为什么某些Emacs功能不能通过`M-x'？ [英] Why are some Emacs functions not available via `M-x`?

问题描述

，它可以输入命令的名称并运行它。

M - ：绑定到命令 eval-expression ，它允许您键入包含函数调用的任意S表达式，并对其进行评估。 / li>

可以使用 M调用的功能：用于实现Emacs功能，自定义如您的 .emacs ）和插件。函数参数通常通过调用S表达式中的函数传递。

任何函数都可以作为命令，如果它有一个 interactive 在其定义中形成。 交互式表格描述了当作为命令调用时该函数应该如何获取其参数。例如，如果函数在其定义中具有（交互式bGive me a buffer：），则该函数将使用 M-x 进行调用。当用户使用 Mx 调用该功能时，Emacs将提示用户输入一个缓冲区名称（因为 b ）和它们键入的名称将作为一个参数传递给函数。

使函数成为一个命令的重点在于使最终用户更容易调用它，而不仅仅是为了Emacs Lisp程序员。命令（使用 Mx 运行）通过以下方式更容易以交互方式运行：

• 您不必使用（）包含命令名称，使其成为有效的S表达式。


• 可以自动传递参数（如光标位置），或者您可以提示他们，以便您不必记住需要什么参数。


• 当提示输入参数时，您可以自动完成，因为 interactive form的代码字符（如 b ）指定要预期的输入类型。

您不能使用 Mx 调用函数 set-face-attribute 的原因是它的定义不包含交互式表单，因此 set-face-attribute 不是一个命令。您必须将其称为简单函数，在S表达式中。您可以使用 M - ：的minibuffer或其他任何其他评估代码的方法。

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Emacs Mini手册→概念→命令对于正常功能和命令之间的差异有一个简短的，不同的措辞。 Emacs功能和命令之间的关系解释了这个答案中的一些细节。

This Stack Overflow answer told me that I can set Emacs’s font size with set-face-attribute:

(set-face-attribute 'default nil :height 100)

The comments reveal that you can’t run set-face-attribute with M-x:

Instead, you have to run it with M-::

Why are some commands, like set-face-attribute, not available via M-x?

解决方案

• M-x is bound to the command execute-extended-command, which lets you type the name of a command and runs it.
• M-: is bound to the command eval-expression, which lets you type an arbitrary S-expression containing function calls and evaluates it.

Functions, which you can call with M-:, are used to implement Emacs features, customizations (such as in your .emacs), and plugins. Function arguments are normally passed by calling the function in an S-expression.

Any function can also be a command if it has an interactive form in its definition. The interactive form describes how the function should get its arguments when called as a command. For example, if the function has (interactive "bGive me a buffer: ") in its definition, then the function will be callable with M-x. When the user calls the function with M-x, Emacs will prompt the user for a buffer name (because of the b), and the name they type will be passed as an argument to the function.

The point of making a function a command is to make calling it easy for end-users, not just for Emacs Lisp programmers. Commands (run with M-x) are easier to run interactively in these ways:

• You don’t have to surround the command name with () to make it a valid S-expression.
• Arguments can be passed automatically (such as the cursor position), or you can be prompted for them so you don’t have to remember what arguments are needed.
• When prompted for an argument, you can auto-complete it, because the interactive form’s code characters (like b) specify what type of input to expect.

The reason you can’t call the function set-face-attribute with M-x is that its definition does not contain an interactive form, and so set-face-attribute is not a command. You must call it as a plain function, in S-expressions. You can do that from the minibuffer with M-:, or from other places with any of the other ways of evaluating code.

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Emacs Mini Manual → Concepts → Command has a short, differently-worded explanation of the difference between normal functions and commands. Relationship between Emacs functions and commands explains some details not in this answer.

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