The Emacs Package Developer's Handbook

Table of Contents

After developing some little Emacs packages for a year or so, I began to notice how I'd forget little things that I learned, and then I'd have to go hunting for that information again. I also noticed how there are some issues for which there doesn't seem to be a "best practice" or "Standard Operating Procedure" to refer to.

So this is intended to be a place to collect and organize information related to Emacs package development. Built with Emacs, by Emacs package developers, for Emacs package developers.

You can read this Org file directly on the repository rendered by GitHub (which lacks support for some features of the document, such as links between sections), or you can read the HTML version.

Note: The primary sections are listed at the top of the page in the horizontal bar.

Emacs Lisp   elisp

Animations / Screencasts   animations screencasts video

Tools   tools

emacs-gif-screencast   GIFs

Most Emacs screencasts are done by first recording a video, then converting it to a GIF. It seems like a waste of resources considering the little animation Emacs features.

Most of the time, one user action equals one visual change. By exploiting this fact, this package tailors GIF-screencasting for Emacs and captures one frame per user action. It’s much more efficient than capturing frames even at a frequency as low as 10 per second. You could roughly expect 3 to 10 times smaller files compared to videos of the same quality. (Benchmarks are welcome.)

Another neat perk of action-based captures is that it produces editable GIF files: programs such as Gifsicle or The GIMP can be used to edit the delays or rearrange frames. This is particularly useful to fix mistakes in “post-processing”, without having to record the demo all over again.

Asynchronicity   async

Binding   scope binding

Information related to variable scope and binding in elisp code (e.g. lexical vs. dynamic scope).

Articles   articles

Make Flet Great Again « null program   macros flet letf

Chris Wellons explains how the old cl macro flet changes in its new cl-lib version, cl-flet, and how to use cl-letf to achieve the old functionality. It's a way to override functions in both lexical and dynamic scope, which is especially useful for unit testing.

Libraries   libraries

thunk   built_in

Thunk provides functions and macros to delay the evaluation of forms.

Use thunk-delay to delay the evaluation of a form (requires lexical-binding), and thunk-force to evaluate it. The result of the evaluation is cached, and only happens once.

Here is an example of a form which evaluation is delayed:

(setq delayed (thunk-delay (message "this message is delayed")))

delayed is not evaluated until thunk-force is called, like the following:

(thunk-force delayed)

This file also defines macros thunk-let and thunk-let* that are analogous to let and let* but provide lazy evaluation of bindings by using thunks implicitly (i.e. in the expansion).

Tools   tools

Lexical binding   built_in lexical_binding

Buffers   buffers

Best practices   best_practices

Inserting strings   strings

Inserting strings into buffers with insert is generally fast, but it can slow down in buffers with lots of markers or overlays. In general, it can be faster to insert one large string (which may include newlines). For example:

(let ((strings (cl-loop for i from 1 to 1000
                        collect (number-to-string i))))
  (garbage-collect)
  (--sort (< (caddr it) (caddr other))
          (cl-loop for times in '(1 10 100)
                   append (a-list "(loop do (insert ..."
                                  (cons times
                                        (benchmark-run-compiled times
                                          (with-temp-buffer
                                            (cl-loop for string in strings
                                                     do (insert string)))))
                                  "(apply #'insert ..."
                                  (cons times
                                        (benchmark-run-compiled times
                                          (with-temp-buffer
                                            (apply #'insert strings))))
                                  "(insert (apply #'concat ..."
                                  (cons times
                                        (benchmark-run-compiled times
                                          (with-temp-buffer
                                            (insert (apply #'concat strings)))))))))
(insert (apply #'concat … 100 0.000142085 0 0.0
(insert (apply #'concat … 10 0.000161172 0 0.0
(insert (apply #'concat … 1 0.00018764 0 0.0
(apply #'insert … 10 0.000665472 0 0.0
(apply #'insert … 100 0.000678471 0 0.0
(apply #'insert … 1 0.000755329 0 0.0
(loop do (insert … 10 0.000817031 0 0.0
(loop do (insert … 100 0.000869779 0 0.0
(loop do (insert … 1 0.001490397 0 0.0

The fastest method here is to call insert once with the result of calling concat once, using apply to pass all of the strings. With 100 iterations, it's about 6x faster than the next-fastest method, and even with 1 iteration, it's over 2x faster.

Libraries   libraries

bui.el: Buffer interface library

BUI (Buffer User Interface) is an Emacs library that can be used to make user interfaces to display some kind of entries (like packages, buffers, functions, etc.). The intention of BUI is to be a high-level library which is convenient to be used both by:

package makers, as there is no need to bother about implementing routine details and usual features (like buffer history, filtering displayed entries, etc.);

users, as it provides familiar and intuitive interfaces with usual keys (for moving by lines, marking, sorting, switching between buttons); and what is also important, the defined interfaces are highly configurable through various generated variables.

Checkers / linters   linters checkers

TODO Flycheck-package

Collections (lists, vectors, hash-tables, etc.)   collections

Best practices   best_practices

Filtering a list

Using -select from dash.el seems to be the fastest way:

(let ((list (cl-loop for i from 1 to 1000
                     collect i)))
  (bench-multi :times 100
    :ensure-equal t
    :forms (("(-non-nil (--map (when ..." (-non-nil
                                           (--map (when (cl-evenp it) it) list)))
            ("(delq nil (--map (when ..." (delq nil
                                                (--map (when (cl-evenp it) it) list)))
            ("cl-loop" (cl-loop for i in list
                                when (cl-evenp i)
                                collect i))
            ("-select" (-select #'cl-evenp list))
            ("cl-remove-if-not" (cl-remove-if-not #'cl-evenp list))
            ("seq-filter" (seq-filter #'cl-evenp  list)))))
Form x faster than next Total runtime # of GCs Total GC runtime
-select 1.17 0.01540391 0 0.0
cl-loop 1.05 0.01808226 0 0.0
seq-filter 1.13 0.01891708 0 0.0
(delq nil (–map (when … 1.15 0.02134727 0 0.0
cl-remove-if-not 1.18 0.02459478 0 0.0
(-non-nil (–map (when … slowest 0.02903999 0 0.0

Examples   examples

Alists   alists
Creation
;;;; Built-in methods

(list (cons 'one 1) (cons 'two 2))  ;; => ((one . 1) (two . 2))

'((one . 1) (two . 2))  ;; => ((one . 1) (two . 2))

(let ((numbers (list)))
  (map-put numbers 'one 1)
  (map-put numbers 'two 2))  ;; => ((two . 2) (one . 1))


;;;; Packages

;; `a-list' from a.el is the best way to make a new alist.

(a-list 'one 1
        'two 2)  ;; => ((one . 1) (two . 2))
Adding to
Single elements
;;;; Built-in methods

;; `map-put' is the best built-in way.  Requires Emacs 25.1+.

