As others have said, it's idiomatic to name a lambda param "_" if you're not using it.

To perhaps clarify a bit, here's what the Hello World example would look like if we added a second route that uses the lambda parameter, and a third route that does something else, and a fourth route that renders a view template.

  public SampleModule() { 
    Get["/"] = _ => "Hello World!"; 

    Get["/hello/{name}"] = p => ("Hello, " + p.name + "!");

    Get["/something-complicated"] = _ => {
      // complicated stuff happens here
      return "OK... we're all done";
    };

    // A variety of template engines are supported
    Get["/my-resume"] = _ => View["resume.cshtml"];
   
  }