branneman

// Array = ordered + indexed + duplicate values
// a.k.a. List

const arr = [1, 2, 3]

// size
arr.length //=> 3

// random-access
arr[1] // 2

branneman

// FP Lenses
const lens = get => set => ({ get, set });
const view = lens => obj => lens.get(obj);
const set = lens => val => obj => lens.set(val)(obj);
const over = lens => fn => obj => set(lens)(fn(view(lens)(obj)))(obj);
const lensProp = key => lens(prop(key))(assoc(key));

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{
  // Tight coupling from A to B  => A needs B to be defined, callable and adhere to an interface
  // No coupling from B to A     => B does not need A in any way (pure fn)
  function a() {
    b()
  }
  function b() {}
}

{

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Primitive Types & Reference Types in JavaScript

An explanation of JavaScript's pass-by-value, which is unlike pass-by-reference from other languages.

Facts

• JavaScript has 2 kinds of variable types: primitive and reference.
• A fixed amount of memory is reserved after creation of every variable.
• When a variable is copied, it's in-memory value is copied.
• Passing a variable to a function via a call also creates a copy of that variable.

Primitive Types

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Better local require() paths for Node.js

Problem

When the directory structure of your Node.js application (not library!) has some depth, you end up with a lot of annoying relative paths in your require calls like:

const Article = require('../../../../app/models/article');

Those suck for maintenance and they're ugly.

Possible solutions

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// :: (String, String) => String
const spawn = require('child_process').spawnSync;

// :: String => [String]
const getRules = raw => raw
    .split('\n')
    .map(line => line.trim())
    .filter(line => !!line)
    .filter(line => line[0] !== '/' && line[0] !== '✖')
    .map(line => line.match(/[a-z-]+$/)[0]);

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def application(environ, start_response):
    import sys
    path = 'YOUR_WWW_ROOT_DIRECTORY'
    if path not in sys.path:
        sys.path.append(path)
    from pyinfo import pyinfo
    output = pyinfo()
    start_response('200 OK', [('Content-type', 'text/html')])
    return [output]

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// blob = file contents, identified by hash
const blobs = {
  '73d8a': 'import x from "y"; console.log("some file contents")',
  '9c6bd': 'D8 A1 31 0F ...',
  '547d4': '# Readme\nThis is documentation',
  'a0302': '# Readme\nThis is some updated documentation',
}
 
// tree = references to blobs and trees, identified by hash
const trees = {

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// Imperative: 'what' + 'how'
const makes1 = []
for (let i = 0; i < cars.length; i += 1) {
  makes1.push(cars[i].make)
}

// Declarative: only 'what'
const makes2 = cars.map((car) => car.make)

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// Producer
const range = (min, max, acc = []) => {
  if (max < min) throw new Error('not supported!')
  if (min >= max) return acc
  return range(min + 1, max, acc.concat(min))
}

// Consumer
const lt100 = range(0, 100)
//=> [1, 2, 3, 4, ..., 97, 98, 99]