(let ((numbers (list (cons 'one 1))))
  (map-put numbers 'two 2)
  numbers)  ; => ((two . 2) (one . 1))

;; More primitive methods

;; Not recommended, but not too complicated:
(let ((numbers (list (cons 'one 1)))
      (more-numbers (a-list 'two 2
                            'three 3)))
  (append numbers more-numbers)) ;; => ((one . 1) (two . 2) (three . 3))

;; Don't do it this way, but it does demonstrate list/cons-cell
;; structure:
(let ((numbers (list (cons 'one 1))))
  (cons (cons 'three 3)
        (cons (cons 'two 2)
              numbers)))  ;; => ((three . 3) (two . 2) (one . 1))
Multiple elements
;;;; Built-in methods

;; `map-merge': if you're restricted to built-in packages, this works
;; well (requires Emacs 25.1+):
(let ((numbers (list (cons 'one 1)))
      (more-numbers (a-list 'two 2
                            'three 3)))
  (map-merge 'list numbers more-numbers))  ;; => ((three . 3) (two . 2) (one . 1))


;; Without map.el, you could use `append':
(let ((numbers (list (cons 'one 1)))
      (more-numbers (a-list 'two 2
                            'three 3)))
  (append numbers more-numbers)) ;; => ((one . 1) (two . 2) (three . 3))

;;;; Packages

;; `a-merge' from a.el is probably the best way:
(let ((numbers (list (cons 'one 1)))
      (more-numbers (a-list 'two 2
                            'three 3)))
  (a-merge numbers more-numbers))  ;; => ((three . 3) (two . 2) (one . 1))

Libraries   libraries

ht.el: The missing hash table library   hash_tables

This library provides a consistent and comprehensive set of functions for working with hash tables: they're named consistently, take a natural and consistent argument order, and cover operations that the standard Emacs functions don't.

list-utils: List-manipulation utility functions   lists

Similar to dash.el, but with slightly different behavior that may be useful, and some unique features. These functions are provided:

make-tconc list-utils-depth
tconc-p list-utils-flat-length
tconc-list list-utils-flatten
tconc list-utils-alist-or-flat-length
list-utils-cons-cell-p list-utils-alist-flatten
list-utils-cyclic-length list-utils-insert-before
list-utils-improper-p list-utils-insert-after
list-utils-make-proper-copy list-utils-insert-before-pos
list-utils-make-proper-inplace list-utils-insert-after-pos
list-utils-make-improper-copy list-utils-and
list-utils-make-improper-inplace list-utils-not
list-utils-linear-p list-utils-xor
list-utils-linear-subseq list-utils-uniq
list-utils-cyclic-p list-utils-dupes
list-utils-cyclic-subseq list-utils-singlets
list-utils-make-linear-copy list-utils-partition-dupes
list-utils-make-linear-inplace list-utils-plist-reverse
list-utils-safe-length list-utils-plist-del
list-utils-safe-equal  

Data structure   data_structure

Date / Time   dates times

Libraries   libraries

emacs-datetime

The primary function provided is: (datetime-format SYM-OR-FMT &optional TIME &rest OPTION)

(datetime-format "%Y-%m-%d")  ;=> "2018-08-22"
(datetime-format 'atom)  ;=> "2018-08-22T18:23:47-05:00"
(datetime-format 'atom "2112-09-03 00:00:00" :timezone "UTC")  ;=> "2112-09-03T00:00:00+00:00"

There are several other symbols provided besides atom, such as rfc-3339, which formats dates according to that RFC.

Debugging   debugging

Tools   tools

Edebug   Edebug

Edebug is a built-in stepping debugger in Emacs. It's thoroughly documented in the elisp manual.

Declaring debug forms for keyword arguments   tip

Declaring debug forms for functions and macros that take keyword arguments can be confusing. Here's a contrived example:

(cl-defmacro make-fn (name docstring &key args bindings body)
  (declare (indent defun)
           (debug (&define symbolp stringp
                           &rest [&or [":body" def-form] [keywordp listp]])))
  `(defun ,name ,args
     ,docstring
     (let* ,bindings
       ,body)))

(make-fn my-fn
  "This is my function."
  :bindings ((one 1)
             (two 2))
  :body (list one two))

Destructuring   destructuring

Editing   editing

Tools   tools

beginend.el   navigation

This package, by Damien Cassou and Matus Goljer, helps navigation by redefining the M-< and M-> keys do, depending on the major-mode.

iedit: Edit multiple regions simultaneously in a buffer or a region   refactoring

iedit makes it easy to rename symbols within a function or in a whole buffer. Simply activate iedit-mode with point on a symbol, and it will be highlighted in the chosen scope, and any changes you make to the symbol are made in each highlighted occurrence. It's like a smart, purposeful version of multiple-cursors.

The editor of this handbook uses iedit with these customizations:

ap/iedit-or-flyspell
Globally bound to C-;. In a prog-mode-derived buffer, either corrects the last misspelled word with flyspell when point is in a comment or string, or activates iedit-mode. In non- prog-mode-derived buffers, corrects with flyspell.
(defun ap/iedit-or-flyspell ()
  "Call `iedit-mode' or correct misspelling with flyspell, depending..."
  (interactive)
  (if (or iedit-mode
          (and (derived-mode-p 'prog-mode)
               (not (or (nth 4 (syntax-ppss))
                        (nth 3 (syntax-ppss))))))
      ;; prog-mode is active and point is in a comment, string, or
      ;; already in iedit-mode
      (call-interactively #'ap/iedit-mode)
    ;; Not prog-mode or not in comment or string
    (if (not (equal flyspell-previous-command this-command))
        ;; FIXME: This mostly works, but if there are two words on the
        ;; same line that are misspelled, it doesn't work quite right
        ;; when correcting the earlier word after correcting the later
        ;; one

        ;; First correction; autocorrect
        (call-interactively 'flyspell-auto-correct-previous-word)
      ;; First correction was not wanted; use popup to choose
      (progn
        (save-excursion
          (undo)) ; This doesn't move point, which I think may be the problem.
        (flyspell-region (line-beginning-position) (line-end-position))
        (call-interactively 'flyspell-correct-previous-word-generic)))))
ap/iedit-mode
Calls iedit-mode with function-local scope by default, or global scope when called with a universal prefix.
(defun ap/iedit-mode (orig-fn)
  "Call `iedit-mode' with function-local scope by default, or global scope if called with a universal prefix."
  (interactive)
  (pcase current-prefix-arg
    ('nil (funcall orig-fn '(0)))
    ('(4) (funcall orig-fn))
    (_ (user-error "`ap/iedit-mode' called with prefix: %s" prefix))))

;; Override default `iedit-mode' function with advice.
(advice-add #'iedit-mode :around #'ap/iedit-mode)
Helpful minibuffer message
Confirms when an iedit session has started.
(advice-add 'iedit-mode :after (lambda (&optional ignore)
                                 (when iedit-mode
                                   (minibuffer-message "iedit session started. Press C-; to end."))))
lispy: short and sweet LISP editing   elisp navigation parentheses
multiple-cursors.el: Multiple cursors   selection editing

Functions   functions

Including anonymous functions (lambdas).

