// error writing to its output. We strip the wrapper in errRecover.
// Note that this is not an implementation of error, so it cannot escape
// from the package as an error value.
type writeError struct {
	Err error // Original error.
}

func (s *state) writeError(err error) {
	panic(writeError{
		Err: err,
	})
}

// errRecover is the handler that turns panics into returns from the top