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// Passing an extra argument into a polymorphic function?
// http://stackoverflow.com/questions/39628068/passing-an-extra-argument-into-a-polymorphic-function/39637253#39637253

object Main extends App {
  import shapeless._, shapeless.poly.~>

  val lists = List(1,2) :: List("A", "B") :: List(1.1, 2.2) :: HNil

  {
    class sss(i: Int) extends (List ~> Set) {

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// Pick out the Nth element of a HList of Lists and return that value as a HList of values
// http://stackoverflow.com/questions/39584034/pick-out-the-nth-element-of-a-hlist-of-lists-and-return-that-value-as-a-hlist-of/39594978#39594978

object Main extends App {
  import shapeless._

  val a = List(1,2,3) :: List("a", "b", "c") :: List(true, false, true) :: HNil

  trait RowSelect[L <: HList] extends DepFn2[L, Int] {
    type Row <: HList

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object Main extends App {
  val f = (_: Int) * 2
  val g = (_: Int) + 2
  val h = (_: Int) * 3

  {
    import scalaz.{IList, Endo}
    import scalaz.syntax.foldable._

    val hh = IList(

n4to4

// https://www.scala-exercises.org/doobie

import doobie.imports._
import scalaz._, Scalaz._
import scalaz.concurrent.Task
import shapeless._

object Main extends App {
  val program = 42.point[ConnectionIO]
  val xa = DriverManagerTransactor[Task](

n4to4

// https://github.com/adelbertc/faq/blob/master/src/main/tut/typeclasses.compiled.md

object Main extends App {
  def sumInts(list: List[Int]): Int = list.foldRight(0)(_ + _)

  def concatStrings(list: List[String]): String = list.foldRight("")(_ ++ _)

  def unionSets[A](list: List[Set[A]]): Set[A] = list.foldRight(Set.empty[A])(_ union _)

  trait Monoid[A] {

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object Main extends App {
  type II = Int \/ Int

  def l(idx: Int): II = { println(s"l($idx)"); 0.left }
  def r(idx: Int): II = { println(s"r($idx)"); 1.right }

  var idx = -1
  val xs: Stream[II] = Stream(0, 0, 1, 0, 1) map { x => idx += 1; if (x == 0) l(idx) else r(idx) }

  def leftIsLeft()

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import scalaz._, Scalaz._

object Main extends App {
  implicit class verbose[A] (a: A) {
    def v[B](log: B): A = {
      println(log)
      a
    }
  }

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// http://stackoverflow.com/questions/39794943/map-hlist-with-default/39795173#39795173

import shapeless._

case class Foo()

trait Wrapper

case class S(s: String) extends Wrapper
case class I(i: Int) extends Wrapper

n4to4

import shapeless._
import scalaz._, Scalaz._

object Main extends App {
  case class Foo(x: String, y: Int, z: Boolean)
  case class Bar(x: String, y: Int, z: Boolean)

  val fooGen = Generic[Foo]
  val barGen = Generic[Bar]

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import scalaz._, scalaz.syntax.show._
import atto._, Atto._

object Main extends App {
  case class Prof[A](
    name: String,
    age: Int,
    students: List[A]
  )