Articles

What's in an Emacs Lambda « null program   lambdas byte_compilation lexical_binding scope

General   general

Libraries   libraries

Common Lisp Extensions (cl-lib)   built_in

This is the built-in cl-lib package which implements Common Lisp functions and control structures for Emacs Lisp.

dash.el   dash

Dash is a powerful general-purpose library that provides many useful functions and macros.

subr-x   built_in strings flow_control

Less commonly used functions that complement basic APIs, often implemented in C code (like hash-tables and strings), and are not eligible for inclusion in subr.el.

This is a built-in package that provides several useful functions and macros, such as thread-first / last, if-let / when-let, hash-table functions, and string functions. It's easy to forget about this, since:

Do not document these functions in the lispref. http://lists.gnu.org/archive/html/emacs-devel/2014-01/msg01006.html

Tools   tools

chemacs: Emacs profile switcher   testing

This package may be especially helpful for developing in one's own environment and testing in another, like default Emacs, Spacemacs, etc.

Chemacs is an Emacs profile switcher, it makes it easy to run multiple Emacs configurations side by side. Think of it as a bootloader for Emacs.

Emacs configuration is either kept in a ~/.emacs file or, more commonly, in a ~/.emacs.d directory. These paths are hard-coded. If you want to try out someone else’s configuration, or run different distributions like Prelude or Spacemacs, then you either need to swap out ~/.emacs.d, or run Emacs with a different $HOME directory set. This last approach is quite common, but has some real drawbacks, since now packages will no longer know where your actual home directory is.

All of these makes trying out different Emacs configurations and distributions needlessly cumbersome. Various approaches to solving this have been floated over the years. There’s an Emacs patch around that adds an extra command line option, and various examples of how to add a command line option in userspace from Emacs Lisp.

Chemacs tries to implement this idea in a user-friendly way, taking care of the various edge cases and use cases that come up.

Multiprocessing (generators, threads)   multiprocessing

Articles   articles

Emacs 26 Brings Generators and Threads « null program   threads generators byte_compilation closures iterators

Chris Wellons explains the new generators and threads that Emacs 26 provides. He also shows an example of writing a cl-case form that uses the new switch jump table opcode in Emacs 26.

Packaging   packaging

Best practices   best_practices

Autoloads   autoloads
TODO Autoloading macro-generated functions

This may actually be a bug, or at least an unanswered question.

How to use autoload cookies for custom defun-like macros? : emacs:

Say I have a macro deffoo that expands to some custom kind of defun, and I want to use an autoload cookie to autoload the result. According to the manual,

;;;###autoload (deffoo bar   ...)

copies the entire form to autoloads.el, and something like

;;;###autoload (autoload 'bar "this-file") (deffoo bar   ...)

should be used instead. What confuses me is this StackOverflow comment by who appears to be Stefan Monnier, saying that Emacs should expand the macro before generating the autoload, and that it's probably a bug when this does not happen.

Can anyone clear up what the intended behaviour is?

[2018-01-15 Mon 03:37] The correct way to do this is documented in this bug report.

Integration with other packages
Optional support

Sometimes you want your package to integrate with other packages, but you don't want to require users to install those other packages. For example, you might want your package to work with Helm, Ivy, or the built-in Emacs completing-read, but you don't want to declare a dependency on and require Helm or Ivy, which would force users to install them to use your package.

The best way to handle this is with the with-eval-after-load macro. The Emacs manual has a page on it, and this StackOverflow question has some more info. You can also see an example, which also uses declare-function to prevent byte-compiler errors.

Lexical binding   lexical_binding built_in

You should always use lexical binding by setting the header in the first line of the file:

;;; filename.el --- File description  -*- lexical-binding: t; -*-
Template

When you make a new package, the auto-insert command will insert a set of standard package headers for you. However, here is a more comprehensive template you can use:

;;; package-name.el --- Package description (don't include the word "Emacs")  -*- lexical-binding: t; -*-

;; Copyright (C) 2017 First Last

;; Author: First Last <name@example.com>
;; URL: http://example.com/package-name.el
;; Version: 0.1-pre
;; Package-Requires: ((emacs "25.2"))
;; Keywords: something

;; This file is not part of GNU Emacs.

;;; Commentary:

;; This is my package.  It is nice.  You should try it.

;;;; Installation

;;;;; MELPA

;; If you installed from MELPA, you're done.

;;;;; Manual

;; Install these required packages:

;; + foo
;; + bar

;; Then put this file in your load-path, and put this in your init
;; file:

;; (require 'package-name)

;;;; Usage

;; Run one of these commands:

;; `package-name-command': Frobnicate the flange.

;;;; Tips

;; + You can customize settings in the `package-name' group.

;;;; Credits

;; This package would not have been possible without the following
;; packages: foo[1], which showed me how to bifurcate, and bar[2],
;; which takes care of flanges.
;;
;;  [1] https://example.com/foo.el
;;  [2] https://example.com/bar.el

;;; License:

;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with this program.  If not, see <http://www.gnu.org/licenses/>.

;;; Code:

;;;; Requirements

(require 'foo)
(require 'bar)

;;;; Customization

(defgroup package-name nil
  "Settings for `package-name'."
  :link '(url-link "http://example.com/package-name.el"))

(defcustom package-name-something nil
  "This setting does something."
  :type 'something)

;;;; Variables

(defvar package-name-var nil
  "A variable.")

;;;;; Keymaps

;; This technique makes it easier and less verbose to define keymaps.

(defvar package-name-map
  ;; This makes it easy and much less verbose to define keys
  (let ((map (make-sparse-keymap "package-name map"))
        (maps (list
               ;; Mappings go here, e.g.:
               "RET" #'package-name-RET-command
               [remap search-forward] #'package-name-search-forward
               )))
    (cl-loop for (key fn) on maps by #'cddr
             do (progn
                  (when (stringp key)
                    (setq key (kbd key)))
                  (define-key map key fn)))
    map))

;;;; Functions

;;;;; Commands

;;;###autoload
(defun package-name-command (args)
  "Frobnicate the flange."
  (interactive)
  (package-name--something)
  (bar))

;;;;; Support

(defun package-name--something (args)
  "This function helps frobnicate the flange."
  (foo))

;;;; Footer

(provide 'package-name)

;;; package-name.el ends here
Readme

You should always include a readme with your project. Typically it will be include most of the commentary section. Here's a template that goes with the package template above:

#+PROPERTY: LOGGING nil

# Note: This readme works with the org-make-toc <https://github.com/alphapapa/org-make-toc> package, which automatically updates the table of contents.

* package-name
:PROPERTIES:
:TOC:      ignore
:END:

file:https://melpa.org/packages/package-name-badge.svg file:https://stable.melpa.org/packages/package-name-badge.svg

This is my package.  It is nice.  You should try it.

