Steven Shaw steshaw

Difference Lists

Proposed BFPG lightning talk. 25 slides, 5 minutes, 12 seconds per slide. No problem!

September 2014

1

Motivation: we want to write something as clear as this, but this is O(n^2).

Running a Craft site on Fastly

Fastly is essentially Varnish as a service. Similarly to how Heroku drastically simplifies the running of a web server, Fastly simplifies full-page caching of websites with running with dynamic content.

How Fastly Works

In a nutshell:

Every time there is a request for your website, it is routed through Fastly instead of directly to your backend.
If Fastly has an existing cache for the requested URL, it serves the cached page and your backend isn't touched at all.

From section 9 of John Backus's 1977 Turing Award lecture Can Programming Be Liberated from the von Neumann Style? A Functional Style and Its Algebra of Programs:

Denotational semantics and its foundations provide an extremely helpful mathematical understanding of the domain and function spaces implicit in programs. When applied to an applicative language (...), its foundations provide powerful tools for describing the language and for proving properties of programs. When applied to a von Neumann language, on the other hand, it provides a precise semantic description and is helpful in identifying trouble spots in the language. But the complexity of the language is mirrored in the complexity of the description, which is a bewildering collection of productions, domains, functions, and equations that is only slightly more helpful in proving facts about programs than the reference manual of the language, since it is less ambiguous.

...

Thus

The introduction to Reactive Programming you've been missing

(by @andrestaltz)

This tutorial as a series of videos

If you prefer to watch video tutorials with live-coding, then check out this series I recorded with the same contents as in this article: Egghead.io - Introduction to Reactive Programming.

	DR650	DR-Z400	XR650	KTM690	WR450	TE510
Highway handling	9	5	7	9	3	1
Highway engine	9	6	6	7	4	2
Carrying	9	5	5	6	3	2
Off-road handling	2	6	4	7	8	9
Off-road engine	5	7	6	7	8	9
Up-front cost	9	9	8	2	5	2
Ongoing cost	9	8	8	2	4	2

	module FizzBuzzC

	%default total

	-- Dependently typed FizzBuzz, constructively

	-- A number is fizzy if it is evenly divisible by 3
	data Fizzy : Nat -> Type where
	ZeroFizzy : Fizzy 0
	Fizz : Fizzy n -> Fizzy (3 + n)

	-- Code taken from http://stackoverflow.com/questions/12735274/breaking-data-set-integrity-without-generalizednewtypederiving/12744568#12744568
	-- Discussion on haskell-cafe: http://thread.gmane.org/gmane.comp.lang.haskell.cafe/100870
	-- http://www.haskell.org/pipermail/haskell-cafe/2012-October/103984.html
	-- Modified to remove orphan instances by rwbarton

	module A where
	data U = X \| Y deriving (Eq, Ord, Show)
	data T u b c = T u b c deriving (Eq, Show)

	-- Demonstrates how to ensure coherence when representing typeclasses with first-class dictionaries

	newtype Tag t a = Tag { untag :: a } -- constructor kept private
	use :: a -> (forall t . Tag t a -> b) -> b -- tagged values introduced in a stack discipline

	-- Example, a 'first-class' Ord

	newtype Ord a = Ord { ordering :: a -> a -> Ordering }

	-- Ensure coherence when using this with Set

	object ScalaJSExample extends js.JSApp{
	def main() = {
	val xs = Seq(1, 2, 3)
	println(xs.toString)
	val ys = Seq(4, 5, 6)
	println(ys.toString)
	val zs = for{
	x <- xs
	y <- ys
	} yield x * y

	%default total

	class Semigroupy a where
	op: a -> a -> a
	semigroupOpIsAssociative : (x, y, z : a) -> op x (op y z) = op (op x y) z

	instance Semigroupy Int where
	op = (+)
	semigroupOpIsAssociative x y z = believe_me "sure, yeah, whatever"