code: def parse_operation_type_definition(lexer: Lexer) -> OperationTypeDefinitionNode:
      
      start = lexer.token
      operation = parse_operation_type(lexer)
      expect_token(lexer, TokenKind.COLON)
      type_ = parse_named_type(lexer)
      return OperationTypeDefinitionNode(
          operation=operation, type=type_, loc=loc(lexer, start)
      )
docs: OperationTypeDefinition: OperationType : NamedType