** Screenshots

This screenshot shows how to frobnicate the fripulator:

screenshot1.png

* Contents                                                         :noexport:
:PROPERTIES:
:TOC:      this
:END:
  -  Installation
  -  Usage
  -  Changelog
  -  Credits
  -  Development
  -  License

* Installation
:PROPERTIES:
:TOC:      0
:END:

** MELPA

If you installed from MELPA, you're done.  Just run one of the commands below.

** Manual

  Install these required packages:

  + foo
  + bar

  Then put this file in your load-path, and put this in your init file:

  #+BEGIN_SRC elisp
(require 'package-name)
  #+END_SRC

* Usage
:PROPERTIES:
:TOC:      0
:END:

  Run one of these commands:

  + package-name-command: Frobnicate the flange.

** Tips

+ You can customize settings in the package-name group.

* Changelog
:PROPERTIES:
:TOC:      0
:END:

** 1.1.0

Additions
+  Add command package-name-debarnacle to de-barnacle the hull.

Changes
+ Command package-name-anchor now takes an argument, weigh or let-go.

Internal
+  Rewrote input parsing.
+  Factored out anchor-weighing.

** 1.0.1

Fixes
+  Ensure anchor is secure before returning from package-name-anchor.

** 1.0.0

Initial release.

* Credits

  This package would not have been possible without the following packages: foo which showed me how to bifurcate, and bar, which takes care of flanges.

* Development

Bug reports, feature requests, suggestions — oh my!

* License

GPLv3

# Local Variables:
# eval: (require 'org-make-toc)
# before-save-hook: org-make-toc
# org-export-with-properties: ()
# org-export-with-title: t
# End:
Version numbers

Version numbers which are valid in Emacs are those accepted by the function version-to-list, which uses the variables version-separator and version-regexp-alist. See their documentation for specific, up-to-date information. version-to-list's documentation (as of Emacs 26.1) is reproduced here for convenience:

The version syntax is given by the following EBNF:

VERSION ::= NUMBER ( SEPARATOR NUMBER )*.

NUMBER ::= (0|1|2|3|4|5|6|7|8|9)+.

SEPARATOR ::= ‘version-separator’ (which see)
| ‘version-regexp-alist’ (which see).

The NUMBER part is optional if SEPARATOR is a match for an element
in ‘version-regexp-alist’.

Examples of valid version syntax:

1.0pre2 1.0.7.5 22.8beta3 0.9alpha1 6.9.30Beta 2.4.snapshot .5

Examples of invalid version syntax:

1.0prepre2 1.0..7.5 22.8X3 alpha3.2

Examples of version conversion:

Version String Version as a List of Integers
".5" (0 5)
"0.9 alpha" (0 9 -3)
"0.9AlphA1" (0 9 -3 1)
"0.9snapshot" (0 9 -4)
"1.0-git" (1 0 -4)
"1.0.7.5" (1 0 7 5)
"1.0.cvs" (1 0 -4)
"1.0PRE2" (1 0 -1 2)
"1.0pre2" (1 0 -1 2)
"22.8 Beta3" (22 8 -2 3)
"22.8beta3" (22 8 -2 3)

Reference   reference

Package headers and structure

The Emacs manual gives this example (I've added the lexical-binding part). Also see template.

;;; superfrobnicator.el --- Frobnicate and bifurcate flanges  -*- lexical-binding: t; -*-

;; Copyright (C) 2011 Free Software Foundation, Inc.

;; Author: J. R. Hacker <jrh@example.com>
;; Version: 1.3
;; Package-Requires: ((flange "1.0"))
;; Keywords: multimedia, frobnicate
;; URL: http://example.com/jrhacker/superfrobnicate

...

;;; Commentary:

;; This package provides a minor mode to frobnicate and/or
;; bifurcate any flanges you desire. To activate it, just type
...

;;;###autoload
(define-minor-mode superfrobnicator-mode
...

Pattern matching   destructuring pattern_matching

Articles   articles

Pattern Matching in Emacs Lisp – Wilfred Hughes::Blog   pcase shadchen cl dash

Pattern matching is invaluable in elisp. Lists are ubiquitous, and a small amount of pattern matching can often replace a ton of verbose list fiddling.

Since this is Lisp, we have lots of choices! In this post, we'll compare cl.el, pcase.el, dash.el, and shadchen, so you can choose the best fit for your project. We'll look at the most common use cases, and end with some recommendations.

For the sake of this post, we'll consider both pattern matching and destructuring, as they're closely related concepts.

A callable plist data structure for Emacs   plists macros

John Kitchin demonstrates some macros that make it easy to access plist values.

Libraries   libraries

dash.el   dash

Dash is a powerful library, and one of its features is powerful destructuring with its -let macro, and several others that work the same way.

pcase   built_in pcase

pcase is built-in to Emacs. Its syntax can be confusing, but it is very powerful.

Articles   articles
EmacsWiki: Pattern Matching   examples EmacsWiki

There are lots of examples here.

Examples   examples
TODO dash

[2018-07-27 Fri 23:29] Dash has new abilities, including -setq, and destructuring plists with implied variable names (i.e. just the keys can be specified, reducing repetition).

pcase-let   destructuring

This example shows the use of pcase-let* to destructure and bind a nested alist:

(let ((alphabets (a-list 'English (a-list 'first "a"
                                          'second "b")
                         'Greek (a-list 'first "α"
                                        'second "β"))))
  (pcase-let* (((map English) alphabets)
               ((map ('first letter) second) English))
    (list letter second)))  ;; => ("a" "b")
shadchen-el   shadchen el

A powerful, Racket-style pattern-matching library.

Tools   tools

let-alist   alists macros destructuring

let-alist is the best thing to happen to associative lists since the invention of the cons cell. This little macro lets you easily access the contents of an alist, concisely and efficiently, without having to specify them preemptively. It comes built-in with 25.1, and is also available on GNU Elpa for older Emacsen.

Example:

(defun sx-question-list--print-info (question-data)
  "DOC"
  (let-alist question-data
    (list
     question-data
     (vector
      (int-to-string .score)
      (int-to-string .answer_count)
      .title " "
      .owner.display_name
      .last_activity_date sx-question-list-ago-string
      " " .tags))))
Articles   articles
New on Elpa and in Emacs 25.1: let-alist · Endless Parentheses

Here Artur introduces the macro and gives examples.

with-dict, with-plist-vals   macros plists

Courtesy of John Kitchin:1

(defmacro with-dict (key-vals &rest body)
  "A context-manager for a plist where each key is a callable
function that returns the value."
  (declare (indent 1))
  (let* ((g (if (symbolp key-vals)
                (symbol-value key-vals)
              key-vals))
         (keys (-slice g 0 nil 2)))
    `(labels ,(loop for key in keys
                    collect
                    (list key '() `(plist-get ',g ,key)))
       ,@body)))

;; Used as:

(with-dict (:a 1 :b 'some-symbol :c 3)
           (:b))

(let ((d '(:key1 1 :key2 some-other-symbol :key3 3)))
  (with-dict d
             (format "We got %s" (:key2))))

And:

(defmacro with-plist-vals (plist &rest body)
  "Bind the values of a plist to variables with the name of the keys."
  (declare (indent 1))
  `(let ,(loop for key in (-slice plist 0 nil 2)
               for val in (-slice plist 1 nil 2)
               collect (list (intern
                              (substring (symbol-name key) 1))
                             val))
     ,@body))

;; Used like:

(with-plist-vals (:a 4 :b 6)
                 (* 2 a))

Profiling / Optimization   profiling optimization

Articles   articles

How to Write Fast(er) Emacs Lisp « null program

Chris Wellons explains five ways to write faster Emacs Lisp code.

