Ikhun Um ikhoon

Explaining Miles's Magic

Miles Sabin recently opened a pull request fixing the infamous SI-2712. First off, this is remarkable and, if merged, will make everyone's life enormously easier. This is a bug that a lot of people hit often without even realizing it, and they just assume that either they did something wrong or the compiler is broken in some weird way. It is especially common for users of scalaz or cats.

But that's not what I wanted to write about. What I want to write about is the exact semantics of Miles's fix, because it does impose some very specific assumptions about the way that type constructors work, and understanding those assumptions is the key to getting the most of it his fix.

For starters, here is the sort of thing that SI-2712 affects:

def foo[F[_], A](fa: F[A]): String = fa.toString

Monix Task: A diverging design

This document is about Task, an alternative for Scalaz's Task or Scala's Future. Note this is work in progress and this document suffered multiple modifications already:

API	Status Codes
[Twitter][tw]	200, 304, 400, 401, 403, 404, 406, 410, 420, 422, 429, 500, 502, 503, 504
[Stripe][stripe]	200, 400, 401, 402, 404, 429, 500, 502, 503, 504
[Github][gh]	200, 400, 422, 301, 302, 304, 307, 401, 403
[Pagerduty][pd]	200, 201, 204, 400, 401, 403, 404, 408, 500
[NewRelic Plugins][nr]	200, 400, 403, 404, 405, 413, 500, 502, 503, 503
[Etsy][etsy]	200, 201, 400, 403, 404, 500, 503
[Dropbox][db]	200, 400, 401, 403, 404, 405, 429, 503, 507

Collections Redesign Proposal

I'm going to start off by motivating what I'm doing here. And I want to be clear that I'm not "dissing" the existing collections implementation or anything as unproductively negative as that. It was a really good experiment, it was a huge step forward given what we knew back in 2.8, but now it's time to learn from that experiment and do better. This proposal uses what I believe are the lessons we can learn about what worked, what didn't work, and what is and isn't important about collections in Scala.

This is going to start out sounding really negative and pervasively dismissive, but bear with me! There's a point to all my ranting. I want to be really clear about my motivations for the proposal being the way that it is.

Problems

Generic Interfaces

Make Flashlight work on 10.10.4

Install SIMBL http://culater.net/software/SIMBL/SIMBL.php
Copy SpotlightSIMBL.bundle to /Library/Application Support/SIMBL/Plugins/ (a)
Copy Flashlight.osax to ~/Library/ScriptingAdditions/ (b)
Disable Flashlight
Enable Flashlight
Open Script Editor on your Mac (look for "Script Editor In Spotlight") and paste the following code (don't change Snow Leopard for Yosemite)

tell application "Spotlight" to inject SIMBL into Snow Leopard

	import shapeless._
	import ops.hlist.Tupler

	trait TupleGeneric[C <: Product] extends Serializable {
	type Repr <: Product

	def to(t : C) : Repr

	def from(r : Repr) : C
	}

	import shapeless._

	import scalaz._
	import Scalaz._

	object console extends App {

	trait Foo[A] {
	type B
	def value: B

	// An ADT+shapeless as a drop-in replacement for a standard Scala Enumeration.
	//
	// First the unsafe standard Scala Enumeration ...
	//
	object ScalaEnumDemo extends App {
	// Example from scala.Enumeration scaladoc. Terse ...
	object WeekDay extends Enumeration {
	type WeekDay = Value
	val Mon, Tue, Wed, Thu, Fri, Sat, Sun = Value
	}

	object Demo {
	// A couple of type classes with type members ...
	trait Foo[T] {
	type A
	}

	object Foo {
	implicit val fooIS = new Foo[Int] { type A = String }
	}

	{
	"presets": ["es2015"],
	"plugins": ["transform-runtime"]
	}