anchor.diff:      String dummy = names.name(node);
       String variable = names.name(node.variable.definition);
       String value = formatReference(node.value);
  -    printStmt(dummy, '${node.runtimeType} $variable := $value');
  +    printStmt(dummy, 'SetMutableVariable $variable := $value');
       visit(node.body);
     }
   
  
positive.code: 
    visitLetMutable(cps_ir.LetMutable node) {
      String id = names.name(node.variable);
      printStmt(id, "${node.runtimeType} $id = ${formatReference(node.value)}");
      visit(node.body);
    }
  
  
negative.code: 
    visitGetMutableVariable(cps_ir.GetMutableVariable node) {
      String variable = names.name(node.variable.definition);
      return 'GetMutableVariable $variable';
    }
  }
  
  