ceedubs

working with the fork and pull-request model on GitHub

The common model for contributing to an open-source project is the fork/pull request model. In this model, if you want to contribute to a project, you don't need commit rights to the projects GitHub repository. Instead, you "fork" the repository to create your own copy. You make your changes in your own fork and then submit a "pull request" (PR) which is a request that your changes get merged into the main repository. The fork/PR model is beneficial even in a work environment, as it allows fine-grained control over repository permissions while still allowing non-owners to contribute. See GitHub's About collaborative development models and its "Further reading" section for more information.

This document gives some tips for:

• cloning (making a local copy of) a repository
• forking (making a remote copy of) a repository
• [fetching pull request code](#f

ceedubs

import HList._

sealed abstract class HList
case object HNil extends HList
final case class HCons[H, T <: HList](head: H, tail: T) extends HList

object HList {
  type HNil = HNil.type
  type ::[H, T <: HList] = HCons[H, T]

ceedubs

import cats.free.Trampoline, Trampoline._
import cats.implicits._

def isEven(xs: List[Int]): Trampoline[Boolean] =
  if (xs.isEmpty) done(true) else suspend(isOdd(xs.tail))

def isOdd(xs: List[Int]): Trampoline[Boolean] =
 if (xs.isEmpty) done(false) else suspend(isEven(xs.tail))

// returns true (doesn't overflow the stack)

ceedubs

object CurryInference {
  implicit final class OptionOps[A](val oa: Option[A]) {

    /** curried fold */
    def curriedFold[B](z: => B)(f: A => B): B = oa.fold(z)(f)

    /** uncurried fold */
    def uncurriedFold[B](z: => B, f: A => B): B = oa.fold(z)(f)
  }

ceedubs

trait Show[A] {
  def show(a: A): String
}

object Show {
  implicit val stringShow: Show[String] = new Show[String] {
    def show(a: String) = a
  }
}

ceedubs

trait Show[A] {
  def show(a: A): String
}

object Show {
  implicit val stringShow: Show[String] = new Show[String] {
    def show(a: String) = a
  }
}

ceedubs

package shapeless.examples

import shapeless._
import nat._
import ops.hlist._

object TableExample {

  final case class Row[L <: HList](cells: L)

ceedubs

import scalaz._
import shapeless._
import shapeless.ops.hlist._

/** contrived IndexedState example */
object HStack extends App {
  def push[H, T <: HList](h: H): IndexedState[T, H :: T, H] =
    IndexedState(t => (h :: t, h))

  def pop[H, T <: HList]: IndexedState[H :: T, T, H] =

ceedubs

object FreeCTwoRandomIntExample extends App {
 
  import scalaz._
  import scalaz.effect.IO
  import scala.util.Random

  sealed trait Action[A]
  final case class Log(msg: String) extends Action[Unit]
  final case class RandomInt(below: Int) extends Action[Int]

ceedubs

object WriterTExample extends App {

  import scalaz._
  import scalaz.effect.IO
  import scala.util.Random
  import scalaz.syntax.monad._

  type Logged[F[_], A] = WriterT[F, DList[String], A]

  def log[F[_]](msg: => String)(implicit F: Applicative[F]): Logged[F, Unit] =