bwmcadams

import com.mongodb.casbah.Imports._

val conn = MongoConnection()

val db = conn("test")

val coll = db("foo")

for (x <- coll.find(MongoDBObject("_id" -> new ObjectId("4cd2d357c575954934c5a975")), 
          MongoDBObject("x" -> 1))) println(x)

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]

viktorklang

trait Enum { //DIY enum type
  import java.util.concurrent.atomic.AtomicReference //Concurrency paranoia

  type EnumVal <: Value //This is a type that needs to be found in the implementing class

  private val _values = new AtomicReference(Vector[EnumVal]()) //Stores our enum values

  //Adds an EnumVal to our storage, uses CCAS to make sure it's thread safe, returns the ordinal
  private final def addEnumVal(newVal: EnumVal): Int = { import _values.{get, compareAndSet => CAS}
    val oldVec = get

raichoo

class MMethod[M, A1, A2, R](f: (A1, A2) => R) {                                                                      
  def apply(a1: A1, a2: A2): R = f(a1, a2)
}

class MultiMethod {
  def apply[A1, A2, R](a1: A1, a2: A2)
                      (implicit mm: MMethod[this.type, A1, A2, R]): R =
    mm(a1, a2)

  // use a singleton type to attach the resulting implicit to our multimethod

debasishg

/**
 * |@| is a helper function that helps you accumulate applicative functors. It gives you an ApplicativeBuilder (it's part of
 * the implementation though) through which you accumulate your applicatives just as you would using the Builder pattern of
 * the GoF in the OO world. Once you have all the applicatives you can pass it a function that will be applied to all the 
 * values that you have accumulated so far. e.g.
 */

scala> (1.some |@| 2.some) apply {_ + _}
res1: Option[Int] = Some(3)

corruptmemory

/**
 * A silly example using Kleisli composition of DB operations
 * Based on an idea from Runar Bjarnason found here:
 *   https://groups.google.com/d/msg/scala-debate/xYlUlQAnkmE/FteqYKgo2zUJ
 *
 * Uses Scalaz7
 *
 * @author <a href="mailto:jim@corruptmemory.com">Jim Powers</a>
 */
object Monadic {

jboner

Latency Comparison Numbers (~2012)
----------------------------------
L1 cache reference                           0.5 ns
Branch mispredict                            5   ns
L2 cache reference                           7   ns                      14x L1 cache
Mutex lock/unlock                           25   ns
Main memory reference                      100   ns                      20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy             3,000   ns        3 us
Send 1K bytes over 1 Gbps network       10,000   ns       10 us
Read 4K randomly from SSD*             150,000   ns      150 us          ~1GB/sec SSD

viktorklang

import scala.concurrent._
import scala.collection.mutable.Builder
import scala.collection.generic.CanBuildFrom
import language.higherKinds

/**
 * Linearize asynchrnously applies a given function in-order to a sequence of values, producing a Future with the result of the function applications.
 * Execution of subsequent entries will be aborted if an exception is thrown in the application of the function.
 */
def linearize[T, U, C[T] <: Traversable[T]](s: C[T])(f: T => U)(implicit cbf: CanBuildFrom[C[T], U, C[U]], e: ExecutionContext): Future[C[U]] = {

mpilquist

import scalaz._
import Scalaz._
import scalaz.iteratee._
import EnumeratorT._

def counter[A, F[+_]: Pointed] =
  IterateeT.fold[A, F, Int](0) { (acc: Int, a: A) => acc + 1 }

def count[A, F[+_]: Monad](e: EnumeratorT[A, F]) =
  (counter[A, F] &= e).run

robinsloan

require "rubygems"
require "twitter"
require "json"

# things you must configure
TWITTER_USER = "your_username"
MAX_AGE_IN_DAYS = 1 # anything older than this is deleted

# get these from dev.twitter.com
CONSUMER_KEY = "your_consumer_key"