kevinmeredith

The Power of Referential Transparency

Acknowledgment

This post uses the excellent Ammonite REPL for Scala REPL.

Thank you, Li Haoyi, for building it!

About the Author

kevinmeredith

@ import $ivy.`org.typelevel::cats-effect:0.10.1` 
import $ivy.$                                  

@ import cats.effect.IO, cats.implicits._ 
import cats.effect.IO, cats.implicits._

@ val foo: IO[Either[String, Int]] = IO(throw new RuntimeException("!")) 
foo: IO[Either[String, Int]] = Delay(ammonite.$sess.cmd2$$$Lambda$2001/359985955@1bbfd42f)

@ foo.attempt 

kevinmeredith

(1) Creating an Engineering Career Ladder 

* he rolled out two career ladders in his experience
* he disputes that any company truly has a "flat org"
* notes that Senior Level Engineer is the anchor
* messaging is critical, e.g. important to announce promotions since it indicates importance of career ladder
* comments that general feedback, "you're doing great" isn't worth much. He suggests giving specific feedback on positives or needs-improvement
* Talked about 3 ladders: 
  - simple
  - snowflake

kevinmeredith

Thread Pools

Thread pools on the JVM should usually be divided into the following three categories:

1. CPU-bound
2. Blocking IO
3. Non-blocking IO polling

Each of these categories has a different optimal configuration and usage pattern.

kevinmeredith

@ val x: Kleisli[Task, String \/ Int, Boolean] = Kleisli {
    case -\/(_) => Task.now(true)
    case \/-(_) => Task.now(false)
  } 
x: Kleisli[Task, String \/ Int, Boolean] = Kleisli(ammonite.$sess.cmd5$$$Lambda$2811/243334301@38171f9)

@ val x: Kleisli[Task, String, Boolean] = Kleisli { _ => Task.now(true) } 
x: Kleisli[Task, String, Boolean] = Kleisli(ammonite.$sess.cmd6$$$Lambda$2832/1335778574@1bde703a)

kevinmeredith

@ import $ivy.`org.typelevel::cats-effect:0.10.1` 

@ import cats._, cats.data._, cats.implicits._, cats.effect._

@ def lift(i: Int): IO[Int] = Timer[IO].sleep(1.second) >> IO { 
  
     println(Thread.currentThread.getName + "At time = " + java.time.Instant.now)
     i
  } 

kevinmeredith

After scouring the internet and piece-mealing together the correct way to do this, here is a step-by-step, all-in-one-place guide to making logback STFU when running your unit tests.

Here's how to do it

Save the following as logback-test.xml under src/test/resources:

<configuration>
  <appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
    <encoder class="ch.qos.logback.classic.encoder.PatternLayoutEncoder">
      <pattern>%msg%n</pattern>

kevinmeredith

import $ivy.`com.beachape::enumeratum-circe:1.5.17`

import enumeratum._

sealed trait Color extends EnumEntry; case object Color extends Enum[Color] with CirceEnum[Color] {

  case object Red  extends Color
  case object Green extends Color
  case object Blue  extends Color

kevinmeredith

$cat app/Main.hs
module Main where

{-# LANGUAGE ExtendedDefaultRules #-}

import Control.Monad.Trans.List
import Conduit
import Control.Applicative

kevinmeredith

import Control.Arrow
import Control.Monad


-- Prelude Control.Monad Control.Arrow> :t (|||)
-- (|||) :: ArrowChoice a => a b d -> a c d -> a (Either b c) d

-- Prelude Control.Monad Control.Arrow> :k ArrowChoice
-- ArrowChoice :: (* -> * -> *) -> Constraint