Options

\dlpindex{options} It is possible to declare how many solutions may be produced by setting the option sol as in .ds nat7.pl that will, when evaluating number, only produce the first seven natural numbers, including zero. It is important to note that backtracking occurs on the resumption goal Q? and not over the statement creating the process for evaluating a goal. For example the declaration .ds a.pl will effect that the goal
  :- Q = a!g(X), (X=3; X=2), Q?.
  
fails, whereas the goal
  :- Q = a!g(X), Q?, (X=3; X=2).
  
succeeds, since the binding X=3 in the first goal cannot be reached due to the fact that a produces only the solutions g(1) and g(2).