det/1

Documentation
- Reference manual
  - Built-in Predicates
    - Debugging and declaring determinism
      - det/1
      - $/0
      - $/1
- Packages

Availability:built-in

[directive]det(+PredicateIndicators)

Declare a number of predicates as det (deterministic). As a result, both failure and success with a choicepoint is considered an error. The behaviour if the declaration is violated is controlled with the Prolog flag determinism_error. The default is to raise an exception (error). Consider the following program:

:- det(p/1).

p(1).
p(2).

Now, a call ?- p(1). behaves normally. However:

?- p(X).
ERROR: Deterministic procedure p/1 succeeded with a choicepoint
ERROR: In:
ERROR:   [10] p(1)

?- p(a).
ERROR: Deterministic procedure p/1 failed
ERROR: In:
ERROR:   [10] p(a)

Violations throw an error/2 exception determinism_error(Pred, Declared, Observed, property).

The trap/1 (cli) or gtrap/1 (gui) predicate can be used to make the debugger stop near the error. For example:

?- gtrap(determinism_error(_,_,_,_)).