How to Read Code in Emacs

1 View

1.1 Highlight Code

Attachments: highlight%20code.png
ID: 98ca483b-70bd-4a8b-b1b9-d604672fb8f3

You can use highlighting tools to mark code with different colors like taking notes to distinguish code.

  • I used Emacs package symbol-overlay or other similar highlighting packages.

2 Navigation

2.1 Jump to definition of any code

There are some options to select:

  • Use text searching tools directly, Emacs isearch, grep, ag, pt, rg etc.
  • If you want advanced text searching, can use "regexp search", Emacs has built-in support, and has some packages to help you, even can use PCRE (Perl regexp) in Emacs with package "pcre2el".
  • In current buffer, you can use Imenu, etc to jump.
  • Or even open an class/functions definitions sidebar to have an overview of your code.

2.2 Jump to definition of thing-at-point

When code definition is not in the same window page area, you want to jump to definition. You can use xref.el (which is Emacs built-in support now). If you want to keep current code viewing, you can create a function to accept universal prefix argument C-u for [M-.] to open code definition in other window. If you don't want to mess your windows up, you also can try Emacs new feature (from 26?) "child-frame". There is an existing package called "posframe" can be helpful.

3 Figure out of Code by running it

Attachments: Edebug%20result%20at%20point.png
ID: 6c961996-eff9-41fa-a420-9272520996af

Sometimes I can't understand the code by reading, then I try to run code with debugger/tracer.

For example, Elisp code, Emacs has built-in tool Edebug.

Because Edebug show stop point result in echo-area (minibuffer). It is not convinient for me. I want it displayed at point.


Here is my trick after I dive into Edebug source code:

(defun my:edebug-previous-result ()
    "Print the previous result."
    ;; (pos-tip-show edebug-previous-result 'popup-face) ; slow
    (popup-tip edebug-previous-result :truncate t :height 20 :width 45 :nostrip t :margin 1 :nowait nil)
  (advice-add 'edebug-previous-result :override #'my:edebug-previous-result)

Tip: Sometimes edebug will auto scroll down, when stop point moves to bottom of window, the result popup is truncated, you can use C-l (recenter-top-bottom) to recenter window. Then redisplay result popup with [r].

About other programming languages, like C, C++, there are tools for static diagnostic as @MaskRay wiki mentioned, and dynamic diagnostic like cgdb (@MaskRay mentioned).

More programming languages has more relative tools. I will not list them one by one at here. Just give out some examples that wish can inspire you. That's all.

4 TODO Will add more tricks here in future

Record to My Org node "Read Code" too.