Macros   macros

bench

From Phil Lord's m-buffer-el:

(cl-defmacro bench (&optional (times 100000) &rest body)
  "Call `benchmark-run-compiled' on BODY with TIMES iterations, returning list suitable for Org source block evaluation.
Garbage is collected before calling `benchmark-run-compiled' to
avoid counting existing garbage which needs collection."
  (declare (indent defun))
  `(progn
     (garbage-collect)
     (list '("Total runtime" "# of GCs" "Total GC runtime")
           'hline
           (benchmark-run-compiled ,times
             (progn
               ,@body)))))

Used like this:

(bench 1000000
  (cons 'time (current-time)))

When called from an Org source block, it gives output like this:

Total runtime # of GCs Total GC runtime
1.657838266 3 1.4723854609999876
bench-multi

This macro makes comparing multiple forms easy:

(cl-defmacro bench-multi (&key (times 1) forms ensure-equal)
  "Run FORMS with `benchmark-run-compiled' for TIMES iterations, returning list suitable for Org source block evaluation.

When ENSURE-EQUAL is non-nil, compare the results of FORMS and
ensure they are `equal'.  If they aren't, raise an error, and if
the results are sequences, show the difference between them using
`seq-difference'.

If the first element of a form is a string, the string is used as
the form's description in the results; otherwise, forms are
numbered from 0.

Before `benchmark-run-compiled' is called for each form,
`garbage-collect' is called."
  (declare (indent defun))
  (let ((results (gensym))
        (result-times (gensym))
        (header '(("Form" "x faster than next" "Total runtime" "# of GCs" "Total GC runtime")
                  hline))
        (descriptions (cl-loop for form in forms
                               for i from 0
                               collect (if (stringp (car form))
                                           (prog1 (car form)
                                             (setf (nth i forms) (cadr (nth i forms))))
                                         i))))
    `(let* ((,results (make-hash-table))
            (,result-times (sort (list ,@(cl-loop for form in forms
                                                  for i from 0
                                                  for description = (nth i descriptions)
                                                  collect `(progn
                                                             (garbage-collect)
                                                             (cons ,description
                                                                   (benchmark-run-compiled ,times
                                                                     ,(if ensure-equal
                                                                          `(puthash ,description ,form ,results)
                                                                        form))))))
                                 (lambda (a b)
                                   (< (second a) (second b))))))
       ,(when ensure-equal
          `(cl-loop with keys = (hash-table-keys ,results)
                    for i from 0 to (- (length keys) 2)
                    unless (equal (gethash (nth i keys) ,results)
                                  (gethash (nth (1+ i) keys) ,results))
                    do (if (sequencep (gethash (car (hash-table-keys ,results)) ,results))
                           (let* ((k1) (k2)
                                  ;; If the difference in one order is nil, try in other order.
                                  (difference (or (setq k1 (nth i keys)
                                                        k2 (nth (1+ i) keys)
                                                        difference (seq-difference (gethash k1 ,results)
                                                                                   (gethash k2 ,results)))
                                                  (setq k1 (nth (1+ i) keys)
                                                        k2 (nth i keys)
                                                        difference (seq-difference (gethash k1 ,results)
                                                                                   (gethash k2 ,results))))))
                             (user-error "Forms' results not equal: difference (%s - %s): %S"
                                         k1 k2 difference))
                         ;; Not a sequence
                         (user-error "Forms' results not equal: %s:%S  %s:%S"
                                     (nth i keys) (nth (1+ i) keys)
                                     (gethash (nth i keys) ,results)
                                     (gethash (nth (1+ i) keys) ,results)))))
       ;; Add factors to times and return table
       (append ',header
               (cl-loop with length = (length ,result-times)
                        for i from 0 to (1- length)
                        for time = (second (nth i ,result-times))
                        for description = (car (nth i ,result-times))
                        for factor = (if (< i (1- length))
                                         (format "%.2f" (/ (second (nth (1+ i) ,result-times))
                                                           (second (nth i ,result-times))))
                                       "slowest")
                        collect (append (list description factor)
                                        (cdr (nth i ,result-times))))))))

Used like:

(bench-multi
  :forms (("org-map-entries" (sort (org-map-entries (lambda ()
                                                      (nth 4 (org-heading-components)))
                                                    "/+MAYBE" 'agenda)
                                   #'string<))
          ("regexp" (sort (-flatten
                           (-non-nil
                            (mapcar (lambda (file)
                                      (let ((case-fold-search t))
                                        (with-current-buffer (find-buffer-visiting file)
                                          (org-with-wide-buffer
                                           (goto-char (point-min))
                                           (cl-loop with regexp = (format org-heading-keyword-regexp-format "MAYBE")
                                                    while (re-search-forward regexp nil t)
                                                    collect (nth 4 (org-heading-components)))))))
                                    (org-agenda-files))))
                          #'string<))))
Form x faster than next Total runtime # of GCs Total GC runtime
regexp 62.50 0.043138672 0 0.0
org-map-entries slowest 2.69609941 0 0.0

It can also help catch bugs by ensuring that each form returns the same results. For example, the benchmark above contains a subtle bug: because case-fold-search in the regexp form is non-nil, the regexp is compared case-insensitively, so it matches Org headings which start with Maybe rather than only ones which start with MAYBE. Using the :ensure-equal t argument to bench-multi compares the results and raises an error showing the difference between the two sequences the forms evaluate to:

(bench-multi
  :ensure-equal t
  :forms (("org-map-entries" (sort (org-map-entries (lambda ()
                                                      (nth 4 (org-heading-components)))
                                                    "/+MAYBE" 'agenda)
                                   #'string<))
          ("regexp" (sort (-flatten
                           (-non-nil
                            (mapcar (lambda (file)
                                      (let ((case-fold-search t))
                                        (with-current-buffer (find-buffer-visiting file)
                                          (org-with-wide-buffer
                                           (goto-char (point-min))
                                           (cl-loop with regexp = (format org-heading-keyword-regexp-format "MAYBE")
                                                    while (re-search-forward regexp nil t)
                                                    collect (nth 4 (org-heading-components)))))))
                                    (org-agenda-files))))
                          #'string<))))
user-error: Forms’ results not equal: difference (regexp - org-map-entries): ("Maybe this is not the case?")

