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: starlark.go
    path of file: ./repos/gdlv
    
    the code of the file until where you have to start completion: package main

import (
	"fmt"
	"io"
	"io/ioutil"
	"os"

	"go.starlark.net/starlark"

	"github.com/aarzilli/gdlv/
    
func (s starlarkContext) RegisterCallback(name, helpMsg string, fn func(args string) (starlark.Value, error)) {
	cmdfn := func(out io.Writer, args string) error {
		defer refreshState(refreshToFrameZero, clearStop, nil)
		v, err := fn(args)
		if err != nil {
			return err
		}
		fmt.Fprintf(out, "%v\n", v)
		return nil
	}

	found := false
	for i := range cmds.cmds {
		cmd := &cmds.cmds[i]
		for _, alias := range cmd.aliases {
			if alias == name {
				cmd.cmdFn = cmdfn
				cmd.helpMsg = helpMsg
				found = true
				break
			}
		}
		if found {
			break
		}
	}
	if !found {
		newcmd := command{
			aliases: []string{name},
			helpMsg: helpMsg,
			cmdFn:   cmdfn,
			group:   scriptCmds,
		}
		cmds.cmds = append(cmds.cmds, newcmd)
	}
}