code: func LazyHandler(h LogHandler) LogHandler {
  	return FuncHandler(func(r *Record) error {
  		for k, v := range r.Context {
  			if lz, ok := v.(Lazy); ok {
  				value, err := evaluateLazy(lz)
  				if err != nil {
  					r.Context[errorKey] = "bad lazy " + k
  				} else {
  					v = value
  				}
  			}
  		}
  
  		return h.Log(r)
  	})
  }
docs: // LazyHandler writes all values to the wrapped handler after evaluating
  // any lazy functions in the record's context. It is already wrapped
  // around StreamHandler and SyslogHandler in this library, you'll only need
  // it if you write your own Handler.