Avaq

Algebraic Law Cheatsheet

An overview of algebraic laws from the perspective of a functional programmer. I've used a Haskell-esque syntax for the definitions of the laws and examples.

General Laws

name	definition	example
Identity [¹][]	f x = x	add 0 42 = 42

divs1210

Cut me some stack

(a deep dive into trampolines)

Divyansh Prakash, September 2023

Preface

sindresorhus

Pure ESM package

The package that linked you here is now pure ESM. It cannot be require()'d from CommonJS.

This means you have the following choices:

1. Use ESM yourself. (preferred)
   Use import foo from 'foo' instead of const foo = require('foo') to import the package. You also need to put "type": "module" in your package.json and more. Follow the below guide.
2. If the package is used in an async context, you could use await import(…) from CommonJS instead of require(…).
3. Stay on the existing version of the package until you can move to ESM.

bbqtd

Installing tmux-256color for macOS

• macOS 10.15.5
• tmux 3.1b

macOS has ncurses version 5.7 which does not ship the terminfo description for tmux. There're two ways that can help you to solve this problem.

The Fast Blazing Solution

Instead of tmux-256color, use screen-256color which comes with system. Place this command into ~/.tmux.conf or ~/.config/tmux/tmux.conf(for version 3.1 and later):

Avaq

const after = t => x => cont => {
  const id = setTimeout (cont, t, x)
  return () => clearTimeout (id)
}

const map = f => run => cont => run(x => cont (f (x)))
const chain = f => run => cont => run(x => f (x) (cont))

const run = chain (x => after (2000) (`${x}C`))
                  (map (x => `${x}B`)

Avaq

//
// utils
//

const thrush = x => f => f(x);

const indexBy = k => xs => xs.reduce((index, x) => {
  if(index[x[k]] != null) index[x[k]].push(x);
  else index[x[k]] = [x];
  return index;

safareli

var flatten = Function.prototype.apply.bind([].concat, [])
Array.prototype.chain = function(f) {
  return flatten(this.map(f))
}

var stepNext = function (x) { return {value: x, done: false }; };
var stepDone = function (x) { return {value: x, done: true }; };
Array.chainRec = function _chainRec(f, i) {
  var todo = [i];
  var res = [];

benperez

--dropWhereRepeated [1, 2, 2, 3, 3, 5, 7, 10]
--[1,5,7,10]
dropWhereRepeated :: (Eq a) => [a] -> [a]
dropWhereRepeated []  = []
dropWhereRepeated [x] = [x]
dropWhereRepeated (x : y : xs)
  | x == y    = dropWhereRepeated (dropWhile (== x) (xs))
  | otherwise = x : dropWhereRepeated (y : xs)

Avaq

I published a library which implements this idea; furry.

#	From	To	Normal	Alternative
1	a → b → c	a → c	f(_, b)(a)	f(_, b)(a)
2	a → b → c	b → a → c	nope	f(_)(b, a)
3	a → b → c → d	b → d	f(a, _, c)(b)	f(a, _, c)(b)
4	a → b → c → d	a → b → d	f(_, _, c)(a, b)	f(_, _, c)(a, b)
5	a → b → c → d	a → c → d	f(_, b)(a, c)	f(_, b, _)(a, c)

Avaq

const I  = x => x
const K  = x => y => x
const A  = f => x => f (x)
const T  = x => f => f (x)
const W  = f => x => f (x) (x)
const C  = f => y => x => f (x) (y)
const B  = f => g => x => f (g (x))
const S  = f => g => x => f (x) (g (x))
const S_ = f => g => x => f (g (x)) (x)
const S2 = f => g => h => x => f (g (x)) (h (x))