viktorklang

/*
Copyright 2012-2021 Viktor Klang

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software

fljot

<!-- put this to IDEA keymaps config folder. For v13 it is <userdir>\.IntelliJIdea13\config\keymaps\ -->
<?xml version="1.0" encoding="UTF-8"?>
<keymap version="1" name="Mac OS X 10.5+ Windows Ctrl" parent="Mac OS X 10.5+">
  <action id="$Copy">
    <keyboard-shortcut first-keystroke="meta C" />
    <keyboard-shortcut first-keystroke="meta INSERT" />
    <keyboard-shortcut first-keystroke="control C" />
    <keyboard-shortcut first-keystroke="control INSERT" />
  </action>
  <action id="$Cut">

jdegoes

object test {
  import scalaz.zio._

  type UserID = String
  case class UserProfile(name: String)

  // The database module:
  trait Database {
    val database: Database.Service

btlines

import cats.{Id, Monad, Traverse, ~>}

import scala.concurrent.{Await, Future}
import scala.concurrent.duration.Duration

object TagLess extends App {

  case class PurchaseOrderId(value: String)
  case class ProductId(value: String)
  case class LocationId(value: String)

djspiewak

Getting Started in Scala

This is my attempt to give Scala newcomers a quick-and-easy rundown to the prerequisite steps they need to a) try Scala, and b) get a standard project up and running on their machine. I'm not going to talk about the language at all; there are plenty of better resources a google search away. This is just focused on the prerequisite tooling and machine setup. I will not be assuming you have any background in JVM languages. So if you're coming from Python, Ruby, JavaScript, Haskell, or anywhere…  I hope to present the information you need without assuming anything.

Disclaimer It has been over a decade since I was new to Scala, and when I was new to Scala, I was coming from a Java and Ruby background. This has probably caused me to unknowingly make some assumptions. Please feel free to call me out in comments/tweets!

One assumption I'm knowingly making is that you're on a Unix-like platform. Sorry, Windows users.

Getting the JVM

dragos

#!/bin/bash -e

# where Scala tarballs are extracted
SCALA_BASE=$HOME/scala

# Usage:
#
# Install:
# . /path/to/scala-env.sh in your bash profile
#

reactormonk

Symbol	Explanation	Hint
\/	Right-leaning Either	Split ways, go one way or the other
-\/	Left value of \/	- is on the left side
\/-	Right value of \/	- is on the right side
>>=	flatMap	shove result into
>>	flatMap(_ => ..)	shove into, but ignore the result
|@|	Applicatives into Tuple	Scream operator
|+|	Append via Monoid	+ was taken
`>	`	fa.map(_ => b)

djspiewak

Introduction to scalaz-stream

Every application ever written can be viewed as some sort of transformation on data. Data can come from different sources, such as a network or a file or user input or the Large Hadron Collider. It can come from many sources all at once to be merged and aggregated in interesting ways, and it can be produced into many different output sinks, such as a network or files or graphical user interfaces. You might produce your output all at once, as a big data dump at the end of the world (right before your program shuts down), or you might produce it more incrementally. Every application fits into this model.

The scalaz-stream project is an attempt to make it easy to construct, test and scale programs that fit within this model (which is to say, everything). It does this by providing an abstraction around a "stream" of data, which is really just this notion of some number of data being sequentially pulled out of some unspecified data source. On top of this abstraction, sca

djspiewak

Why not both?

With the recent announcement of cats-effect, a relevant question from the past resurfaces: why does IO, which is otherwise quite Task-like, not define both or race? To be clear, the type signatures of these functions would be as follows:

object IO {
  def both[A, B](ioa: IO[A], iob: IO[B])(implicit EC: ExecutionContext): IO[(A, B)] = ???
  def race[A, B](ioa: IO[A], iob: IO[B])(implicit EC: ExecutionContext): IO[Either[A, B]] = ???
}

pchiusano

/** GADTs in Scala and their limitations */

/** Background: what is an algebraic data type (ADT) ? 
  * ADT: (possibly) recursive datatype with sums and products
  * In scala - a trait with case classes (case class is product, subtyping is sum) 
  */

/** Motivation: untyped embedded DSL doesn't prevent nonsensical expressions */
sealed trait Expr { 
  def apply(other: Expr) = Ap(this, other)