code: func (i *interpreter) manifestString(buf *bytes.Buffer, trace TraceElement, v value) error {
  	switch v := v.(type) {
  	case *valueString:
  		buf.WriteString(v.getString())
  		return nil
  	default:
  		return makeRuntimeError(fmt.Sprintf("expected string result, got: %s", v.getType().name), i.getCurrentStackTrace(trace))
  	}
  }
docs: // manifestString expects the value to be a string and returns it.