Fixing the error, by setting case-fold-search to nil, not only makes the forms give the same result but, in this case, doubles the performance of the faster form:

(bench-multi
  :ensure-equal t
  :forms (("org-map-entries" (sort (org-map-entries (lambda ()
                                                      (nth 4 (org-heading-components)))
                                                    "/+MAYBE" 'agenda)
                                   #'string<))
          ("regexp" (sort (-flatten
                           (-non-nil
                            (mapcar (lambda (file)
                                      (let ((case-fold-search nil))
                                        (with-current-buffer (find-buffer-visiting file)
                                          (org-with-wide-buffer
                                           (goto-char (point-min))
                                           (cl-loop with regexp = (format org-heading-keyword-regexp-format "MAYBE")
                                                    while (re-search-forward regexp nil t)
                                                    collect (nth 4 (org-heading-components)))))))
                                    (org-agenda-files))))
                          #'string<))))
Form x faster than next Total runtime # of GCs Total GC runtime
regexp 125.70 0.021080791 0 0.0
org-map-entries slowest 2.649818971 0 0.0

So this macro showed which code is faster and helped catch a subtle bug.

elp-profile

Call this macro from an Org source block and you'll get a results block showing which 20 functions were called the most times, how long they took to run, etc. prefixes should be a list of symbols matching the prefixes of the functions you want to instrument.

(defmacro elp-profile (times prefixes &rest body)
  (declare (indent defun))
  `(let (output)
     (dolist (prefix ,prefixes)
       (elp-instrument-package (symbol-name prefix)))
     (dotimes (x ,times)
       ,@body)
     (elp-results)
     (elp-restore-all)
     (point-min)
     (forward-line 20)
     (delete-region (point) (point-max))
     (setq output (buffer-substring-no-properties (point-min) (point-max)))
     (kill-buffer)
     (delete-window)
     (let ((rows (s-lines output)))
       (append (list (list "Function" "Times called" "Total time" "Average time")
                     'hline)
               (cl-loop for row in rows
                        collect (s-split (rx (1+ space)) row 'omit-nulls))))))

;; Use like this:
(elp-profile 10 '(map search goto-char car append)
  (goto-char (point-min))
  (search-forward "something"))

This gives a table like:

Function Times called Total time Average time
mapcar 30 0.0036004130 0.0001200137
search-forward 10 2.089…e-05 2.089…e-06
goto-char 10 6.926e-06 6.926e-07
car 13 3.956…e-06 3.043…e-07
append 1 5.96e-07 5.96e-07
mapatoms 1 0 0.0

Refactoring   refactoring

Regular expressions   regular_expressions

Articles   articles

Tools   tools

ample-regexps.el: Compose and reuse regular expressions with ease

ample-regexps complements the built-in rx macro by flexibly defining regular expressions with reusable parts. In the following example, the define-arx macro defines three things:

  • A macro url-rx, which expands to a regular expression string at compile time
  • A function url-rx-to-string, which can be used at runtime
  • A variable url-rx-constituents, containing form definitions to use
(define-arx url-rx
  '((http (seq bos (group "http") "://") )
    (https (seq bos (group "https") "://") )
    (https? (seq bos (group "http" (optional "s")) "://") )
    (protocol (seq bos (group (1+ (not (any ":")))) "://"))
    (host (group (1+ (not (any "/")))))
    (path (group "/" (1+ (not (any "?")))))
    (query (seq "?" (group (1+ (not (any "#"))))))
    (fragment (seq "#" (group (1+ anything))))))

The url-rx macro can then be used to test and select parts of URLs:

;; Accept HTTP or HTTPS
(let ((url "http://server/path?query#fragment"))
  (when (string-match (url-rx https? host path (optional query) (optional fragment)) url)
    (list (match-string 0 url)
          (match-string 1 url)
          (match-string 2 url)
          (match-string 3 url)
          (match-string 4 url)
          (match-string 5 url)))) ;=> ("http://server/path?query#fragment" "http" "server" "/path" "query" "fragment")

;; Only accept HTTPS, not plain HTTP
(let ((url "http://server/path?query#fragment"))
  (when (string-match (url-rx https host path (optional query) (optional fragment)) url)
    (list (match-string 0 url)))) ;=> nil

;; Accept any protocol, not just HTTP
(let ((url "ftp://server/path"))
  (when (string-match (url-rx protocol host path (optional query) (optional fragment)) url)
    (list (match-string 0 url)
          (match-string 1 url)
          (match-string 2 url)
          (match-string 3 url)
          (match-string 4 url)
          (match-string 5 url)))) ;=> ("ftp://server/path" "ftp" "server" "/path" nil nil)

This example shows the use of a function to expand a list of strings into a sequence:

(define-arx cond-assignment-rx
  '((alpha_ (regexp "[[:alpha:]_]"))
    (alnum_ (regexp "[[:alnum:]_]"))
    (ws (* blank))
    (sym (:func (lambda (_form &rest args)
                  `(seq symbol-start (or ,@args) symbol-end))))
    (cond-keyword (sym "if" "elif" "while"))
    (id (sym (+ alpha_) (* alnum_))))) ;; -> cond-assignment-rx

(cond-assignment-rx cond-keyword ws id ":" id ws "=" ws id) ;; -> "\\_<\\(?:elif\\|if\\|while\\)\\_>[[:blank:]]*\\_<\\(?:[[:alpha:]_]+\\|[[:alnum:]_]*\\)\\_>:\\_<\\(?:[[:alpha:]_]+\\|[[:alnum:]_]*\\)\\_>[[:blank:]]*=[[:blank:]]*\\_<\\(?:[[:alpha:]_]+\\|[[:alnum:]_]*\\)\\_>"

Strings   strings

Tools   tools

format$ macro   macros interpolation

The format$ macro (currently hosted here) allows for easy string interpolation, including optional % sequences as used by format. For example, this:

(format$ "Amount: ${amount% .02f} $name %s" date)

Expands to:

(format "Amount: % .02f %s %s" amount name date)

Since this happens at macro expansion time rather than at runtime, there is no performance penalty, in contrast to using s-lex-format.

Testing   testing

Libraries   libraries

Tools   tools

Emacs Lisp Regression Testing (ERT)   built_in

This is the standard, built-in Emacs testing library, used by core code and third-party packages alike.

emake.el: Test Elisp without the hoops

Test Elisp with services like Travis CI without the fuss of Cask – just you, your project, and (Emacs-)Make.

Things EMake does:

  • parses, installs, and runs tests for your package
  • provides all the power of Elisp to extend its capabilities on-demand

Things EMake will never do (or ‘reasons you may still need Cask’):

  • manage your development environment or provide tools to do so
  • provide ’bundler-like’ exec abilities (this includes Cask’s emacs and eval commands)

Version control   version_control

Packages   packages

Magit   git

One of the "killer apps" for Emacs–and for git!

