Eric Torreborre etorreborre

Advanced 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

Configuring SBT to use 1Password

Install swig-python
Use pip to install 1pass
Install py-levenshtein to avoid annoying warnings
Locate the nearest 1pass script (note: it may be behind you)
Test 1pass on a random password

Create ~/.sbt/0.13/plugins/build.sbt with the following contents:

A Basic GADT Challenge

I have a bag of stuff.
My bag is awesome it can hold different types of things allocated by a name.
My bag is kind of ok, in that it can only hold certain types of things. Specifically it can hold Int's, String's and Bool's. But this also makes it convenient to access those things.
Conveniently the key tells me what type to expect.

In my haskell2010 world, I implement this as a simple data type:

	/**
	* In this version of `Traverse`, sequencing always goes through `List` (or some other canonical sequence type),
	* which can be done in a stack-safe manner using a balanced fold as in https://gist.github.com/pchiusano/7667597.
	* It's quite nice that `sequence` and `traverse` are now derived functions.
	*/
	trait Traverse[F[_]] extends Functor[F] {
	/** Inefficient but correct implementation of `toList` in terms of `mapAccumulate`. */
	def toList[A](f: F[A]): List[A] = mapAccumulate(f, List())((a, rbuf) => (a, a :: rbuf))._2.reverse

	/** The only function that must be implemented. Must be consistent with `map`. */

	origin https://github.com/gitbucket/gitbucket (fetch)
	origin https://github.com/gitbucket/gitbucket (push)

	Aug 08 18:50:38 Downloaded https://repo1.maven.org/maven2/com/sun/mail/javax.mail/1.5.2/javax.mail-1.5.2.jar
	Aug 08 18:50:38 Downloaded https://repo1.maven.org/maven2/com/typesafe/slick/slick_2.11/2.1.0/slick_2.11-2.1.0.jar
	Aug 08 18:50:38 [info] Fetched artifacts of io.github.gitbucket:gitbucket_2.11:4.3.0
	Aug 08 18:50:40 coursier.ResolutionException: 1 not found https://repo1.maven.org/maven2/org/apache/sshd/apache-sshd/1.2.0/apache-sshd-1.2.0.jar
	Aug 08 18:50:40 [error] (*:update) coursier.ResolutionException: 1 not found https://repo1.maven.org/maven2/org/apache/sshd/apache-sshd/1.2.0/apache-sshd-1.2.0.jar
	Aug 08 18:50:40 [error] Total time: 10 s, completed Aug 8, 2016 6:50:40 PM

	(* technically this is the lazy state monad. In particular, note the return type of get *)
	module type STATE_MONAD =
	sig
	type ('a,'s) st

	val return : 'a -> ('a,'s) st
	val bind : ('a,'s) st -> ('a -> ('b, 's) st) -> ('b, 's) st
	val get : ('s Lazy.t, 's) st
	val modify : ('s -> 's) -> (unit, 's) st
	val put : 's -> (unit, 's) st

	miles@frege:~$ ./shapeless.sh
	Loading...
	Welcome to the Ammonite Repl 0.5.2
	(Scala 2.11.7 Java 1.8.0_51)
	@ val l = 23 :: "foo" :: true :: HNil
	l: Int :: String :: Boolean :: HNil = ::(23, ::("foo", ::(true, HNil)))
	@

	#!/bin/bash
	test -e ~/.coursier/cr \|\| (mkdir -p ~/.coursier && wget -q -O ~/.coursier/cr https://git.io/vgvpD && chmod +x ~/.coursier/cr)
	CLASSPATH="$(~/.coursier/cr fetch -q -p \
	\
	com.typesafe.play:play-netty-server_2.11:2.5.0 \
	com.typesafe.play:play_2.11:2.5.0 \
	com.lihaoyi:ammonite-repl_2.11.7:0.5.2 \
	\
	)" java \
	-Dplay.crypto.secret=foo.bar.baz \

	package argonaut.example

	import argonaut._, Argonaut._
	import scalaz._, Scalaz._

	object UnionExample extends {

	sealed trait Thing
	final case class One(n: String, i: Int) extends Thing
	final case class Two(n: String) extends Thing

	{-# LANGUAGE NoMonomorphismRestriction #-}
	{-# LANGUAGE TemplateHaskell #-}
	{-# OPTIONS_GHC -fwarn-missing-methods #-}
	module Err where

	import Control.Lens
	import Control.Monad.Error
	import Control.Monad.Error.Lens

	-- Here is a fairly typical situation, where we have low level errors in certain