code: func (s scope) lookup(k string) data.Value {
  	for i := range s {
  		var elem = s[len(s)-i-1].vars
  		if val, ok := elem[k]; ok {
  			return val
  		}
  	}
  	return data.Undefined{}
  }
docs: // lookup checks the variable scopes, deepest out, for the given key