public class OurEnvFactory extends QvtOperationalEnvFactory {
	
	@Override
	public EvaluationVisitor<stuff> createEvaluationVisitor(stuff)
	{
		return new QvtOperationalEvaluationVisitorImpl((QvtOperationalEnv)env, (QvtOperationalEvaluationEnv)evalEnv)
		{
			
			@Override
			public Object visitMappingOperation(MappingOperation mappingOperation)
			{
				// our new code here!
				
				return super.visitMappingOperation(mappingOperation);
			}
		};
	}
}

// And to actually execute

...
internalExecutor.setEnvironmentFactory(ourEnvFactory); // Instrumented visitor
ExecutionDiagnostic result = internalExecutor.execute(context1, input,output);
...

public class OurEnvFactory extends QvtOperationalEnvFactory {
	
	@Override
	public EvaluationVisitor<stuff> createEvaluationVisitor(stuff)
	{
		return new MyVisitorDecorator(new QvtOperationalEvaluationVisitorImpl((QvtOperationalEnv)env, (QvtOperationalEvaluationEnv)evalEnv));
	}
}


public class MyVisitorDecorator<stuff> extends EvaluationVisitorDecorator<stuff> {
// Would prefer not to implement InternalEvaluator since there are so many methods

	private QvtOperationalEvaluationVisitorImpl delegate;
	
    public MyVisitorDecorator(EvaluationVisitor<stuff> decorated) {
        super(decorated);
        if (decorated instanceof QvtOperationalEvaluationVisitorImpl) {
        	delegate = (QvtOperationalEvaluationVisitorImpl) decorated;
        }
    }
    
	public Object visitMappingOperation(MappingOperation mappingOperation)
	{
		return delegate.visitMappingOperation(mappingOperation); 
	}

class MyVisitorDecorator extends QvtGenericEvaluationVisitor {
	
	private QvtOperationalEvaluationVisitor delegate;

	public MyVisitorDecorator(QvtOperationalEvaluationVisitor qvtExtVisitor) {
		super(qvtExtVisitor);
		delegate = qvtExtVisitor;
	}

	public IContext getContext() {
		return delegate.getContext();
	}

	public void setOperationalEvaluationEnv(QvtOperationalEvaluationEnv evalEnv) {
		delegate.setOperationalEvaluationEnv(evalEnv);
	}

	public QvtOperationalEvaluationEnv getOperationalEvaluationEnv() {
		return delegate.getOperationalEvaluationEnv();
	}
	
}

public EvaluationVisitor<..> createEvaluationVisitor(...) {

	EvaluationVisitorDecorator<..> decorator = 
		new MyVisitorDecorator((QvtOperationalEvaluationVisitor) super.createEvaluationVisitor(env, evalEnv, extentMap)) {

		@Override
		public Object visitMappingBody(MappingBody mappingBody) {
			...
			return super.visitMappingBody(mappingBody);
		}
		
	};

	return decorator;
}

...
public class OurVisitor extends QvtOperationalEvaluationVisitorImpl implements InternalEvaluator, DeferredAssignmentListener {

	public OurVisitor (QvtOperationalEnv env, QvtOperationalEvaluationEnv evalEnv) {
		super(env, evalEnv);
	}
	
	@Override
	protected InternalEvaluator createInterruptibleVisitor() {
		return new OurDecorator(this);
	}
	
	protected class OurDecorator extends QvtGenericEvaluationVisitor implements InternalEvaluator{
		
		private QvtOperationalEvaluationVisitorImpl delegate;
		
		public OurDecorator(QvtOperationalEvaluationVisitorImpl qvtOperationalEvaluationVisitor) {
			super(qvtOperationalEvaluationVisitor);
			delegate = qvtOperationalEvaluationVisitor;
		}
		
		@Override
		protected Object genericPostVisitAST(ASTNode element,
				Object preVisitState, Object result) {
			
			// Do you interesting stuff here, or in visit* methods.
			
			return super.genericPostVisitAST(element, preVisitState, result);
		}

		@Override
		public IContext getContext() {
			return delegate.getContext();
		}

		@Override
		public void setOperationalEvaluationEnv(QvtOperationalEvaluationEnv evalEnv) {
			delegate.setOperationalEvaluationEnv(evalEnv);
		}

		@Override
		public QvtOperationalEvaluationEnv getOperationalEvaluationEnv() {
			return delegate.getOperationalEvaluationEnv();
		}

		@Override
		public ModuleInstance callTransformationImplicitConstructor(OperationalTransformation transformation, List<ModelInstance> args) {
			return delegate.callTransformationImplicitConstructor(transformation, args);
		}
		
		@Override
		public OperationCallResult runMainEntry(OperationalTransformation transformation, List<Object> args) {
			return delegate.runMainEntry(transformation, args);
		}

		@Override
		public Object execute(OperationalTransformation transformation) throws QvtRuntimeException {
			return delegate.execute(transformation);
		}
	}	
}

...

public class OurEnvFactory extends QvtOperationalEnvFactory{
	
	public QVTOCoverageEnvFactory() {
	}
	
	@Override
	public
	EvaluationVisitor<stuff> createEvaluationVisitor(stuff) {
		
		return new OurVisitor((QvtOperationalEnv) env, (QvtOperationalEvaluationEnv) evalEnv).createInterruptibleVisitor();
	}
}

...

public class OurExecutor extends InternalTransformationExecutor {

	public OurExecutor(URI uri) {
		super(uri);
	}

	@Override
	public ExecutionDiagnostic execute(ExecutionContext executionContext,
			ModelExtent... modelParameters) {
		
		setEnvironmentFactory(new OurEnvFactory());
		return super.execute(executionContext, modelParameters);
	}
}

public class MyQvtInterpretedTransformation extends QvtInterpretedTransformation {

	public MyQvtInterpretedTransformation(IFile transformationFile) {
		super(transformationFile);
		setEnvironmentFactory(new OurEnvFactory());
	}

	public MyQvtInterpretedTransformation(QvtModule qvtModule) {
		super(qvtModule);
		setEnvironmentFactory(new OurEnvFactory());
	}

}