How to Edit Lisp Code with Emacs

By Xah Lee. Date: . Last updated: .

This page is a tutorial on using emacs's default features to edit lisp code, or any text with matching brackets.

Auto Highlight Parenthesis: show-paren-mode

Emacs: Auto Highlight Parenthesis: show-paren-mode

Inserting Brackets by Pairs

Emacs: Insert Parenthesis by Pair: electric-pair-mode

Navigating Nested Code

Lisp code with its nested parenthesis syntax represents a tree structure.

Emacs has many commands that are very helpful in moving around nested brackets, analogous to navigating a tree.

(For historical reasons, lisp code are called “sexp”, short for Symbolic EXPression.)

lisp code navigation commands
Ctrl+Alt+backward-sexpMove to previous sibling
(move to the (beginning of) previous sexp unit)
Ctrl+Alt+forward-sexpMove to next sibling
(move to the (end of) next sexp unit)
Ctrl+Alt+backward-up-listMove to parent
(move to the (beginning of) outer paren pair)
Ctrl+Alt+down-listMove to first child
(move into the (beginning of) first inner paren pair)

The following is lisp source code laid out in a way to show its tree structure. You should try the above commands on it. It is very helpful to understand how sexp corresponds to a tree, and how the commands move the cursor exactly.

  (f x li)
  "Applies (f x ele) recursively to the list li …"
      (li2 li)
      (x2 x)
      (setq ele (pop li2))
      (setq x2 (funcall f x2 ele))

Place your cursor at the beginning of the left bracket. Now, try to move your cursor, by using ONLY 【Ctrl+Alt+arrow】, to the “pop” , then move it to “let”, then “funcall”.

Moving to Previous/Next Sibling that Has Children

Use backward-list and forward-list to jump to prev/next sibling that has children. (i.e. skip siblings that does not have children.)

For example, suppose you have (a (b) ▮ c d (e f)) and your cursor is before “c”. Then:

Freely Moving Cursor to Brackets

It's also very convenient to have keys that moves to any prev/next opening/closing bracket characters, without regarding the tree structure.

See: Emacs: Move Cursor to Brackets, Quotes.

Selecting Lisp Code by Unit

You can use the command mark-sexpCtrl+Alt+Space】 to select a complete sexp. Your cursor must be on the left bracket.

To select a complete sexp, type 【Ctrl+Alt+】 then 【Ctrl+Alt+Space】.

Backward/Forward Code Section

Emacs: How to Move Cursor Around Source Code Section (^L)

Show lambda as λ

Emacs: Display Lambda as λ

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