text: 
  #ifndef __GFCALLABLE_H
  #define __GFCALLABLE_H
  
  #include "Freeable.h"
  
  namespace Groundfloor {
  
  /** TGFCallable defines an abstruct function execute() that
    * other objects may call upon.
    */
  class Callable: public Groundfloor::Freeable
  {
      public:
           /// abstract function to implement
          virtual void execute() = 0;
  };
  
  }
  
  #endif // __GFCALLABLE_H
  