Frank Thomas fthomas

As compiled by Kevin Wright a.k.a @thecoda

(executive producer of the movie, and I didn't even know it... clever huh?)

please, please, please - If you know of any slides/code/whatever not on here, then ping me on twitter or comment this Gist!

This gist will be updated as and when I find new information. So it's probably best not to fork it, or you'll miss the updates!

Monday June 16th

There is a great purely functional streaming/IO library in Scala called scalaz-stream. It is itself based upon a Haskell library called machines. They provide powerful abstractions to express compositional effectful computations. These libraries rely on certain type system features in both Scala and Haskell which are unavailable in F# - namely existential types and higher kinds. Higher kinds allow the monad representing the side-effects to be abstracted over. If however we specialize this to a specific monad, we can get around the lack of existentials as well.

Tomas Petricek created a type called asynchronous sequence which provides similar capabilities. The F# AsyncSeq type is declared as follows:

type AsyncSeq<'a> = Async<AsyncSeqInner<'a>>

and AsyncSeqInner<'a> = 
    | Nil
 | Cons of 'a * AsyncSeq&lt;'a&gt;

Rough Notes about CQRS and ES

Once upon a time…

I once took notes (almost sentence by sentence with not much editing) about the architectural design concepts - Command and Query Responsibility Segregation (CQRS) and Event Sourcing (ES) - from a presentation of Greg Young and published it as a gist (with the times when a given sentence was heard).

I then found other summaries of the talk and the gist has since been growing up. See the revisions to know the changes and where they came from (aka the sources).

It seems inevitable to throw Domain Driven Design (DDD) in to the mix.

Introduction to scalaz-stream

Every application ever written can be viewed as some sort of transformation on data. Data can come from different sources, such as a network or a file or user input or the Large Hadron Collider. It can come from many sources all at once to be merged and aggregated in interesting ways, and it can be produced into many different output sinks, such as a network or files or graphical user interfaces. You might produce your output all at once, as a big data dump at the end of the world (right before your program shuts down), or you might produce it more incrementally. Every application fits into this model.

The scalaz-stream project is an attempt to make it easy to construct, test and scale programs that fit within this model (which is to say, everything). It does this by providing an abstraction around a "stream" of data, which is really just this notion of some number of data being sequentially pulled out of some unspecified data source. On top of this abstraction, sca

require-from-twitter

Since Twitter doesn't have an edit button, it's a suitable host for JavaScript modules.

How to use

Source tweet: https://twitter.com/rauchg/status/712799807073419264

const leftPad = await requireFromTwitter('712799807073419264');

	object Demo {
	// A couple of type classes with type members ...
	trait Foo[T] {
	type A
	}

	object Foo {
	implicit val fooIS = new Foo[Int] { type A = String }
	}

	import cats.data.Xor
	import shapeless._
	import shapeless.ops.hlist.IsHCons
	import shapeless.tag.@@

	trait Predicate[P, T] extends Serializable { self =>

	type Out

	def apply(x: T) : Out

	miles@frege:~$ ./shapeless.sh
	Loading...
	Welcome to the Ammonite Repl 0.5.2
	(Scala 2.11.7 Java 1.8.0_51)
	@ val l = 23 :: "foo" :: true :: HNil
	l: Int :: String :: Boolean :: HNil = ::(23, ::("foo", ::(true, HNil)))
	@

	scala> import cats.implicits._
	import cats.implicits._

	scala> (1 -> 2) === (1 -> 3)
	res0: Boolean = true

	scala> import scala.reflect.runtime.universe._
	import scala.reflect.runtime.universe._

	scala> showCode(reify { (1 -> 2) === (1 -> 3) }.tree)

	// Initial idea courtesy of @dwijnand
	// Improved by @fthomas

	sealed trait List[+T] {
	def head: Option[T]
	}

	final case class Cons[T](h: T, t: List[T]) extends List[T] {
	val head: Some[T] = Some(h)
	}