate declaration is added to the object. In this case, the predicate scope depends on how this method is called:

asserta(Clause) The predicate is dynamically declared as :term:`private <private predicate>`. ::asserta(Clause) The predicate is dynamically declared as :term:`protected <protected predicate>`. Object::asserta(Clause) The predicate is dynamically declared as :term:`public <public predicate>`.

Note, however, that dynamically declaring a new predicate requires either a local assert or the :ref:`dynamic_declarations <flag_dynamic_declarations>` compiler flag set to allow when the object was created or compiled.

When the predicate indicator for Head is declared in a :ref:directives_uses_2 or :ref:directives_use_module_2 directive, the clause is asserted in the referenced object or module. When the backend Prolog compiler supports a module system, the predicate argument can also be module qualified.

This method may be used to assert clauses for predicates that are not declared dynamic for dynamic objects provided that the predicates are declared in :term:this. This allows easy initialization of dynamically created objects when writing constructors.

Modes and number of proofs

::

asserta(+clause) - one

Errors

| Head is a variable: | instantiation_error | Head is a neither a variable nor a callable term: | type_error(callable, Head) | Body cannot be converted to a goal: | type_error(callable, Body) | The predicate indicator of Head, Name/Arity, is that of a private predicate: | permission_error(modify, private_predicate, Name/Arity) | The predicate indicator of Head, Name/Arity, is that of a protected predicate: | permission_error(modify, protected_predicate, Name/Arity) | The predicate indicator of Head, Name/Arity, is that of a static predicate: | permission_error(modify, static_predicate, Name/Arity) | The predicate indicator of Head, Name/Arity, does not match a declared predicate and the target object was created or compiled with support for dynamic declaration of predicates turned off: | permission_error(create, predicate_declaration, Name/Arity)

Examples

| To assert a clause as the first one for a local dynamic predicate or a dynamic predicate in :term:this: | asserta(Clause) | To assert a clause as the first one for any public or protected dynamic predicate in :term:self: | ::asserta(Clause) | To assert a clause as the first one for any public dynamic predicate in an explicit object: | Object::asserta(Clause)

An example of asserting clauses in :term:this and in :term:self from a category:

::

:- category(attributes, implements(attributes_protocol)).

:- private(attr_/1). :- dynamic(attr_/1).

set_in_this(A, X) :- asserta(attr_(A, X)).

set_in_self(A, X) :- ::asserta(attr_(A, X)).

...

An example of asserting clauses into another object with the predicates listed using a :ref:directives_uses_2 directive (similar when using a :ref:directives_use_module_2 directive):

::

:- object(reasoner(_KnowledgeBase_)).

:- uses(_KnowledgeBase_, [
    foo/1, bar/1
]).

baz(X) :-
   % compiled as _KnowledgeBase_::assertz(foo(X))
   asserta(foo(X)).

foobar(Name, Argument) :- Clause =.. [Name, Argument], % runtime resolved to KnowledgeBase::assertz(Clause) % when Name is either foo or bar asserta(Clause).

...

.. seealso::

:ref:methods_abolish_1, :ref:methods_assertz_1, :ref:methods_clause_2, :ref:methods_retract_1, :ref:methods_retractall_1 :ref:directives_dynamic_0, :ref:directives_dynamic_1, :ref:directives_uses_2, :ref:directives_use_module_2