Lachlan O'Dea quelgar

Applied Functional Programming with Scala - Notes

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

Revisiting Tagless Final Interpreters

Tageless Final interpreters are an alternative to the traditional Algebraic Data Type (and generalized ADT) based implementation of the interpreter pattern. This document presents the Tageless Final approach with Scala, and shows how Dotty with it's recently added implicits functions makes the approach even more appealing. All examples are direct translations of their Haskell version presented in the Typed Tagless Final Interpreters: Lecture Notes (section 2).

The interpreter pattern has recently received a lot of attention in the Scala community. A lot of efforts have been invested in trying to address the biggest shortcomings of ADT/GADT based solutions: extensibility. One can first look at cats' Inject typeclass for an implementation of [Data Type à la Carte](http://www.cs.ru.nl/~W.Swierstra/Publications/DataTypesA

Programming as Theory Building

Peter Naur

Peter Naur's classic 1985 essay "Programming as Theory Building" argues that a program is not its source code. A program is a shared mental construct (he uses the word theory) that lives in the minds of the people who work on it. If you lose the people, you lose the program. The code is merely a written representation of the program, and it's lossy, so you can't reconstruct

	# Install QEMU OSX port with ARM support
	sudo port install qemu +target_arm
	export QEMU=$(which qemu-system-arm)

	# Dowload kernel and export location
	curl -OL \
	https://github.com/dhruvvyas90/qemu-rpi-kernel/blob/master/kernel-qemu-4.1.7-jessie
	export RPI_KERNEL=./kernel-qemu-4.1.7-jessie

	# Download filesystem and export location

	scala> import cats.implicits._
	import cats.implicits._

	scala> (1 -> 2) === (1 -> 3)
	res0: Boolean = true

	scala> import scala.reflect.runtime.universe._
	import scala.reflect.runtime.universe._

	scala> showCode(reify { (1 -> 2) === (1 -> 3) }.tree)

	package fpmax

	import scala.util.Try
	import scala.io.StdIn.readLine

	object App0 {
	def main: Unit = {
	println("What is your name?")

	val name = readLine()

	package spartan.training

	object TheMonadProblem {
	sealed trait Parser[+A] { self =>
	def map[B](f: A => B): Parser[B] = self.flatMap(a => Parser.succeed(f(a)))

	def flatMap[B](f: A => Parser[B]): Parser[B] = Parser.FlatMap(self, f)
	}
	object Parser {
	def succeed[A](a: A): Parser[A] = Succeed(a)