valadan

Latency numbers every programmer should know

L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns
L2 cache reference ........................... 7 ns
Mutex lock/unlock ........................... 25 ns
Main memory reference ...................... 100 ns             
Compress 1K bytes with Zippy ............. 3,000 ns  =   3 µs
Send 2K bytes over 1 Gbps network ....... 20,000 ns  =  20 µs
SSD random read ........................ 150,000 ns  = 150 µs

Read 1 MB sequentially from memory ..... 250,000 ns = 250 µs

valadan

import Pattern._
import Family._

def pattern[B](pf: PartialFunction[Name,B]) = new Extractor(pf.lift)

val Parents = new Extractor(parents.get)
val Children = new Extractor(children.get)

"Julie" match {
  case Parents(p) => "Julies parents are: " + p

valadan

def blockingAndVerbose: Profile = {
    val futureName = name()
    val futureScore = score()
    val futureFriends = Friends()

    val nameResult = Await.result(futureName, 10 seconds)
    val scoreResult = Await.result(futureScore, 10 seconds)
    val friendsResult = Await.result(futureFriends, 10 seconds)

    Profile(nameResult, scoreResult, friendsResult)

valadan

case class T() // your data type that you want to "implicitly" thread through

case class TReader[+A](run: T => A) {
  def map[B](f: A => B): TReader[B] =
    sys.error("VFJlYWRlcihmIGNvbXBvc2UgcnVuKQ==")

  def flatMap[B](f: A => TReader[B]): TReader[B] =
    sys.error("VFJlYWRlcih0ID0+IGYocnVuKHQpKSBydW4gdCk=")

  def &&&[B](x: TReader[B]): TReader[(A, B)] =

valadan

Category theory jargon cheat sheet

A primer/refresher on the category theory concepts that most commonly crop up in conversations about Scala or FP. (Because it's embarassing when I forget this stuff!)

I'll be assuming Scalaz imports in code samples, and some of the code may be pseudo-Scala.

Functor

A functor is something that supports map.

valadan

object merging {
  
 // Note: Tail-recursive stream functions should always be defined on objects, not traits.
 //       see http://stackoverflow.com/questions/12486762/scala-tail-recursive-stream-processor-function-defined-in-trait-holds-reference

 /**
   * Merges two ordered streams. The elements can be of different
   * types, but they need a mapping to a common type C.
   *
   * The mapped streams must be ordered ascending.

valadan

Advanced Functional Programming with Scala - Notes

Copyright © 2017 Fantasyland Institute of Learning. All rights reserved.

1. Mastering Functions

A function is a mapping from one set, called a domain, to another set, called the codomain. A function associates every element in the domain with exactly one element in the codomain. In Scala, both domain and codomain are types.

val square : Int => Int = x => x * x

valadan

Centralised logging for Docker containers running Spring Boot applications

Log flow through the system

About

We have a bunch of Spring Boot apps running in various Docker containers and wanted a centralised place to view the logs

valadan

keystore = "/etc/java-6-sun/security/cacerts"
keystore_pass = "foobar"

# you'll need foo.cert et. al. in files/default
certs = %w{foo bar bang}

certs.each do |cert|
  cookbook_file "#{Chef::Config[:file_cache_path]}/#{cert}.cert" do
    source "#{cert}.cert"
  end

valadan

Simple collection of Groovy scripts to help me maintain some Jenkins systems.

See also https://wiki.jenkins-ci.org/display/JENKINS/Jenkins+Script+Console