src/Language/Parser.php
private function parseOperationTypeDefinition()
    {
        $start     = $this->lexer->token;
        $operation = $this->parseOperationType();
        $this->expect(Token::COLON);
        $type = $this->parseNamedType();

        return new OperationTypeDefinitionNode([
            'operation' => $operation,
            'type'      => $type,
            'loc'       => $this->loc($start),
        ]);
    }
private function parseOperationTypeDefinition()
    {
        $start     = $this->lexer->token;
        $operation = $this->parseOperationType();
        $this->expect(Token::COLON);
        $type = $this->parseNamedType();

        return new OperationTypeDefinitionNode([
            'operation' => $operation,
            'type'      => $type,
            'loc'       => $this->loc($start),
        ]);
    }
@return OperationTypeDefinitionNode

@throws SyntaxError