You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: mapper.go
    path of file: ./repos/gleam/gio
    
    the code of the file until where you have to start completion: package gio

import (
	"context"
	"fmt"
	"io"
	"os"

	"github.com/chrislusf/gleam/util"
)

func (runner *gleamRunner) processMapper(ctx context.Context, f Mapper) (err error) {
	return runner.report(ctx, func() error {
		return runner.doProcessMapper(ctx, f)
	})
}

func (runne
    
func (runner *gleamRunner) doProcessMapper(ctx context.Context, f Mapper) error {
	for {
		row, err := util.ReadRow(os.Stdin)
		if err != nil {
			if err == io.EOF {
				return nil
			}
			return fmt.Errorf("mapper input row error: %v", err)
		}
		stat.Stats[0].InputCounter++

		var data []interface{}
		data = append(data, row.K...)
		data = append(data, row.V...)
		err = f(data)
		if err != nil {
			return fmt.Errorf("processing error: %v", err)
		}
	}
	return nil
}