为什么运行 `f <- function(x){x} %>% f` 不会抛出错误？

如何解决为什么运行 `f <- function(x){x} %>% f` 不会抛出错误？

R 在运行时不会抱怨：

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap.min.css">
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="col-sm-12 col-md-10 col-md-offset-1">
  <table class="table table-hover">
    <thead>
      <tr>
        <th>Product</th>
        <th>Restaurant</th>
        <th>Quantity</th>
        <th class="text-center">Price</th>
        <th class="text-center">Total</th>
        <th> </th>
      </tr>
    </thead>
    <tbody>
      <tr>
        <td class="col-sm-8 col-md-6">
          <div class="media">
            <a class="thumbnail pull-left" href="#"> <img class="media-object" src="http://icons.iconarchive.com/icons/custom-icon-design/flatastic- 
  2/72/product-icon.png" style="width: 72px; height: 72px;"> </a>
            <div class="media-body">
              <h4 class="media-heading">
                <a href="#">
              Abc
                </a>
              </h4>
              <h5 class="media-heading"> by
                <a href="#">
                Astar
                </a>
              </h5>
              <span>Status: </span><span class="text-warning"><strong>Good</strong></span>
            </div>
          </div>
        </td>
        <td class="col-md-1 text-left"><strong class="label label- 
  danger">None</strong></td>
        <td class="col-sm-1 col-md-1" style="text-align: center">
          <input type="email" class="form-control qty" name="qty" value="">
        </td>
        <td class="col-sm-1 col-md-1 text-center"><strong class="prodprice">55</strong></td>
        <td class="col-sm-1 col-md-1 text-center"><strong class="prodtotal"></strong></td>
        <td class="col-sm-1 col-md-1">
          <button type="button" class="btn btn-danger">
  <span class="fa fa-remove"></span> Remove
  </button></td>
      </tr>
      <tr>
        <td class="col-sm-8 col-md-6">
          <div class="media">
            <a class="thumbnail pull-left" href="#"> <img class="media-object" src="http://icons.iconarchive.com/icons/custom-icon-design/flatastic- 
  2/72/product-icon.png" style="width: 72px; height: 72px;"> </a>
            <div class="media-body">
              <h4 class="media-heading">
                <a href="#">
                Abc1
                </a>
              </h4>
              <h5 class="media-heading"> by
                <a href="#">
                A star 3
                </a>
              </h5>
              <span>Status: </span><span class="text-warning"><strong>ok</strong></span>
            </div>
          </div>
        </td>
        <td class="col-md-1 text-left"><strong class="label label- 
  danger">None</strong></td>
        <td class="col-sm-1 col-md-1" style="text-align: center">
          <input type="email" class="form-control qty" name="qty" value="">
        </td>
        <td class="col-sm-1 col-md-1 text-center"><strong class="prodprice">77</strong></td>
        <td class="col-sm-1 col-md-1 text-center"><strong class="prodtotal"></strong></td>
        <td class="col-sm-1 col-md-1">
          <button type="button" class="btn btn-danger">
  <span class="fa fa-remove"></span> Remove
  </button></td>
      </tr>
      <tr>
        <td> </td>
        <td> </td>
        <td> </td>
        <td>
          <h5>Subtotal</h5>
        </td>
        <td class="text-right">
          <!--just add this class-->
          <h5><strong class="subtotal">$999.99</strong></h5>
        </td>
      </tr>
      <tr>
        <td> </td>
        <td> </td>
        <td> </td>
        <td>
          <h5>Estimated shipping</h5>
        </td>
        <td class="text-right">
          <h5><strong>$9.999.99</strong></h5>
        </td>
      </tr>
      <tr>
        <td> </td>
        <td> </td>
        <td> </td>
        <td>
          <h3>Total</h3>
        </td>
        <td class="text-right" id="total">
          <h3><strong>$9.999.99</strong></h3>
        </td>
      </tr>
      <tr>
        <td> </td>
        <td> </td>
        <td> </td>
        <td>
          <button type="button" class="btn btn-default">
    <span class="fa fa-shopping-cart"></span> Continue Shopping
    </button></td>
        <td>

          <a href="<?PHP echo base_url('admin/checkout') ?>"><button type="button" 
    class="btn btn-success" >
     Checkout <span class="fa fa-play"></span></a>
          </button>
        </td>
      </tr>
    </tbody>
  </table>
</div>

（但运行 library(magrittr) f <- function(x){x} %>% f 会引发 C 堆栈错误）。

然而，它不等同于：

f(1)

哪个抛出错误 f <- f(function(x){x}) ？

为什么第一个命令不抛出错误？

解决方法

function 的绑定强度低于中缀运算符 %>%。这意味着您的代码等效于

f <- function(x) ({x} %>% f)

而不是

f <- (function(x) {x}) %>% f

后者确实会引发您所期望的错误。

,

这相当于：

f <- function(x) f(x)

并导致无限递归调用

,

啊，我明白了：

> body(f)
{
    x
} %>% f

实际上这相当于 f <- function(x){{x} %>% f}。