1:- module(
    2  counter,
    3  [
    4    counter_create/1,    % -Counter
    5    counter_increment/1, % +Counter
    6    counter_increment/2, % +Counter, -Value
    7    counter_value/2      % +Counter, ?Value
    8  ]
    9).

   15:- use_module(library(nb_ext)).

 counter_create(-Counter:compound) is det

   21counter_create(counter(0)).

 counter_increment(+Counter:compound) is det

 counter_increment(+Counter:compound, -Value:nonneg) is det

   28counter_increment(Counter) :-
   29  counter_increment(Counter, _).
   30
   31
   32counter_increment(Counter, Value) :-
   33  nb_increment(Counter, 1, Value).

 counter_value(+Counter:compound, +N:nonneg) is semidet

counter_value(+Counter:compound, -N:nonneg) is det

   40counter_value(counter(N), N)