retronym

object test {

  case class L[A, B]() {
    def ToLub[AA >: A <: L, BB >: B <: L, L] = new { type LUB = L }
  }

  val intBoolLub = L[Int, Boolean].ToLub
                             
  (1: AnyVal) : intBoolLub.LUB
  1: intBoolLub.LUB

travisbrown

import shapeless._, Nat._

trait FizzBuzz[N <: Nat] {
  type R3 <: Nat
  type R5 <: Nat
 
  def ti: ToInt[N]
  def prev: List[String]
  def d3: R3 =:= _0
  def d5: R5 =:= _0

kmizu

trait TF {
  type Apply[A]
}
type Curry2[F[_, _]] = TF { type Apply[X] = TF { type Apply[Y] = F[X, Y] } }
type Curry3[F[_, _, _]] = TF { type Apply[X] = Curry2[(TF { type Apply[Y, Z] = F[X, Y, Z] })#Apply] }
// ...

type CurriedMap = Curry2[Map]

val x: CMap#Apply[String]#Apply[Int] = Map("x" -> 1, "y" -> 1) //It is valid code.

travisbrown

/**
* Type-level Tower of Hanoi
* by Travis Brown
*
* Note: not optimal, and probably won't work for some valid inputs.
* Tested with Scala 2.9.2 and Shapeless 1.2.3.
*/

import shapeless._, Nat._

puffnfresh

# Get yourself sbt-extras
# Or: brew install sbt
alias scalaz="sbt -sbt-create 'set libraryDependencies += \"org.scalaz\" %% \"scalaz-core\" % \"7.1.0-M4\"' 'set initialCommands := \"import scalaz._; import Scalaz._\"' 'console'"

johnynek

package mapreduce

/**
 * This is an attempt to find a minimal set of type classes that describe the map-reduce programming model
 * (the underlying model of Google map/reduce, Hadoop, Spark and others)
 * The idea is to have:
 * 1) lawful types that fully constrain correctness
 * 2) a minimal set of laws (i.e. we can't remove any laws,
 * 3) able to fully express existing map/reduce in terms of these types
 * 

travisbrown

import scala.language.experimental.macros
import scala.reflect.macros.Context
import shapeless._

object NatExample {
  def toNat(n: Int): Any = macro toNat_impl

  def toNat_impl(c: Context)(n: c.Expr[Int]) = {
    import c.universe._

YoEight

object Alacarte {
  trait Functor[F[_]]{
    def map[A, B](fa: F[A])(f: A => B): F[B]
  }
  
  trait Eval[F[_]] {
    def F: Functor[F]
	
    def evalAlgebra(fa: F[Int]): Int 
  }

travisbrown

/**
 * We can use the Scala type system (with help from Miles Sabin's Shapeless
 * library) to solve the bank account number validation problem in the second
 * user story of the KataBankOCR kata on Coding Dojo:
 * 
 * http://codingdojo.org/cgi-bin/wiki.pl?KataBankOCR
 * 
 * By Travis Brown in response to a question by Paul Snively on the Shapeless
 * Dev mailing list:
 *

raichoo

import scala.language.higherKinds

/*
 * The usual peano numbers with addtion and multiplication  
 */
sealed trait Nat {
  type Plus[N <: Nat] <: Nat
  type Mult[N <: Nat] <: Nat
}