Example of an error list in Go. https://play.golang.org/p/MLWS5UhxI11

errorlist.go

package main

import (
	"fmt"
	"math/rand"
	"strings"
)

type ErrorList []error

func (el ErrorList) Error() string {
	s := make([]string, 0, len(el))
	for _, e := range el {
		s = append(s, e.Error())
	}
	return strings.Join(s, ", ")
}

func main() {
	err := validate()
	if err != nil {
		fmt.Println(err)
	}
}

func validate() error {
	var errList ErrorList
	if err := subValidate("field"); err != nil {
		errList = append(errList, err)
	}
	if err := subValidate("value"); err != nil {
		errList = append(errList, err)
	}
	return errList
}

func subValidate(ctx string) error {
	var errList ErrorList
	for i := 0; i < 30; i++ {
		if err := maybeError(ctx, i); err != nil {
			errList = append(errList, err)
		}
	}
	return errList
}

func maybeError(ctx string, i int) error {
	if rand.Intn(3) == 1 {
		return fmt.Errorf("invalid %s %d", ctx, i)
	}
	return nil
}