funcsAO.go
func CharAtF(index int) func(string) string {
	return func(s string) string {
		return CharAt(s, index)
	}
}
func CharAtF(index int) func(string) string {
	return func(s string) string {
		return CharAt(s, index)
	}
}
// CharAtF is the filter form of CharAt.