XML / HTML   xml html

Libraries   libraries

esxml: An elisp library for working with xml, esxml and sxml

Probably the most featureful, usable library at the moment.

This library provides to formats for xml code generation. The primary form is esxml. esxml is the form that is returned by such functions as libxml-parse-xml-region and is used internally by emacs in many xml related libraries.

It also provides esxml-query:

;; Traditionally people pick one of the following options when faced
;; with the task of extracting data from XML in Emacs Lisp:
;;
;; - Using regular expressions on the unparsed document
;; - Manual tree traversal with `assoc', `car' and `cdr'
;;
;; Browsers faced a similar problem until jQuery happened, shortly
;; afterwards they started providing the `node.querySelector' and
;; `node.querySelectorAll' API for retrieving one or all nodes
;; matching a given CSS selector. This code implements the same API
;; with the `esxml-query' and `esxml-query-all' functions. The
;; following table summarizes the currently supported modifiers and
;; combinators:
;;
;; | Name                               | Supported? | Syntax      | 
;; |------------------------------------+------------+-------------|
;; | Namespaces                         | No         | foo|bar     | 
;; | Commas                             | Yes        | foo, bar    | 
;; | Descendant combinator              | Yes        | foo bar     | 
;; | Child combinator                   | Yes        | foo>bar     | 
;; | Adjacent sibling combinator        | No         | foo+bar     | 
;; | General sibling combinator         | No         | foo~bar     | 
;; | Universal selector                 | Yes        | *           | 
;; | Type selector                      | Yes        | tag         | 
;; | ID selector                        | Yes        | #foo        | 
;; | Class selector                     | Yes        | .foo        | 
;; | Attribute selector                 | Yes        | [foo]       | 
;; | Exact match attribute selector     | Yes        | [foo=bar]   | 
;; | Prefix match attribute selector    | Yes        | [foo^=bar]  | 
;; | Suffix match attribute selector    | Yes        | [foo$=bar]  | 
;; | Substring match attribute selector | Yes        | [foo*=bar]  | 
;; | Include match attribute selector   | Yes        | [foo~=bar]  | 
;; | Dash match attribute selector      | Yes        | [foo|=bar]  | 
;; | Attribute selector modifiers       | No         | [foo=bar i] | 
;; | Pseudo elements                    | No         | ::foo       | 
;; | Pseudo classes                     | No         | :foo        |

Example:

(defun org-books--amazon (url)
  "Return plist of data for book at Amazon URL."
  (cl-flet ((field (target-field list)
                   (cl-loop for li in list
                            for (field value) = (ignore-errors
                                                  (-let (((_ _ (_ _ field) value) li))
                                                    (list field value)))
                            when (equal field target-field)
                            return (s-trim value))))
    (let* ((html (org-web-tools--get-url url))
           (tree (with-temp-buffer
                   (insert html)
                   (libxml-parse-html-region (point-min) (point-max))))
           (author (esxml-query "span.author a.contributorNameID *" tree))
           (title (esxml-query "div#booksTitle h1#title > span *" tree))
           (details (esxml-query-all "table#productDetailsTable ul li" tree))
           (date (if-let ((printed (third (esxml-query-all "div#booksTitle h1#title span *" tree))))
                     ;; Printed book
                     (s-replace "– " "" printed)
                   ;; Kindle book
                   (field "Publication Date:" details)))
           (asin (field "ASIN:" details))
           (publisher (-some->> (field "Publisher:" details)
                                (replace-regexp-in-string (rx " (" (1+ anything) ")") "")))
           (isbn-10 (field "ISBN-10:" details))
           (isbn-13 (field "ISBN-13:" details)))
      (list :author author :title title :publisher publisher :date date
            :asin asin :isbn-10 isbn-10 :isbn-13 isbn-13))))
elquery: Read and manipulate HTML

It’s like jQuery, but way less useful.

Example:

<html style="height: 100vh">
  <head class="kek"><title class="kek" data-bar="foo">Complex HTML Page</title></head>
  <body class="kek bur" style="height: 100%">
    <h1 id="bar" class="kek wow">Wow this is an example</h1>
    <input id="quux" class="kek foo"/>
    <iframe id="baz" sandbox="allow-same-origin allow-scripts allow-popups allow-forms"
            width="100%" height="100%" src="example.org">
    </iframe>
  </body>
</html>
(let ((html (elq-read-file "~/kek.html")))
  (elq-el (car (elq-$ ".kek#quux" html))) ; => "input"
  (mapcar 'elq-el (elq-$ ".kek" html)) ; => ("input" "h1" "body" "title" "head")
  (mapcar (lambda (el) (elq-el (elq-parent el)))
          (elq-$ ".kek" html)) ; => ("body" "body" "html" "head" "html")
  (mapcar (lambda (el) (mapcar 'elq-el (elq-siblings el)))
          (elq-$ ".kek" html)) ; => (("h1" "input" "iframe") ("h1" "input" "iframe") ("head" "body") ("title") ("head" "body"))
  (elq-$ ".kek" html) ; => Hope you didn't like your messages buffer
  (elq-write html nil)) ; => "<html style=\"height: 100vh\"> ... </html>"
elfeed/xml-query.el

Provides lisp-based (rather than string-based) selectors. This library is primarily aimed at internal elfeed use rather than general use, however it may be useful to others. The author is considering publishing it separately.

;; Grab the top-level paragraph content from XHTML.
(xml-query-all '(html body p *) xhtml)

;; Extract all the links from an Atom feed.
(xml-query-all '(feed entry link [rel "alternate"] :href) xml)
enlive: query html document with css selectors

This provides a limited set of lisp-based selectors (rather than string-based selectors).

Example:

(require 'enlive)

(enlive-text
 (enlive-query (enlive-fetch "http://gnu.org/") [title])) ; => "The GNU Operating System and the Free Software Movement"
xml-plus: XML/HTML utilities

Mostly undocumented, providing three main functions:

;; Utility functions for xml parse trees.
;; - `xml+-query-all' and `xml+-query-first' are query functions that search
;; descendants in node lists. They don't work with namespace-aware parsing yet
;;
;; - `xml+-node-text' gets node text

Blogs   blogs

Planet Emacsen

This is the main community aggregator. You can find just about everyone's Emacs-related blog posts here.

Sacha Chua's Emacs News

This is Sacha's weekly Emacs news digest. Don't miss it!

Irreal

One of the top Emacs blogs, frequently updated, and often highlights other interesting blog entries in the community.

People   people

The Emacs community is so full of brilliant, generous people that I can't keep track of them all! I will surely overlook many, and I will add them in no particular order, but merely as I come across them again and again.

Artur Malabarba

Another prolific Emacs contributor, package developer, and blogger.

