jessitron

Letter to a Young Haskell Enthusiast, by Gershom Bazerman.

Condensed from: http://comonad.com/reader/2014/letter-to-a-young-haskell-enthusiast/

The following letter is about tendencies that come with the flush of excitement of learning any new thing. It is written specifically, because if we don't talk specifics, the generalities make no sense. It is a letter full of things I want to remember.

You’ve entered the world of strongly typed functional programming, and it is great. You want to share the great things you’ve learned, and you want to slay all the false statements in the world.

milessabin

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 }
  }

shajra

Basic Humanity

• Everyone is safe, respected, and treated with empathy and dignity.
• Pay is competitive, fair, and relatively transparent.
• Capitalize on a culture of looking at other jobs in other companies.

Organization

• Titled leaders deeply respect their implicit influence.
• Managers of technical workers are always highly technically skilled.

non

What is the appeal of dynamically-typed languages?

Kris Nuttycombe asks:

I genuinely wish I understood the appeal of unityped languages better. Can someone who really knows both well-typed and unityped explain?

I think the terms well-typed and unityped are a bit of question-begging here (you might as well say good-typed versus bad-typed), so instead I will say statically-typed and dynamically-typed.

I'm going to approach this article using Scala to stand-in for static typing and Python for dynamic typing. I feel like I am credibly proficient both languages: I don't currently write a lot of Python, but I still have affection for the language, and have probably written hundreds of thousands of lines of Python code over the years.

julienroubieu

import java.util.Optional

/**
 * Conversions between Scala Option and Java 8 Optional.
 */
object JavaOptionals {
  implicit def toRichOption[T](opt: Option[T]): RichOption[T] = new RichOption[T](opt)
  implicit def toRichOptional[T](optional: Optional[T]): RichOptional[T] = new RichOptional[T](optional)
}

tpolecat

EDIT: This gist has been promoted and is now a blog post.

Kinda-Curried Type Parameters

Scala methods can have multiple lists of value parameters but only one list of type parameters, which is occasionally irritating when some are inferable and others are not. Consider this method which has two type parameters, one inferable and one not.

import scalaz._, Scalaz._

raichoo

 {-# LANGUAGE NPlusKPatterns #-}
module Main where

import Test.QuickCheck

data NatF a
  = ZeroF
  | SuccF a

instance Functor NatF where

djspiewak

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

androidfred

Haskell, Stack and Intellij IDEA IDE setup tutorial how to get started

Upon completion you will have a sane, productive Haskell environment adhering to best practices.

Basics

• Haskell is a programming language.
• Stack is tool for Haskell projects. (similar tools for other languages include Maven, Gradle, npm, RubyGems etc)
• Intellij IDEA IDE is a popular IDE.

Install required libraries

sudo apt-get install libtinfo-dev libghc-zlib-dev libghc-zlib-bindings-dev

jdegoes

case class IO[A](unsafePerformIO: () => A) {
  def map[B](ab: A => B): IO[B] = IO(() => ab(unsafePerformIO()))
  def flatMap[B](afb: A => IO[B]): IO[B] =IO(() => afb(unsafePerformIO()).unsafePerformIO())
  def tryIO(ta: Throwable => A): IO[A] = 
    IO(() => IO.tryIO(unsafePerformIO()).unsafePerformIO() match {
      case Left(t) => ta(t)
      case Right(a) => a
    })
}
object IO {