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Predicate dynamic/1
Availability:built-in
Source[ISO]dynamic :PredicateIndicator, ...
Informs the interpreter that the definition of the predicate(s) may change during execution (using assert/1 and/or retract/1). In the multithreaded version, the clauses of dynamic predicates are shared between the threads. The directive thread_local/1 provides an alternative where each thread has its own clause list for the predicate. Dynamic predicates can be turned into static ones using compile_predicates/1.

Examples

Dealing with dynamic predicatesJan Wielemaker

Dealing with dynamic predicates

A dynamic predicate is introduced using dynamic/1, after which clauses may be added using assertz/1. Persistent dynamic predicates are realized using library(persistency).

:- dynamic p/1.
?- assertz(p(a)).
?- p(X).
X = a.
?- retractall(p(_)).
?- p(X).
false.
author
- Jan Wielemaker
retractall/1 or abolish/1?

retractall/1 or abolish/1?

The retractall/1 predicate removes all clauses whose head matches the argument from a dynamic predicate. The abolish/1 predicate takes a predicate indicator to remove all clauses and all properties.

:- dynamic p/1.

?- assertz(p(a)).
?- assertz(p(b)).
?- retractall(p(b)).
?- p(a).
true.
?- p(b).
false.
?- retractall(p(_)).
?- p(X).
false.
?- assertz(p(a)).
?- assertz(p(b)).
?- abolish(p/1).
?- p(X).
ERROR: Unknown procedure: p/1 (DWIM could not correct goal)
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LogicalCaptain said (2020-05-22T12:02:35):0 upvotes 0 0 downvotes
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See also:

Database Section which has more on this.

Predicates that are unknown are implicitly defined as dynamic when they appear first-time in: asserta/1, asserta/2, assertz/1, assertz/2, retract/2, retractall/1

Examples:

Use predicate like a dynamic predicate, but the predicate was previously used non-dynamically: NO

?- [user].
|: tryit_0(a,b).
|: % user://1 compiled 0.02 sec, 1 clauses
true.

?- assertz(tryit_0(c,d)).
ERROR: No permission to modify static procedure `tryit_0/2'

Declared as dynamic before use: YES

?- [user].
|: :- dynamic(tryit_1/2).
|: tryit_1(a,b).
|: % user://1 compiled 0.02 sec, 1 clauses
true.

?- assertz(tryit_1(c,d)).
true.

?- bagof([X,Y],tryit_1(X,Y),Bag).
Bag = [[a, b], [c, d]].

In SWI Prolog, dynamic/1 also appears as a predicate

?- dynamic(tryit_2/2).
true.

?- assertz(tryit_2(a,b)).
true.

?- bagof([X,Y],tryit_2(X,Y),Bag).
Bag = [[a, b]].

Use a previously unknown predicate dynamically: Implicitly dynamic

?- assertz(tryit_3(a,b)).
true.

?- predicate_property(tryit_3(_,_),dynamic).
true.

Edge case: Testing for dynamic property before use

?- predicate_property(tryit_5(_,_),dynamic).   % Should properly throw, really
false.

?- assertz(tryit_5(a,b)).
true.

?- predicate_property(tryit_5(_,_),dynamic).
true.