CHANGED: Rewrite of the counter module API.

Changes in module `counter`:

- Renamed `create_counter/1` to `counter_create/1`.
- Renamed `increment_counter/1` to `counter_increment/1`.
- Added `counter_increment/2`.
- Reimplemented by using module `nb_ext`.

Additions to module `nb_ext`:

- Added `nb_increment/3`.
- Added `nb_plus/4`.

prolog/counter.pl

@@ -1,36 +1,40 @@
 :- module(
   counter,
   [
-    counter_value/2,    % +Counter, ?N
-    create_counter/1,   % -Counter
-    increment_counter/1 % +Counter
+    counter_create/1,    % -Counter
+    counter_increment/1, % +Counter
+    counter_increment/2, % +Counter, -Value
+    counter_value/2      % +Counter, ?Value
   ]
 ).
 
 /** <module> A simple counter
 
 */
 
+:- use_module(library(nb_ext)).
 
 
 
+%! counter_create(-Counter:compound) is det.
 
-%! counter_value(+Counter:compound, +N:nonneg) is semidet.
-%! counter_value(+Counter:compound, -N:nonneg) is det.
+counter_create(counter(0)).
 
-counter_value(counter(N), N).
 
 
+%! counter_increment(+Counter:compound) is det.
+%! counter_increment(+Counter:compound, -Value:nonneg) is det.
 
-%! create_counter(-Counter:compound) is det.
+counter_increment(Counter) :-
+  counter_increment(Counter, _).
 
-create_counter(counter(0)).
 
+counter_increment(Counter, Value) :-
+  nb_increment(Counter, 1, Value).
 
 
-%! increment_counter(+Counter:compound) is det.
 
-increment_counter(Counter) :-
-  arg(1, Counter, N1),
-  N2 is N1 + 1,
-  nb_setarg(1, Counter, N2).
+%! counter_value(+Counter:compound, +N:nonneg) is semidet.
+%! counter_value(+Counter:compound, -N:nonneg) is det.
+
+counter_value(counter(N), N).

prolog/nb_ext.pl

@@ -2,7 +2,9 @@
   nb_ext,
   [
     nb_increment/2, % +State, +Index
-    nb_plus/3       % +State, +Index, +Value
+    nb_increment/3, % +State, +Index, -Value
+    nb_plus/3,      % +State, +Index, +Increment
+    nb_plus/4       % +State, +Index, +Increment, -Value
   ]
 ).
 
@@ -12,20 +14,35 @@
 
 */
 
-
+:- use_module(library(clpfd)).
 
 
 
 %! nb_increment(+State:compound, +Index:positive_integer) is det.
 
 nb_increment(State, Index) :-
-  nb_plus(State, Index, 1).
+  nb_increment(State, Index, _).
+
+
+%! nb_increment(+State:compound, +Index:positive_integer, -Value:nonneg) is det.
+
+nb_increment(State, Index, Value) :-
+  nb_plus(State, Index, 1, Value).
+
+
+
+%! nb_plus(+State:compound, +Index:positive_integer, +Increment:number) is det.
 
+nb_plus(State, Index, Increment) :-
+  nb_plus(State, Index, Increment, _).
 
 
-%! nb_plus(+State:compound, +Index:positive_integer, +Value:number) is det.
+%! nb_plus(+State:compound,
+%!         +Index:positive_integer,
+%!         +Increment:number,
+%!         -Value:nonneg) is det.
 
-nb_plus(State, Index, Value) :-
+nb_plus(State, Index, Increment, Value1) :-
   arg(Index, State, Value1),
-  Value2 is Value1 + Value,
+  Value2 #= Value1 + Increment,
   nb_setarg(Index, State, Value2).