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System Design Cheatsheet

Picking the right architecture = Picking the right battles + Managing trade-offs

Basic Steps

1. Clarify and agree on the scope of the system

• User cases (description of sequences of events that, taken together, lead to a system doing something useful)
  • Who is going to use it?
  • How are they going to use it?

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(require '[clojure.core.match :refer [match]]
         '[clojure.string :as str]
         '[hiccup2.core :refer [html]]
         '[org.httpkit.server :as server])

(defn router [req]
  (let [paths (vec (rest (str/split (:uri req) #"/")))]
    (match [(:request-method req) paths]
           [:get ["users" id]] {:body (str (html [:div id]))}
           :else {:body (str (html [:html "Welcome!"]))})))

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require 'nokogiri'
require 'open-uri'

# Get a Nokogiri::HTML:Document for the page we're interested in...

doc = Nokogiri::HTML(open('http://www.google.com/search?q=tenderlove'))

# Do funky things with it using Nokogiri::XML::Node methods...

####

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Configuring Emacs for react, es6, and flow

For a while, JSX and new es6 syntax had flaky support in emacs, but there's been huge work on a lot of packages. Using emacs for JavaScript with React, ES6, and Flow (or Typescript, etc) is really easy and powerful in Emacs these days.

This is how you can work on modern web development projects with full support for tooling like JSX, Flow types, live eslint errors, automatic prettier.js formatting, and more.

Set up web-mode

web-mode provides most of the underlying functionality, so a huge shout-out to the maintainer(s) there.

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Installing Postgres via Brew (Read From below for issues)

Pre-Reqs

Brew Package Manager

In your command-line run the following commands:

1. brew doctor
2. brew update

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(assembly-load "ClojureClrEx")

(ns clync.core
  (:use [clojure.clr.pinvoke :only [dllimports]]))

(dllimports
 "Kernel32.dll"
 (GetStdHandle IntPtr [Int32])
 (SetConsoleTextAttribute Boolean [IntPtr UInt32]))

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using UnityEngine;

public class BoidBehaviour : MonoBehaviour
{
	void Update()
	{
		Boids.Core.update(transform);
	}
}

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Recent improvements to the ClojureScript compiler have greatly simplified setting up development versus production outputs.

This example uses Figwheel as something that you want to exclude for production, but the pattern is general.

With this simple setup you only need one html file/view and it will work for developement and production.

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Using JavaScript Libraries from ClojureScript

Using JavaScript libraries from ClojureScript involves two distinct concerns:

1. Packaging the code and delivering it to the browser
2. Making ClojureScript code that accesses JavaScript libraries safe for advanced optimization

Right now, the only single tool that solves these probems reliably, optimally, and with minimal configuration is shadow-cljs, and so that is what I favor. In paricular, shadow-cljs lets you install npm modules using npm or yarn and uses the resulting package.json to bundle external dependencies. Below I describe why, what alternatives there are, and what solutions I disfavor at this time.

Packaging and Delivering Code

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#include <iostream>
#include <cstdint>
#include <string>

#include "llvm/ExecutionEngine/JIT.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Module.h"
#include "llvm/PassManager.h"
#include "llvm/Support/TargetSelect.h"
#include "llvm/Analysis/Verifier.h"