Back to paredit

2021 August 14

Table of Contents

To simplify my s-exp workflow

I had been using lispy and lispyville for general s-expression editing and navigation previously. My setup works pretty well, but I often found the packages are a bit of a feature bloat. Plus, I don't use most of the transitive dependencies (ace-window, counsel, ivy, swiper, hydra). Over time, I started to realize what I like or want and what I don't care about for my workflow. I decided to switch to a lighter package to help me to build the workflow. So here we are, back to the good old paredit, again, for its simplicity.

Here's a list of features I actually want to use:

  1. S-exp navigation
  2. Killing s-exp
  3. Closing parentheses automatically
  4. Slurping and barfing s-exp
  5. Wrapping and unwrapping (or splicing) s-exp
  6. Dragging (or transposing) s-exp

Surprisingly, vanilla Emacs already supports half of the list! By default, C-M-(f|b|u|d|n|p) bounds to the s-exp navigation commands; C-M-k kills s-exp; C-M-t transposes s-exp that acts sort of like dragging s-exps. So I only need paredit to fill in the rest of the list.

To not-handle parentheses

I recently came across this reddit thread, which gave me a new perspective about handling parentheses for lispy languages. Actually, it's about how not handling parentheses. The constraint of keeping parentheses balanced all the time is surprisingly unnecessary and restrictive. Without this constraint, I started finding myself enjoying a lot more freedom in my REPL workflow. For example, when I have the Clojure code:

(-> data
    transform-1
    transform-2
    transform-3
    transform-4)

(let [a 1
      b 1
      c (+ a b)
      d (+ b c)
      e (+ c d)]
  ;; some more computation
  )

To inspect the transformation, I can temporarily insert unbalanced closing parentheses and code and then evaluate the code by putting the point at -!-:

(-> data
    transform-1
    transform-2)-!-  ; eval this s-exp
    transform-3
    transform-4)

(let [a 1
      b 1
      c (+ a b)] c)-!-  ; eval this s-exp
      d (+ b c)
      e (+ c d)]
  ;; some more computation
  )

Once I got the results, removing the temporary code is all it takes to have perfectly balanced parentheses again.

This is more or less the same as using cider-eval-sexp-up-to-point, but I don't want to memorize too many lesser-used keybindings. Plus, I prefer workflows that are more generic to other lispy languages.

To do this, I unbound a couple of commands from the paredit-mode-map, such as C-d and DEL. C-k is sometimes useful to delete code in bulk, so I still keep it bind to the paredit-kill command.

However, unlike what the reddit thread mentioned, I still find automatically inserting paren pairs helpful. This is probably because I work a lot in Clojure, which considers square brackets [] and curly braces {} as valid s-exp as well as parentheses (), so there are multiple ways to close an s-exp. Also, it's one less keystroke to type 😛.

This work is licensed under a Creative Commons Attribution 4.0 International License.