channingwalton

object MonoidHomomorphism extends App {

  import scalaz._
  import Scalaz._

  /**
   * Turn any null into the Zero value for its type
   */
  def nullAsZero[T: Monoid : Equal](a: T) = if (a == null) implicitly[Monoid[T]].zero else a

channingwalton

case class Foo[T](x: T) {
  def map[B](f: T => B) = Foo(f(x))
}

object OldWay {

  def combineLatest[T1, T2](e1: Foo[T1], e2: Foo[T2]): Foo[(T1, T2)] = Foo((e1.x, e2.x))

  def combineLatest[T1, T2, T3](e1: Foo[T1], e2: Foo[T2], e3: Foo[T3]): Foo[(T1, T2, T3)] =
    combineLatest(combineLatest(e1, e2), e3) map {

channingwalton

import scalaz._

object LensFu extends App {

  case class FieldValue[T](name: String, v: T)

  case class Field[T, F](name: String, lens: Lens[T, F]) {
    def >=>[G](field: Field[F, G]): Field[T, G] = Field(name + "." + field.name, lens >=> field.lens)
    def get(v: T): FieldValue[F] = FieldValue(name, lens.get(v))
    def set(a: T, b: F): T = lens.set(a, b)

channingwalton

module Main 

rev : Vect n a -> Vect n a
rev Nil = Nil
rev (x :: xs) = (rev xs) ++ (x :: Nil)

main : IO ()
main = putStrLn $ show $ rev [1,2,3]

fails to compile with

channingwalton

21:15:22.745 ERROR akka://ENSIME/user/$b o.e.s.SocketHandler - Error in socket reader: 
java.lang.NumberFormatException: For input string: "new Wo"
	at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65) ~[na:1.8.0_31]
	at java.lang.Integer.parseInt(Integer.java:580) ~[na:1.8.0_31]
	at java.lang.Integer.valueOf(Integer.java:740) ~[na:1.8.0_31]
	at org.ensime.server.FramedStringProtocol$class.readString(FramedStringProtocol.scala:39) ~[server_2.11-0.9.10-SNAPSHOT.jar:0.9.10-SNAPSHOT]
	at org.ensime.server.SwankProtocol.readString(SwankProtocol.scala:10) ~[server_2.11-0.9.10-SNAPSHOT.jar:0.9.10-SNAPSHOT]
	at org.ensime.server.S≈wankProtocol.read(SwankProtocol.scala:15) ~[server_2.11-0.9.10-SNAPSHOT.jar:0.9.10-SNAPSHOT]
	at org.ensime.server.SocketHandler$$anon$1.run(SocketHandler.scala:43) ~[server_2.11-0.9.10-SNAPSHOT.jar:0.9.10-SNAPSHOT]

channingwalton

import scalaz._
import Scalaz._
import scalaz.effects._

import java.io._

/**
 * Background reading:
 * http://www.stackmob.com/2011/12/scalaz-post-part-2/
 * http://blog.sigfpe.com/2007/11/io-monad-for-people-who-simply-dont.html

channingwalton

object Generics {
  import shapeless.HList
  import shapeless.Nat
  import shapeless.Nat._
  import shapeless._

  trait <[A <: Nat, B <: Nat]
  implicit def lt1[B <: Nat] = new <[_0, Succ[B]] {}
  implicit def lt2[A <: Nat, B <: Nat](implicit lt: A < B) = new <[Succ[A], Succ[B]] {}

channingwalton

object KleisliValidation extends App {
  import scalaz._
  import Scalaz._
  import scala.util.control.Exception._

  type EValidation[+T] = Validation[String, T]
  implicit val binding = new Bind[EValidation] {
    def map[A, B](fa: EValidation[A])(f: A => B): EValidation[B] = fa.map(f)
    def bind[A, B](fa: EValidation[A])(f: A => EValidation[B]): EValidation[B] = fa.flatMap(f)
  }

channingwalton

object KleisliValidation extends App {
  import scalaz._
  import Scalaz._
  import scala.util.control.Exception._

   implicit def vm = Validation.validationMonad[String]

  type EValidation[+T] = Validation[String, T]
  
  def toDouble(s: String): EValidation[Double] = allCatch.either(s.toDouble).fold(_.toString.fail, _.success)

channingwalton

@channingwalton Recently read »I, Robot« from Asimov. The short stories are entertaining and very thoughtful.

@channingwalton I would like a wizard where I tell it I like Asimov (especially Daneel and Giskard) and Clarke, and it recommends others.

@channingwalton pretty much anything by Alastair Reynolds. House of Suns is particularly great.

@channingwalton I’ve enjoyed the Laundry novels by Charles Stross.

@channingwalton "Wool" series by Hugh Howey.