erikrozendaal’s gists

erikrozendaal / NewType.swift

Last active January 21, 2016 08:55

Swift helpers voor minimal boilerplace "new type" support

	//
	// Packages a value into a new, type-safe wrapper. The value can always be safely unwrapped.
	//
	public protocol NewType: CustomStringConvertible {
	// The type of the wrapped value
	typealias Unwrapped

	// Accessor for the underlying value
	var unwrapped: Unwrapped { get }

erikrozendaal / rle.idr

Created December 9, 2013 18:12

Run-length encoding in Idris

	rep : (n : Nat) -> a -> List a
	rep Z x = []
	rep (S k) x = x :: rep k x

	data RLE : List Char -> Type where
	REnd : RLE []
	RChar : (n : Nat) -> (c : Char) -> (rs : RLE xs) -> RLE (rep n c ++ xs)

	rle : (xs : List Char) -> RLE xs
	rle [] = REnd

erikrozendaal / gist:7354327

Last active December 27, 2015 16:19

Creating exceptions with and without stacktrace. Measured on a early 2013 MacBook Pro 13" retina.

	$ scala -cp Thyme.jar
	Welcome to Scala version 2.10.3 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_45).
	Type in expressions to have them evaluated.
	Type :help for more information.

	scala> val th = new ichi.bench.Thyme
	th: ichi.bench.Thyme = ichi.bench.Thyme@7464fb1c

	scala> th.pbenchOff[Exception]("stacktraces")(new Exception("foo") with scala.util.control.NoStackTrace, ftitle = "without")(new Exception("foo"), htitle = "with")
	Benchmark comparison (in 20.94 s): stacktraces

erikrozendaal / gist:6294954

Last active December 21, 2015 10:49

Scalaz equivalent to Hibernate's JSR-303 based @notempty annotation

	def notNull[A](a: A): Validation[String, A] =
	if (a != null) a.success else "may not be null".failure

	def size[A <% Traversable[_]](min: Int = 0, max: Int = Int.MaxValue)(a: A): Validation[String, A] =
	if (min to max contains a.size) a.success else s"size must be between $min and $max".failure

	// Composing notNull and size, like https://github.com/hibernate/hibernate-validator/blob/master/engine/src/main/java/org/hibernate/validator/constraints/NotEmpty.java#L48
	def notEmpty[A <% Traversable[_]](a: A): Validation[String, A] =
	notNull(a) flatMap size(min = 1)

erikrozendaal / delete

Last active December 18, 2015 06:59

Performance of initial implementation in-memory B-Tree vs the standard Scala Red-Black Tree implementation used by TreeSet. The B-Tree is about 5 times more memory efficient, so it works better for large sets due to memory locality effects. Update: initial delete implementation + benchmark numbers added.

-Benchmark comparison (in 9.612 s): delete 1 shuffled values
-    btree vs treeset
-Significantly different (p ~= 0)
-  Time ratio:    0.76712   95% CI 0.73631 - 0.79793   (n=20)
-    btree      78.60 ns   95% CI 75.96 ns - 81.25 ns
-    treeset    60.30 ns   95% CI 58.98 ns - 61.62 ns
-Benchmark comparison (in 13.16 s): delete 10 shuffled values
-    btree vs treeset
-Significantly different (p ~= 7.567e-11)
-  Time ratio:    1.06081   95% CI 1.04667 - 1.07495   (n=20)

erikrozendaal / build.sbt

Last active December 13, 2015 23:19

Type driven development - an example Use a recent version of `sbt` to load the example into the scala console: $ sbt console scala> import timeseries._ scala> println(accountTotals)

	name := "timeseries"

	scalaVersion := "2.10.0"

	libraryDependencies ++= Seq(
	"joda-time" % "joda-time" % "2.1",
	"org.joda" % "joda-convert" % "1.3")

erikrozendaal / CommitPublisher.scala

Created July 22, 2012 12:32

Event sourcing example - part 2

	/**
	* Publishes successful commits to subscribers.
	*/
	trait CommitPublisher[Event] {
	/**
	* Notifies `listener` of all commits that happened `since`. Notification happens asynchronously.
	*/
	def subscribe(since: StoreRevision)(listener: Commit[Event] => Unit): Subscription
	}

erikrozendaal / Post.scala

Created July 1, 2012 18:55

Event sourcing example - part 1

	/**
	* A specific blog post with its current content.
	*/
	case class Post(id: PostId, content: PostContent)

	/**
	* The current state of blog posts, derived from all committed PostEvents.
	*/
	case class Posts(byId: Map[PostId, Post] = Map.empty, orderedByTimeAdded: Seq[PostId] = Vector.empty) {
	def get(id: PostId): Option[Post] = byId.get(id)

erikrozendaal / lenses.scala

Created June 17, 2012 12:03

Lenses in Scala with support for Maps, Seqs, and JSON (using the Jerkson library)

	package lenses

	import com.codahale.jerkson._, AST._

	/**
	* Lenses allow retrieving and updating values of type `B` inside some enclosing value of type `A`.
	*
	* Since lenses can be composed together, arbitrary nesting is automatically taken care of.
	*/
	case class Lens[A, B](get: A => B, set: (A, B) => A) {

erikrozendaal / 1.sql

Created February 18, 2012 14:21

Play! 2.0

	# --- !Ups

	create table users (
	name text primary key,
	age int not null);

	# --- !Downs

	drop table users;

Erik Rozendaal erikrozendaal