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clause(+Clause)
Succeeds if Clause unifies with a clause of a dynamic procedure.
- +Clause
- Atom or compound term
Description
Finds a dynamic clause whose head unifies with the head of Clause and
unifies the body of the clause with the body of Clause. The head of
Clause must be sufficiently instantiated so that the predicate (head) of
the clause can be determined. The functor of the head of Clause must be
that of a procedure previously declared as dynamic using dynamic/1.
This goal may be resatisfied if there are several clauses which match
the first argument. In the first solution the argument will be unified
with the first such clause. Subsequent solutions will unify the
argument to the other clauses in the same order in which they are listed
by listing/0, 1.
clause/1 satisfies the logical update semantics. When clause/1 is first
called, it makes a virtual copy of the clauses that match and, on
backtracking, unifies its argument with them. Any modifications made to
the procedure after clause/1 has started executing do not, in any way,
affect the solutions produced. A subsequent call, however makes and
uses a new, virtual, copy of the modified database.
Fail Conditions
Fails if no dynamic clause unifies with Clause
Resatisfiable
Yes
Exceptions
- (4) instantiation fault
- Clause is not instantiated
- (4) instantiation fault
- The head of Clause is a free variable.
- (63) procedure not dynamic
- Procedure is not dynamic
- (70) accessing an undefined dynamic procedure
- Procedure is undefined
See Also