Elisp snippets

Snippets

Execute command in shell buffer

comint-send-string is the function we’re looking for.¹

It takes a PROCESS and a STRING. You can get the process from the shell buffer, and conveniently the shell function returns the buffer, so you can streamline it all into something like:

(defun my-server ()
  "SSH to my.server.com in `shell' buffer."
  (interactive)
  (comint-send-string
   (get-buffer-process (shell))
   "ssh my.server.com\n"))

Where the (shell) call will take care of creating the shell buffer and/or process if necessary.²

Free variables

In some situations, for instance when setting a variable in a DOOM Emacs like

(setq my/variable "value")

You might get the warning

Warning: assignment to free variable `er/try-expand-list'

This is because set and setq do not declare lexical variables³. The solution is to use⁴

(defvar my/variable "value")

Lists to arrays

List of lists

To convert a list of lists, e.g.

(defvar mylist (("1" "a") ("2" "b") ("3" "c")))

The method to convert a single element from the list is

(require 'cl)
 (coerce (nth 0 mylist) 'vector)
 ;; ["1" "a"]

We now just need to map this for all the list

(mapcar (lambda (arg) (coerce arg 'vector)) mylist) 

Lists conversion

To convert a vector to list:

(coerce [1 2 3] 'list)
;; (1 2 3)

and to convert a list to vector:

(coerce '(1 2 3) 'vector)
;; [1 2 3]

Reference

defcustom

You can specify variables using defcustom so that you and others can then use Emacs’s customize feature to set their values. (You cannot use customize to write function definitions; but you can write defuns in your .emacs file. Indeed, you can write any Lisp expression in your .emacs~ file.)⁵

Footnotes

SQLite

Emacs provides functionality to interact with SQLite databases. For these examples we will use the emacSQL package. To open a database file /tmp/foo.sqlite we issue:

(defvar db (emacsql-sqlite "~/tmp/foo.sqlite"))

We can then issue SELECT statements with

;; Query the database for results:
 (emacsql db [:select [name id]
            :from people
            :where (> salary 62000)])
 ;; => (("Susan" 1001))