anchor.diff:        """);
       }
   
  -    writePrelude();
       var visitor = new JsAstVisitor(buff);
       visitor.visit(program);
   
  
positive.code:     _bodies.add(minify(body));
    }
  
    void addTopLevel(String name, String body) {
      _topLevel.add("var ${name} = ${body}");
    }
  
    List<String> _topLevel = [];
  
    void writePrelude() {
      if (_topLevel.isNotEmpty) {
        buff.write(_topLevel.join(";"));
        buff.write(";");
      }
      buff.write('(function(${_names.join(",")}){var λ = {"args": args};');
    }
  
    final RegExp _WHITESPACE = new RegExp(r'''\s{2,}(?=([^"]*("|')[^"']*("|'))*[^"']*$)''');
  
negative.code:       visitor.visitStatement(new MethodCall("runTests", []));
      }
  
      return minify(generatePrelude() + buff.toString() + generatePostlude());
    }
  
    void addGlobal(String name, String body) {
  