if self.product is Paths and type(subject) is PathGlobs:
        return Return(file_exists(step_context.project_tree, subject))
      elif self.product is FilesContent and type(subject) is Paths:
        return Return(files_content(step_context.project_tree, subject))
      elif self.product is DirectoryListing and type(subject) is Path:
        return Return(list_directory(step_context.project_tree, subject))
      else:
        return Noop('couldnt resolve product {} for subject {} in a FilesystemNode'
                    .format(self.product, subject))