Damien Cassou

Packages

John Wiegley

John is the current Emacs maintainer.

Packages

Jonas Bernoulli

Jonas is a prolific Emacs package developer and maintainer. You could spend hours on his GitHub repo.

Packages

Matus Goljer

Packages

Oleh Krehel

Oleh is a prolific package author, having contributed many very high-quality packages. He also writes at his blog.

Roland Walker

Roland has published a wide variety of useful Emacs packages.

Sacha Chua

Sacha could easily be nominated the official Emacs ambassador, were there to be one. Her contributions to the Emacs and Org-mode communities are innumerable. One of her greatest recent contributions is her weekly Emacs news posts that serve as a digest of everything that happened in the Emacs world over the past week.

Wilfred Hughes

Wilfred has published several useful packages, and he's also leading the Rust Emacs port.

Contributions

Yes, please! Send pull requests and file issues on the GitHub repo. This is intended to be a community project.

Guidelines

Catalog and tag appropriately
New entries in the outline should have the appropriate tags and should follow the existing hierarchy. For example, articles should be tagged articles, and generally filed under an Articles heading using tag inheritance to apply the tag.
"Loosely" or "usefully" opinionated
Rather than being a place to dump links for users to sort out, we should do that ourselves. Links should have summaries and examples. Where there are multiple links to similar projects, we should compare them and guide users to what we think is generally the best solution, or the best solution for each use case.
Archive reference material
Much of the shared wisdom in the Emacs community is written in a variety of blogs by users and developers, as well as posts on Reddit, StackOverflow, etc. These tend to hang around for a long time, but being the Internet, this is never guaranteed. When linking to an article or other reference material, we should store a link to an archived version using this code.

Requirements

org-make-toc
This package updates the table of contents. It's automatically used by this document through file-local variables, which you should be prompted to allow when opening the file.

Tasks

These resources should be added to the appropriate sections above. Since it takes some work to catalog and organize them, they are dumped here for future reference. Pull requests for these are welcome!

TODO Articles to add [0/13]

TODO I wished GNU Emacs had… (2 min read)

TODO Reproduce bugs in emacs -Q (4 min read)

TODO Why package.el? (1 min read)

TODO Emacs script pitfalls (13 min read)

TODO Autoloads in Emacs Lisp (5 min read)

TODO Calling Python from Haskell (12 min read)

TODO Add tips for new developers

e.g.:

  • Commonly used minor modes
    • highlight-funcalls
    • highlight-quoted
    • outline-minor-mode

TODO Add Sean Allred

TODO Add Chris Wellons

TODO Vincent Toups' projects

He has a lot of interesting libraries on his repo, and some of them are extensively documented. An aspiring Emacs Lisp developer could learn a lot from his code.

TODO Add more of Roland Walker's packages

TODO Add MELPA

Mention @milkypostman, @purcell, @syohex, etc. Mention sandbox.

TODO Add Modern Emacs site

TODO Dynamic modules section

TODO GitHub - jkitchin/emacs-modules: Dynamic modules for emacs

TODO Add resources from its readme

For my own notes here are all the resources on dynamic modules I know of:

Here are the official Emacs header and example: emacs-module.h: http://git.savannah.gnu.org/cgit/emacs.git/tree/src/emacs-module.h?id=e18ee60b02d08b2f075903005798d3d6064dc013 modtest.c: http://git.savannah.gnu.org/cgit/emacs.git/tree/modules/mod-test/mod-test.c?id=e18ee60b02d08b2f075903005798d3d6064dc013

This simple example in C http://diobla.info/blog-archive/modules-tut.html

joymacs
http://nullprogram.com/blog/2016/11/05/
mruby
https://github.com/syohex/emacs-mruby-test
https://github.com/tromey/emacs-ffi
an actual ffi for emacs
elfuse
https://github.com/vkazanov/elfuse a file system in Emacs
asynchronous events
http://nullprogram.com/blog/2017/02/14/ related to elfuse
emacs-sqlite3
sqlite3 binding of Emacs Lisp
emacs-parson
JSON parser with dynamic module feature with parson
libyaml
libyaml
emacs-perl
Embed Perl into Emacs
https://github.com/syohex/emacs-eject
eject a cd
emacs-capstone
elisp bindings for the capstone disassembler
emacs-csound
EmacsLisp link to Csound's API via Emacs Modules
emacs-cmigemo
Emacs dynamic module for cmigemo
emacs-cipher
OpenSSL cipher binding of Emacs Lisp
emacs-lua
Lua engine from Emacs Lisp
emacs-ztd
libzstd binding of Emacs Lisp
mem-cached
libmemcached
https://coldnew.github.io/2d16cc25/
in Chinese, but with code

A collection of module resources: https://github.com/emacs-pe/emacs-modules

This may not be a dynamic module but claims an ffi haskell https://github.com/knupfer/haskell-emacs

TODO Test in MELPA sandbox

[2017-07-29 Sat 00:33] Not only should you test installing and using your package in the sandbox, but you should also test then exiting the sandbox Emacs, running it again with the package already installed, and loading it. This is because, when the sandbox installs the package, the byte-compilation seems to load some things that won't be loaded the same way when only loading the byte-compiled file (especially if you have any eval-when-compile lines, or unusual macros or things that modify the environment when loaded).

Code

This section contains code used to add to and update this document.

UNDERWAY Automate adding new links and summaries

TODO Get summary of page

DONE Get archive.is link for page

This bookmarklet should provide a way to get the URL:

javascript:void(open('https://archive.today/?run=1&url='+encodeURIComponent(document.location)))

Seems to only work if run in a browser, with JavaScript. But there's a Python package that has a shell command. So:

(require 's)

(defun emacs-package-dev-handbook--archiveis-capture (url)
  "Return archive.is archived URL for URL."
  (with-temp-buffer
    (when (zerop (call-process "archiveis" nil t nil url))
      (s-trim (buffer-string)))))

(cl-defun emacs-package-dev-handbook-insert-archiveis-property (url)
  "Set the \"archive.is\" property for entry at point to the archived version of URL.
Interactively, assumes heading on/before point is an Org link to
a web page."
  (interactive (list (save-excursion
                       (unless (org-at-heading-p)
                         (org-back-to-heading))
                       (beginning-of-line)
                       (when (re-search-forward org-bracket-link-regexp (line-end-position) 'noerror)
                         (org-link-unescape (match-string-no-properties 1))))))
  (when-let ((archive-url (emacs-package-dev-handbook--archiveis-capture url)))
    (org-set-property "archive.is" archive-url)))

TODO Insert new entry at point

Maybe use capture templates and refile?

Table of Contents

The ToC is generated using org-make-toc.

Config

I love Emacs and Org mode. This makes it so easy to make the document…alive! And automated! Beautiful.

Footnotes:

1
Copyright by John Kitchin, licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

Author: Adam Porter

Created: 2018-10-10 Wed 05:49

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