sshark’s gists

sshark / bintree.hs

Last active June 26, 2016 15:45

Simple binary tree implementations. Using ideas from http://learnyouahaskell.com/making-our-own-types-and-typeclasses#recursive-data-structures

	data Tree a = Empty \| Node a (Tree a) (Tree a) deriving Show

	append :: Ord a => a -> Tree a -> Tree a
	append a Empty = (Node a Empty Empty)
	append a (Node v left right)
	\| a > v = Node v left (append a right)
	\| a < v = Node v (append a left) right
	\| a == v = Node v left right

	nodes = foldr append Empty [8,6,4,1,7,3,1,5]

sshark / numbers.scala

Last active January 23, 2016 16:07

Demonstrate how typeclasses are used to manage existing types and implement new unforeseen types

	trait Num[A] extends Ordering[A] {
	def plus(a:A,b:A):A
	}

	def plus[T: Num](a: T, b: T):T = implicitly[Num[T]].plus(a,b)
	def cmp[T:Ordering](a: T,b: T):Int = implicitly[Ordering[T]].compare(a,b)

	implicit object DoublePlus extends Num[Double] {
	override def plus(a:Double, b:Double) = a + b
	override def compare(a:Double, b:Double) = a.compare(b)

sshark / TypeLambda.scala

Created May 7, 2016 18:46

Type lambda example. Further explanation found in http://like-a-boss.net/2014/09/27/type-lambda-in-scala.html

	trait Functor[F[_]] {
	def map[A, B](x: F[A])(f: A => B): F[B]
	}

	implicit def optionFunctor: Functor[Option] = new Functor[Option] {
	override def map [A, B](x: Option[A])(f: A => B): Option[B] = x map f
	}

	implicit def tuple2Functor[X] = new Functor[({type Alias[A] = Tuple2[X, A]})#Alias] {
	override def map[A, B](t: Tuple2[X, A])(f: A => B): Tuple2[X, B] = (t._1, f(t._2))

sshark / mt-example.scala

Last active May 15, 2016 11:18

Scalaz Monad Transformer Example from https://softwarecorner.wordpress.com/2013/12/06/scalaz-optiont-monad-transformer/



	import play.api.libs.concurrent.Execution.Implicits.defaultContext
	import scala.concurrent.Future
	import scalaz._
	import Scalaz._

	type IntState[A] = State[Int, A]

	case class Song(name: String, durationInSeconds: Int)

sshark / MonadicAndApplicationValidation.scala

Last active May 18, 2016 11:38

How to use Scalaz EitherT and \/ both monadically and applicatively to validate inputs

	import scalaz._
	import Scalaz._
	import scala.concurrent.Future
	import scala.concurrent.ExecutionContext.Implicits.global

	case class Order(id: Long, desc: String)
	case class Vendor(id: Long, name: String)

	def delay[A](f: => Future[A], duration: Long, message: String) = {
	println(message)

sshark / ReaderWithFutureOption.scala

Last active June 7, 2016 12:45

Uses of Reader Monad in combination with other monads

	import scalaz._
	import Scalaz._
	import scala.language.higherKinds
	import scala.concurrent.Future
	import scala.concurrent.ExecutionContext.Implicits.global

	trait Session {
	def doSomething(): Unit
	}

sshark / kleisli.scala

Last active June 5, 2016 14:58 — forked from jto/kleisli.scala

For future reference on Kleisli

	import scalaz._
	import Scalaz._
	import scala.concurrent.Future
	import scalaz.std.scalaFuture._
	import play.api.libs.concurrent.Execution.Implicits._

	val f1 = (s: String) => Option("foo").point[Future]
	def f2 = (s: String) => Option(1).point[Future]

	type OptionTFuture[T] = OptionT[Future, T]

sshark / IOExample.scala

Last active June 15, 2016 07:42

Simple IOMonad hack adopted from http://underscore.io/blog/posts/2015/04/28/monadic-io-laziness-makes-you-free.html

	import iomonad.Pure
	import iomonad.Pure.IO

	val io =
	for {
	_ <- Pure.println("Starting work now.")
	// Do some pure work
	x = 1 + 2 + 3
	_ <- Pure.println("All done. Home time.")
	} yield x

sshark / trampoline.scala

Last active June 23, 2016 11:59

Trampoline for Recursion between 2 Functions (Bouncing)

	import scala.annotation.tailrec
	import scala.math.Numeric.Implicits._

	sealed trait Thunk[A]
	case class Done[A](x: A) extends Thunk[A]
	case class Cont[A](f: () => Thunk[A]) extends Thunk[A]

	def evenT[A: Numeric](i: A)(implicit f: Int => A): Thunk[Boolean] = if (i == 0) Done(true) else Cont(() => oddT(i - 1))
	def oddT[A: Numeric](i: A)(implicit f: Int => A): Thunk[Boolean] = if (i == 0) Done(false) else Cont(() => evenT(i - 1))

sshark / Employee.java

Last active October 23, 2017 07:24

How <T extends Comparable<T>> or similar declaration is used

	package acme;

	public class Employee implements Comparable<Employee> {
	@Override
	public int compareTo(Employee o) {
	return 0;
	}
	}

TH Lim sshark