adding callback hell to go, why not?

async.go

package main

import (
  "fmt"
  "io/ioutil"
  "log"
  "os"
  "sync"
)

func openAsync(fileName string, callback func([]byte, error)) {
  callback(ioutil.ReadFile(fileName))
}

func printContents(contents []byte, err error) {
  if err != nil {
    log.Fatal(err)
  }
  fmt.Printf("%s", contents)
}
func main() {
  var wg sync.WaitGroup
  arg := os.Args[1]

  wg.Add(1)
  go func() {
    defer wg.Done()
    openAsync(arg, printContents)
  }()
  wg.Wait()
}