einblicker’s gists

einblicker / gist:1433783

Created December 5, 2011 14:38

sameLength

	trait Forall3[X[_, _, _]] {
	def apply[U, V, R]: X[U, V, R]
	}

	type ZipWith[A[_]] = {
	type Apply[U, V, R] = ((U, V) => R) => (A[U], A[V]) => A[R]
	}

	type Result[T] = (A[T], A[T], Forall3[ZipWith[A]#Apply]) forSome { type A[_] }

einblicker / gist:1485205

Created December 16, 2011 08:55

An observer pattern library by family polymorphism

	//library code
	//references: http://lamp.epfl.ch/~odersky/papers/ScalableComponent.pdf
	abstract class SubjectObserver {
	type S <: Subject
	type O <: Observer
	abstract class Subject { this: S =>
	private var observers: List[O] = List()
	def subscribe(obs: O) =
	observers = obs :: observers
	def publish =

einblicker / gist:1516748

Created December 24, 2011 07:57

sameLength(3)

	object Test extends App {
	sealed trait Nat
	case class Zero private (dummy: Zero) extends Nat
	case class Succ[T <: Nat] private (dummy: Succ[T]) extends Nat

	sealed abstract class Vec[L <: Nat, +T]
	case object VNil extends Vec[Zero, Nothing]
	case class VCons[L <: Nat, +T](head: T, tail: Vec[L, T]) extends Vec[Succ[L], T]

	def fromList[T, R](l: List[T])(k: (Vec[A, T] forSome {type A <: Nat}) => R): R = {

einblicker / gist:1516993

Created December 24, 2011 09:32

sameLength(4)

	object Test extends App {
	object Vec {
	def fromList[A](l: List[A]): Vec[_, A] = Vec(l)
	}

	case class Vec[Tag1, A] private (private val l: List[A]) {
	def toList = l

	def zipWith[Tag2, B, C](v: Vec[Tag2, B])(f: (A, B) => C)(implicit ev: Tag1 =:= Tag2) =
	Vec[Tag1, C](l.zip(v.l).map{case (a, b) => f(a, b)})

einblicker / gist:1520982

Created December 26, 2011 11:57

resumption monad

	object ResumptionMonad extends App {
	sealed abstract class Resumption[A] {
	def map[B](k: A => B) = flatMap(k andThen Val.apply)
	def flatMap[B](k: A => Resumption[B]): Resumption[B] = {
	def loop(x: Resumption[A]): Resumption[B] =
	x match {
	case Val(value) => k(value)
	case Wrap(value) => Wrap(loop(value))
	}
	loop(this)

einblicker / gist:1521202

Created December 26, 2011 13:51

operational monad

	object OperationalMonad extends App {
	class Operational {
	type instr[A] <: { def run: A }
	sealed abstract class Program[A] {
	def map[B](k: A => B) = flatMap(k andThen Lift.apply)
	def flatMap[B](k: A => Program[B]): Program[B] = {
	Bind(this, k)
	}
	def run: A
	}

einblicker / gist:1522196

Created December 26, 2011 22:13

free monad

	import scalaz._
	import Scalaz._

	object FreeMonad extends App {
	class FreeMonad[F[_]: Monad] {
	sealed abstract class Free[A]
	case class Val[A](value: A) extends Free[A]
	case class Wrap[A](value: F[Free[A]]) extends Free[A]
	implicit val freeMonad = new Monad[Free] {
	def pure[A](x: => A) = Val(x)

einblicker / PropAst.scala

Created January 8, 2012 06:23

Skolemization

	package logic

	object PropAst {
	type Id = String
	sealed abstract class Term
	case class Const(name: Id) extends Term {
	override def toString = name
	}
	case class Var(name: Id) extends Term {
	override def toString = name

einblicker / gist:1597306

Created January 11, 2012 22:58

sameLength(5)

	class Vec(list: List[Double]) {
	case class Value(list: List[Double])
	val value = Value(list)

	def sameLength(x: Vec#Value): Option[Value] = {
	if (x.list.length == list.length) Some(Value(x.list))
	else None
	}

	def innerProd(x: Value): Double = {

einblicker / gist:1632170

Created January 18, 2012 09:36

多相再帰の例