code: func excludeExecutable(goFiles []string) []string {
  	var s []string
  	for _, f := range goFiles {
  		if strings.HasPrefix(f, "executable_") {
  			continue
  		}
  		s = append(s, f)
  	}
  	return s
  }
docs: // excludeExecutable excludes all executable implementation .go files.
  // They have "executable_" prefix.