add push/pop to optimization context for convenience

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/api/api_opt.cpp

@@ -102,6 +102,23 @@ extern "C" {
         Z3_CATCH_RETURN(0);
     }
 
+    void Z3_API Z3_optimize_push(Z3_context c,Z3_optimize d) {
+        Z3_TRY;
+        LOG_Z3_optimize_push(c, d);
+        RESET_ERROR_CODE();
+        to_optimize_ptr(d)->push();
+        Z3_CATCH;
+    }
+
+    void Z3_API Z3_optimize_pop(Z3_context c,Z3_optimize d) {
+        Z3_TRY;
+        LOG_Z3_optimize_pop(c, d);
+        RESET_ERROR_CODE();
+        to_optimize_ptr(d)->pop(1);
+        Z3_CATCH;
+    }
+
+
     Z3_lbool Z3_API Z3_optimize_check(Z3_context c, Z3_optimize o) {
         Z3_TRY;
         LOG_Z3_optimize_check(c, o);

src/api/c++/z3++.h

@@ -1511,6 +1511,12 @@ namespace z3 {
         handle minimize(expr const& e) {
             return handle(Z3_optimize_minimize(ctx(), m_opt, e));
         }
+        void push() {
+            Z3_optimize_push(ctx(), m_opt);
+        }
+        void pop() {
+            Z3_optimize_pop(ctx(), m_opt);
+        }
         check_result check() { Z3_lbool r = Z3_optimize_check(ctx(), m_opt); check_error(); return to_check_result(r); }
         model get_model() const { Z3_model m = Z3_optimize_get_model(ctx(), m_opt); check_error(); return model(ctx(), m); }
         void set(params const & p) { Z3_optimize_set_params(ctx(), m_opt, p); check_error(); }

src/api/dotnet/Optimize.cs

@@ -111,6 +111,26 @@ namespace Microsoft.Z3
             }         
         }
 
+        /// <summary>
+        /// Creates a backtracking point.
+        /// </summary>
+        /// <seealso cref="Pop"/>
+        public void Push()
+        {
+            Native.Z3_optimize_push(Context.nCtx, NativeObject);
+        }
+
+        /// <summary>
+        /// Backtrack one backtracking point.
+        /// </summary>
+        /// <remarks>Note that an exception is thrown if Pop is called without a corresponding <c>Push</c></remarks>
+        /// <seealso cref="Push"/>
+        public void Pop()
+        {
+            Native.Z3_optimize_pop(Context.nCtx, NativeObject);
+        }
+
+
         /// <summary>
         /// The model of the last <c>Check</c>.
         /// </summary>

src/api/python/z3.py

@@ -6382,6 +6382,14 @@ class Optimize(Z3PPObject):
 	"""Add objective function to minimize."""
 	return OptimizeObjective(Z3_optimize_minimize(self.ctx.ref(), self.optimize, arg.as_ast()))
 
+    def push(self):
+        """create a backtracking point for added rules, facts and assertions"""
+        Z3_optimize_push(self.ctx.ref(), self.optimize)
+
+    def pop(self):
+        """restore to previously created backtracking point"""
+        Z3_optimize_pop(self.ctx.ref(), self.optimize)
+
     def check(self):
 	"""Check satisfiability while optimizing objective functions."""
 	return CheckSatResult(Z3_optimize_check(self.ctx.ref(), self.optimize))

src/api/z3_api.h

@@ -6007,7 +6007,7 @@ END_MLAPI_EXCLUDE
 
 
     /**
-       \brief Add a maximiztion constraint.
+       \brief Add a maximization constraint.
        \param c - context
        \param o - optimization context
        \param a - arithmetical term       
@@ -6016,7 +6016,7 @@ END_MLAPI_EXCLUDE
     unsigned Z3_API Z3_optimize_maximize(Z3_context, Z3_optimize o, Z3_ast t);
 
     /**
-       \brief Add a minimiztion constraint.
+       \brief Add a minimization constraint.
        \param c - context
        \param o - optimization context
        \param a - arithmetical term   
@@ -6025,6 +6025,30 @@ END_MLAPI_EXCLUDE
     */
     unsigned Z3_API Z3_optimize_minimize(Z3_context, Z3_optimize o, Z3_ast t);
 
+
+    /**
+       \brief Create a backtracking point.
+       
+       The optimize solver contains a set of rules, added facts and assertions.
+       The set of rules, facts and assertions are restored upon calling #Z3_optimize_pop.
+
+       \sa Z3_optimize_pop
+
+       def_API('Z3_optimize_push', VOID, (_in(CONTEXT), _in(OPTIMIZE)))
+    */
+    void Z3_API Z3_optimize_push(Z3_context c,Z3_optimize d);
+
+    /**
+       \brief Backtrack one level.
+       
+       \sa Z3_optimize_push
+
+       \pre The number of calls to pop cannot exceed calls to push.
+
+       def_API('Z3_optimize_pop', VOID, (_in(CONTEXT), _in(OPTIMIZE)))
+    */
+    void Z3_API Z3_optimize_pop(Z3_context c,Z3_optimize d);
+
     /**
        \brief Check consistency and produce optimal values.
        \param c - context