code: def _detect(self):
          
          results = []
          for c in self.slither.contracts:
              for f in c.functions + c.modifiers:
                  if f.contract != c:
                      continue
                  unused_return = self.detect_unused_return_values(f)
                  if unused_return:
                      info = "{}.{} ({}) does not use the value returned by external calls:\n"
                      info = info.format(f.contract.name,
                                         f.name,
                                         f.source_mapping_str)
                      for node in unused_return:
                          info += "\t-{} ({})\n".format(node.expression, node.source_mapping_str)
  
                      json = self.generate_json_result(info)
                      self.add_function_to_json(f, json)
                      self.add_nodes_to_json(unused_return, json)
                      results.append(json)
  
          return results
docs: Detect high level calls which return a value that are never used