#+TITLE:  Emacs Lisp Configuration
#+AUTHOR: Howard X. Abrams
#+DATE:   2022-05-11
#+FILETAGS: :emacs:

A literate programming file for configuring Emacs for Lisp programming.

#+BEGIN_SRC emacs-lisp :exports none
  ;;; ha-lisp --- configuring Emacs for Lisp programming. -*- lexical-binding: t; -*-
  ;;
  ;; © 2022 Howard X. Abrams
  ;;   This work is licensed under a Creative Commons Attribution 4.0 International License.
  ;;   See http://creativecommons.org/licenses/by/4.0/
  ;;
  ;; Author: Howard X. Abrams <http://gitlab.com/howardabrams>
  ;; Maintainer: Howard X. Abrams
  ;; Created: May 11, 2022
  ;;
  ;; This file is not part of GNU Emacs.
  ;;
  ;; *NB:* Do not edit this file. Instead, edit the original literate file at:
  ;;            /Users/howard.abrams/other/hamacs/ha-lisp.org
  ;;       And tangle the file to recreate this one.
  ;;
  ;;; Code:
  #+END_SRC
* Introduction
While I program in a lot of languages, I seem to be writing all my helper tools and scripts in … Emacs Lisp. So I’m cranking this up to 11.

New, /non-literal/ source code comes from [[file:templates/emacs-lisp-mode.el][emacs-lisp-mode template]]:
#+BEGIN_SRC emacs-lisp
  (ha-auto-insert-file (rx ".el" eol) "emacs-lisp-mode.el")
#+END_SRC
* Syntax Display
** Dim those Parenthesis
The [[https://github.com/tarsius/paren-face][paren-face]] project lowers the color level of parenthesis which I find better.

#+BEGIN_SRC emacs-lisp
  (use-package paren-face
    :hook (emacs-lisp-mode . paren-face-mode))
#+END_SRC
I'm going to play with the [[https://github.com/DogLooksGood/parinfer-mode][parinfer]] package.

* Navigation and Editing
** Clever Parenthesis
We need to make sure we keep the [[https://github.com/Fuco1/smartparens][smartparens]] project always in /strict mode/, because who wants to worry about paren-matching:
#+BEGIN_SRC emacs-lisp
  (use-package smartparens
    :custom
    (smartparens-global-strict-mode t)
    :hook
    (prog-mode . smartparens-strict-mode))
#+END_SRC

The [[https://github.com/luxbock/evil-cleverparens][evil-cleverparens]] solves having me create keybindings to the [[https://github.com/Fuco1/smartparens][smartparens]] project by updating the evil states with Lisp-specific bindings.
#+BEGIN_SRC emacs-lisp
  (use-package evil-cleverparens
    :after smartparens
    :custom
    (evil-cleverparens-use-additional-bindings t)
    (evil-cleverparens-use-additional-movement-keys t)
    (evil-cleverparens-use-s-and-S t)

    :init
    (require 'evil-cleverparens-text-objects)

    :hook
    (prog-mode . evil-cleverparens-mode))  ;; All the languages!
    ;; Otherwise: (emacs-lisp-mode . evil-cleverparens-mode)
#+END_SRC

The /trick/ to being effective with the [[https://www.emacswiki.org/emacs/ParEdit][paredit-family]] of extensions is learning the keys. The killer “app” is the slurp/barf sequence. Use the ~<~ key, in normal mode, to barf (or jettison)… in other words, /move/ the paren closer to the point. For instance:
#+BEGIN_SRC emacs-lisp
  (+ 41 (* ‖1 3))  ⟹  (+ 41 (* ‖1) 3)
#+END_SRC
Use the ~>~ key to /slurp/ in outside objects into the current expression… in other words, move the paren away from the point. For instance:
#+BEGIN_SRC emacs-lisp
  (+ 41 (* ‖1) 3)  ⟹  (+ 41 (* ‖1 3))
#+END_SRC

