folone

Scalaz
Symbol	Code	Ascii	Example
η	951	pure	1.η[List]
μ	03BC	join	List(List(1,2,3), nil, List(5,6,7)) μ
∅	2205	zero	∅[Int]
<∅>		empty	<∅>[Option, Int]
∙	2219	contramap	((_:String).length ∙ (_:Int).toString ∙ ((_:Int) + 6))(5)
∘	2218	map	(((_:Int) + 6) ∘ (_:Int).toString ∘ (_:String).length)(5)
∘∘

"map2":https://github.com/scalaz/scalaz/blob/master/core/src/main/scala/scalaz/MA.scala#L326

folone

/**
 * <b>Fixed Point Combinator is:</b>
 * Y = λf.(λx.f (x x)) (λx.f (x x))
 * 
 * <b>Proof of correctness:</b>
 * Y g  = (λf . (λx . f (x x)) (λx . f (x x))) g    (by definition of Y)
 * = (λx . g (x x)) (λx . g (x x))                  (β-reduction of λf: applied main function to g)
 * = (λy . g (y y)) (λx . g (x x))                  (α-conversion: renamed bound variable)
 * = g ((λx . g (x x)) (λx . g (x x)))              (β-reduction of λy: applied left function to right function)
 * = g (Y g)                                        (by second equality) [1]

folone

$ ghci
GHCi, version 7.4.2: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Prelude> :l hello-ski.hs 
[1 of 1] Compiling Main             ( hello-ski.hs, interpreted )
Ok, modules loaded: Main.
*Main> main
Hello world!

folone

def ackermann(m: Int, n: Int): Int = {
   (m, n) match {
     case (0, _)                   ⇒ n + 1
     case (m, 0) if m > 0          ⇒ ackermann(m - 1, 1)
     case (m, n) if m > 0 && n > 0 ⇒ ackermann(m - 1, ackermann(m, n - 1))
   }
 }
 
import scalaz._, Scalaz._, Free.{suspend ⇒ _, _}, Trampoline._
def ackermannTramp(m: Int, n: Int): Trampoline[Int] = {

folone

// Updated for Scala 2.10.0.
def kind[A: scala.reflect.runtime.universe.TypeTag](a: A): String = {
  import scala.reflect.runtime.universe._
  def typeKind(sig: Type): String = sig match {
    case PolyType(params, resultType) =>
      (params map { p =>
        typeKind(p.typeSignature) match {
          case "*" => "*"
          case s   => "(" + s + ")"
        }

folone

### Keybase proof

I hereby claim:

  * I am folone on github.
  * I am folone (https://keybase.io/folone) on keybase.
  * I have a public key whose fingerprint is 3A57 D1D4 67F6 0189 3CB7  03D8 FA5C 9955 37B3 71EF

To claim this, I am signing this object:

folone

import scalaz._, Scalaz._

case class Happy[A](a: A)
case class NewYear(year: Int)

implicit val happyInstance = new Applicative[Happy] {
  def point[A](a: ⇒ A) = Happy(a)
  def ap[A, B](fa: ⇒ Happy[A])(f: ⇒ Happy[A => B]) =
    f match {
      case Happy(f) ⇒ fa match {

folone

> shapeless-core/console
[warn] Credentials file /home/folone/.ivy2/.credentials does not exist
[info] Compiling 24 Scala sources to /home/folone/workspace/shapeless/core/target/scala-2.11/classes...
[info] Starting scala interpreter...
[info] 
Welcome to Scala version 2.11.0-20130205-141957-132e09fc2e (OpenJDK 64-Bit Server VM, Java 1.7.0_09).
Type in expressions to have them evaluated.
Type :help for more information.

scala> import shapeless._

folone

> shapeless-examples/console
[warn] Credentials file /home/folone/.ivy2/.credentials does not exist
[warn] Binary version (2.10) for dependency org.scala-lang#scala-library;2.10.2
[warn] 	in com.chuusai#shapeless_2.10.2;2.0.0-SNAPSHOT differs from Scala binary version in project (2.10.2).
[warn] Binary version (2.10) for dependency org.scala-lang#scala-compiler;2.10.2
[warn] 	in com.chuusai#shapeless_2.10.2;2.0.0-SNAPSHOT differs from Scala binary version in project (2.10.2).
[info] Starting scala interpreter...
[info] 
Welcome to Scala version 2.10.2 (OpenJDK 64-Bit Server VM, Java 1.7.0_40).
Type in expressions to have them evaluated.

folone

final val BATCH_SIZE = (Runtime.getRuntime.freeMemory / 1024).toInt // kb per object should be enough, right?

def doStuff(m: MyType): Stream[MyType] = ??? // Costly operation
val s: Stream[MyType] = ???
s.grouped(BATCH_SIZE).toStream.flatMap(_.par flatMap doStuff)