public AST <Node> EmitZingSideEffects(AST <Node> stmt)
            {
                Debug.Assert(sideEffectsStack.Count > 0);
                var sideEffects = sideEffectsStack.Pop();

                if (sideEffects.Count > 0)
                {
                    sideEffects.Add(stmt);
                    return(PToZing.MkZingSeq(sideEffects));
                }
                else
                {
                    return(stmt);
                }
            }
            public AST <Node> EmitLabelPrelude()
            {
                var prelude = new List <AST <Node> >();
                var tmpVar  = GetTmpVar(Factory.Instance.MkCnst("StackFrame"), "retTo");

                prelude.Add(PToZing.MkZingAssign(tmpVar, PToZing.MkZingCall(MkZingDot("entryCtxt", "PopReturnTo"))));
                prelude.Add(PToZing.MkZingAssign(MkZingIdentifier("locals"), MkZingDot(tmpVar, "locals")));
                prelude.Add(PToZing.MkZingIfThen(PToZing.MkZingEq(MkZingDot(tmpVar, "pc"), Factory.Instance.MkCnst(0)), MkZingGoto("start")));

                foreach (var l in labels.Keys)
                {
                    prelude.Add(PToZing.MkZingIfThen(PToZing.MkZingEq(MkZingDot(tmpVar, "pc"), Factory.Instance.MkCnst(labels[l])), MkZingGoto(l)));
                }

                prelude.Add(MkZingAssert(ZingData.Cnst_False, "Internal error"));

                return(PToZing.MkZingSeq(prelude));
            }