Emacs：如何计算光标所在的最小 s 表达式，或以下 s 表达式

发布于 2024-08-19 22:41:46 字数 807 浏览 3 评论 0原文

评估中的 (+ 100 (+ 100 100)) 部分的好方法是什么

(+ (+ 1 2) (+ 100 (+ 100 100)))

？

目前，我通过 Cx Ce 进行操作，这意味着我需要找到结束括号，这在大多数情况下很困难。 选项> Paren 匹配突出显示 有帮助，但我仍然需要将光标移向结束括号，直到突出显示的匹配是开始括号。

一种方法是使用 Cx Ce 的反向版本，这样我就可以将光标放在起始括号处，如下所示：

(+ (+ 1 2) |(+ 100 (+ 100 100)))

然后按适当的键绑定。

或者，我可以将光标放在表达式内，但不能放在较小的表达式内：

(+ (+ 1 2) (+ | 100 (+ 100 100)))

然后按键绑定。因为目标越大，瞄准目标就越容易。

我怎样才能发出这样的命令？或者已经提供了吗？

旁注：条形光标和方框光标

使用方框光标（默认）的 Emacsers 可能想知道我将带有上面条形符号的光标放在哪里。在 emacs 中，您可以选择框光标或条光标，(bar-cursor-mode t)。当条形光标位于字母 A 和 B 之间时，框光标位于 B 上。因此，条形是框的左壁。

顺便说一句，条形光标的概念在一些不寻常的方面很有用：编程中从index1迭代到index2-1的做法让初学者感到惊讶。它有助于将索引 1 和索引 2 想象为指示条（左墙）而不是框。

原文

What is a good way to evaluate the (+ 100 (+ 100 100)) part in

(+ (+ 1 2) (+ 100 (+ 100 100)))

For now, I do it by C-x C-e, which means I need to locate the ending parenthesis, which is difficult in most cases. Options > Paren Matching Highlighting helps, but still I need to move the cursor toward the ending parenthesis until the highlighted match is the starting parenthesis.

One way would be to have the reverse version of C-x C-e, so that I can place the cursor at the starting parenthesis like this:

(+ (+ 1 2) |(+ 100 (+ 100 100)))

and then press the appropriate keybinding.

Or I could place the cursor inside the expression, but not inside smaller expressions,:

(+ (+ 1 2) (+ | 100 (+ 100 100)))

and press a keybinding. Because aiming at a target is easier if the target is big.

How can I make such a command? Or is there one already provided?

Sidenote: bar cursor and box cursor

Emacsers who use box cursor (default) might wonder where I'm putting the cursor with the bar notation above. In emacs, you can choose box cursor or bar cursor, (bar-cursor-mode t). When the bar cursor is between the letters A and B, the box cursor is on B. So the bar is the left wall of the box.

BTW, the concept of bar cursor is useful in some unusual way:
The practice of iterating from index1 to index2-1 in programming surprises beginners. It helps to imagine index1 and index2 as indicating bars (left walls) rather than boxes.

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玩心态 2024-08-26 22:41:46

将键绑定到其中一个或两个：

(defun eval-next-sexp ()
  (interactive)
  (save-excursion
    (forward-sexp)
    (eval-last-sexp nil)))

(defun eval-surrounding-sexp (levels)
  (interactive "p")
  (save-excursion
    (up-list (abs levels))
    (eval-last-sexp nil)))

切线相关，我强烈建议使用 paredit 来使用s-表达式。结构编辑命令和绑定使编辑 s 表达式变得轻而易举。它将 C-down 绑定到 up-list，这样上面的 eval-surrounding-sexp 几乎和 C-down Cx Ce 完全一样（唯一的区别是函数使用 save-excursion 来防止移动）。

Bind a key to one or both of these:

(defun eval-next-sexp ()
  (interactive)
  (save-excursion
    (forward-sexp)
    (eval-last-sexp nil)))

(defun eval-surrounding-sexp (levels)
  (interactive "p")
  (save-excursion
    (up-list (abs levels))
    (eval-last-sexp nil)))

Tangentially related, I highly recommend paredit for working with s-expressions. The structure editing commands and bindings make editing s-expressions a breeze. It binds C-down to up-list, so that eval-surrounding-sexp above is almost exactly the same as C-down C-x C-e (the only difference is that the function uses save-excursion to prevent movement).

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莫相离 2024-08-26 22:41:46

你可以这样写这样的命令：

(require 'thingatpt)
(defun eval-sexp-at-or-surrounding-pt ()
  "evaluate the sexp following the point, or surrounding the point"
  (interactive)
  (save-excursion
    (forward-char 1)
    (if (search-backward "(" nil t)
        (message "%s" (eval (read-from-whole-string (thing-at-point 'sexp)))))))

You could write such a command like so:

(require 'thingatpt)
(defun eval-sexp-at-or-surrounding-pt ()
  "evaluate the sexp following the point, or surrounding the point"
  (interactive)
  (save-excursion
    (forward-char 1)
    (if (search-backward "(" nil t)
        (message "%s" (eval (read-from-whole-string (thing-at-point 'sexp)))))))

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