Boo.Lang.Compiler.Steps.GeneratorExpressionProcessor.CreateMoveNext C# (CSharp) Метод

        void CreateMoveNext()
        {
            BooMethodBuilder method = _enumerator.AddVirtualMethod("MoveNext", TypeSystemServices.BoolType);

            Expression moveNext = CodeBuilder.CreateMethodInvocation(
                CodeBuilder.CreateReference((InternalField)_enumeratorField.Entity),
                TypeSystemServices.Map(Types.IEnumerator.GetMethod("MoveNext")));

            Expression current = CodeBuilder.CreateMethodInvocation(
                CodeBuilder.CreateReference((InternalField)_enumeratorField.Entity),
                ((IProperty)GetMember(_sourceEnumeratorType, "Current", EntityType.Property)).GetGetMethod());

            Statement filter = null;
            Statement stmt = null;
            Block outerBlock = null;
            Block innerBlock = null;

            if (null == _generator.Filter)
            {
                IfStatement istmt = new IfStatement(moveNext, new Block(), null);
                outerBlock = innerBlock = istmt.TrueBlock;

                stmt = istmt;
            }
            else
            {
                WhileStatement wstmt = new WhileStatement(moveNext);
                outerBlock = wstmt.Block;

                if (StatementModifierType.If == _generator.Filter.Type)
                {
                    IfStatement ifstmt = new IfStatement(_generator.Filter.Condition, new Block(), null);
                    innerBlock = ifstmt.TrueBlock;
                    filter = ifstmt;
                }
                else
                {
                    UnlessStatement ustmt = new UnlessStatement(_generator.Filter.Condition);
                    innerBlock = ustmt.Block;
                    filter = ustmt;
                }

                stmt = wstmt;
            }

            DeclarationCollection declarations = _generator.Declarations;
            if (declarations.Count > 1)
            {
                NormalizeIterationStatements.UnpackExpression(CodeBuilder,
                                                method.Method,
                                                outerBlock,
                                                current,
                                                declarations);

                foreach (Declaration declaration in declarations)
                {
                    method.Locals.Add(((InternalLocal)declaration.Entity).Local);
                }
            }
            else
            {
                InternalLocal local = (InternalLocal)declarations[0].Entity;
                method.Locals.Add(local.Local);
                outerBlock.Add(CodeBuilder.CreateAssignment(
                                CodeBuilder.CreateReference(local),
                                current));
            }

            if (null != filter)
            {
                outerBlock.Add(filter);
            }

            innerBlock.Add(CodeBuilder.CreateAssignment(
                                CodeBuilder.CreateReference((InternalField)_current.Entity),
                                _generator.Expression));
            innerBlock.Add(new ReturnStatement(new BoolLiteralExpression(true)));

            method.Body.Add(stmt);
            method.Body.Add(new ReturnStatement(new BoolLiteralExpression(false)));
        }