Sync

Task/Exceptions/Logtalk/exceptions-1.logtalk

@@ -0,0 +1,23 @@
+:- object(exceptions).
+
+    :- public(double/2).
+    double(X, Y) :-
+        catch(double_it(X,Y), Error, handler(Error, Y)).
+
+    handler(error(not_a_number(X), logtalk(This::double(X,Y), Sender)), Y) :-
+        % try to fix the error and resume computation;
+        % if not possible, rethrow the exception
+        (   catch(number_codes(Nx, X), _, fail) ->
+            double_it(Nx, Y)
+        ;   throw(error(not_a_number(X), logtalk(This::double(X,Y), Sender)))
+        ).
+
+    double_it(X, Y) :-
+        (   number(X) ->
+            Y is 2*X
+        ;   this(This),
+            sender(Sender),
+            throw(error(not_a_number(X), logtalk(This::double(X,Y), Sender)))
+        ).
+
+:- end_object.

Task/Exceptions/Logtalk/exceptions-2.logtalk

@@ -0,0 +1,10 @@
+| ?- exceptions::double(1, Double).
+Double = 2
+yes
+
+| ?- exceptions::double("1", Double).
+Double = 2
+yes
+
+| ?- exceptions::double(a, Double).
+uncaught exception: error(not_a_number(a),logtalk(exceptions::double(a,_),user))