*Opening Parens.* Those two keys seem straight-forward, but they behave differently when the are on the opening parens.
When the point (symbolized by ~‖~) is /on/ the opening paren, ~<~ moves the paren to the left. For instance:
#+BEGIN_SRC emacs-lisp
  (+ 41 ‖(* 1 3))  ⟹  (+ ‖(41 * 1 3))
#+END_SRC
And  the ~>~ moves the paren to the right. For instance:
#+BEGIN_SRC emacs-lisp
  (+ 41 ‖(* 1 3))  ⟹ (+ 41 * ‖(1 3))
#+END_SRC

I would like to have a list of what keybindings that work in =normal= mode:
- ~M-h~ / ~M-l~ move back/forward by functions
- ~H~ / ~L~ move back/forward by s-expression
- ~M-i~ insert at the beginning of the form
- ~M-a~ appends at the end of the form
- ~M-o~ new form after the current sexp
- ~M-O~ new form /before/ the current sexp
- ~M-j~ / ~M-k~ drags /thing at point/ and back and forth in the form
- ~>~ slurp forward if at the end of form, at beginning, it barfs backwards
- ~<~ slurp backward if at start of form, at the end, it barfs forwards
- ~M-(~ / ~M-)~ wraps next/previous form in parens (braces and brackets work too)
- ~x~ unwraps if the point is on the =(= of an expression.
- ~D~ deletes an entire s-expression, but this can depend on the position of the point.

The other advantage is moving around by s-expressions. This takes a little getting used to, for instance:
- ~[~ and ~]~ move from paren to paren, essentially, from s-expression.
- ~H~ and ~L~ act similarly to the above.
- ~(~ and ~)~ move up to the parent s-expression

We need a real-world example. Let’s suppose we entered this:
#+BEGIN_SRC emacs-lisp
(format "The sum of %d %d is %d" a b (+ a b))
#+END_SRC
But we forgot to define the =a= and =b= variables. One approach, after Escaping into the normal state, is to hit ~(~ to just to the beginning of the s-expression, and then type,  ~M-(~ to wrap the expression, and type ~i~ to go into insert mode:
#+BEGIN_SRC emacs-lisp
  (‖ (format "The sum of %d %d is %d" a b (+ a b)))
#+END_SRC
And now we can enter the =let= expression.

Other nifty keybindings that I need to commit to muscle memory include:
| ~M-q~ | =sp-indent-defun=   |
| ~M-J~ | =sp-join-sexp=      |
| ~M-s~ | =sp-splice-sexp=    |
| ~M-S~ | =sp-split-sexp=     |
| ~M-t~ | =sp-transpose-sexp= |
| ~M-v~ | =sp-convolute-sexp= |
| ~M-r~ | =sp-raise-sexp=     |

** Eval Current Expression

A feature I enjoyed from Spacemacs is the ability to evaluate the s-expression currently containing the point. Not sure how how they made it, but cleverparens can help:

#+BEGIN_SRC emacs-lisp
(defun ha-eval-current-expression ()
  "Evaluates the expression the point is currently 'in'.
It does this, by jumping to the end of the current
expression (using evil-cleverparens), and evaluating what it
finds at that point."
  (interactive)
  (save-excursion
    (evil-cp-next-closing)
    (evil-cp-forward-sexp)
    (call-interactively 'eval-last-sexp)))
#+END_SRC

And we just need to bind it.
#+BEGIN_SRC emacs-lisp
  (ha-prog-leader
    "e c" '("current" . ha-eval-current-expression))
#+END_SRC
* Technical Artifacts                                :noexport:

Let's =provide= a name so we can =require= this file:

#+BEGIN_SRC emacs-lisp :exports none
  (provide 'ha-programming-elisp)
  ;;; ha-programming-elisp.el ends here
  #+END_SRC

#+DESCRIPTION: configuring Emacs for Lisp programming.

#+PROPERTY:    header-args:sh :tangle no
#+PROPERTY:    header-args:emacs-lisp  :tangle yes
#+PROPERTY:    header-args    :results none :eval no-export :comments no mkdirp yes

#+OPTIONS:     num:nil toc:nil todo:nil tasks:nil tags:nil date:nil
#+OPTIONS:     skip:nil author:nil email:nil creator:nil timestamp:nil
#+INFOJS_OPT:  view:nil toc:nil ltoc:t mouse:underline buttons:0 path:http://orgmode.org/org-info.js