danclien

:paste
import scalaz._, Scalaz._, scalaz.Free.{Suspend, Return}


// Console grammar
sealed trait ConsoleF[+A]
object Console {
  case class WriteLine[A](msg: String, o: A) extends ConsoleF[A]
  case class ReadLine[A](o: String => A) extends ConsoleF[A]
}

jboner

# How Akka maps to EAI Patterns

Might be up for debate or just plain wrong. Just some notes I scribbled down some time ago. 

-----------------------------------------------------------------------------------------------------------------
EAI PATTERN                     AKKA PATTERN                  REFERENCE
-----------------------------------------------------------------------------------------------------------------
Point to Point Channel          Regular Actor Communication   http://www.eaipatterns.com/PointToPointChannel.html
Event-Driven Consumer           Regular Actor Receive         http://www.eaipatterns.com/EventDrivenConsumer.html
Message Selector                Actor with Stash              http://www.eaipatterns.com/MessageSelector.html

avibryant

Recent versions of Cloudera's Impala added NDV, a "number of distinct values" aggregate function that uses the HyperLogLog algorithm to estimate this number, in parallel, in a fixed amount of space.

This can make a really, really big difference: in a large table I tested this on, which had roughly 100M unique values of mycolumn, using NDV(mycolumn) got me an approximate answer in 27 seconds, whereas the exact answer using count(distinct mycolumn) took ... well, I don't know how long, because I got tired of waiting for it after 45 minutes.

It's fun to note, though, that because of another recent addition to Impala's dialect of SQL, the fnv_hash function, you don't actually need to use NDV; instead, you can build HyperLogLog yourself from mathematical primitives.

HyperLogLog hashes each value it sees, and then assigns them to a bucket based on the low order bits of the hash. It's common to use 1024 buckets, so we can get the bucket by using a bitwise & with 1023:

select

tonymorris

// Questions about \/ and Validation
object scalaz {

/*
This explanation might help. This is a compilable source file with revisions 
available at https://gist.github.com/tonymorris/8263051

Fact: All monads are applicative functors. As has been seen we can witness the
`Applicative` that arises from the `Monad` primitives. Let's illustrate this:

arosien

import scalaz._
import Scalaz._
import Free._

/** "Pure" interactions with a console. */
sealed trait Console[+A]
case class GetLine[A](k: String => A) extends Console[A]
case class PutLine[A](s: String, a: A) extends Console[A]

object Console {

seanparsons

import scalaz._,Scalaz._,scalaz.effect._,OptionT._,Kleisli._

type OptionTIO[+X] = OptionT[IO, X]

val reader1: ReaderT[Option, Int, String] = kleisli[Option, Int, String](n => n.toString.some)
val reader2: ReaderT[IO, Int, String] = kleisli[IO, Int, String](n => IO((n * 2).toString))

val convertedReader1: ReaderT[OptionTIO, Int, String] = reader1.mapK[OptionTIO, String](opt => optionT(IO(opt)))
val convertedReader2: ReaderT[OptionTIO, Int, String] = reader2.mapK[OptionTIO, String](io => io.liftM[OptionT])

YoEight

package deiko

import scala.concurrent.Future
import scala.concurrent.duration.Duration
import scalaz.concurrent.Task
import scalaz.stream._
import play.api.libs.iteratee._
import Process._

object Conversion {

nkpart

object ArgonautPlay {
  implicit val writeableJson: Writeable[Json] = {
    // TODO this should explicitly be a UTF-8 encoder
    val stringWriter = implicitly[Writeable[String]].transform
    Writeable((a: Json) => stringWriter(a.spaces2), Some("application/json; charset=utf-8"))
  }
}

coreyhaines

Computing
Paul E. Ceruzzi
ISBN: 9780262517676
  
Modeling Business Processes
Wil van der Aalst and Christian Stahl
ISBN: 9780262015387
	
The Reasoned Schemer
Daniel P. Friedman, William E. Byrd, and Oleg Kiselyov

retronym

sudo gem install keydown # optional, only needed if you update the markdown.
git clone git@github.com:retronym/talks.git
git clone -b topic/play-keydown git@github.com:retronym/replhtml.git && cd replhtml
sbt -Dkeydown.root=$PWD/../talks/scala-2.10 run
open http://localhost:8080