Clojure/West 2013

About me

1. Patch.com
2. Scala all day
3. MFA in Writing
   • From an art school

About Clojure/West

• March 18-20
• Portand, OR
• Alex Miller
• One-night miniKanren Confo
• Talks will be released on InfoQ

Links

• This slide: bit.ly/clojure-west-links
• GitHub repo of Clojure/West slides
• Stuart Sierra's "Perils of Dynamic Scope" as a blog post
• Mindbat's notes: day 1, 2, 3
• Clojure Gazette's notes
• Pedestal: repo, slides (some pictures taken from here)
• ClojureScript-in-ClojureScript: repo, slides
• SynThread: repo, slides

Trending topics

• Logic (constraint? declarative?) programming
• FRP
• ClojureScript
• Monads
• How to build good things well

Pedestal

Yes, it's a web application framework.

Pedestal provides a better, cohesive way to build rich client web applications in Clojure.

Three cool things about Pedestal.

1. Event rewind and replay in the browser
2. Interceptors: better ring handlers
3. App Model

Events

Chat sample app.

Open this link twice (once in an incognito window).

Remember the JS console!

Interceptors

A different take on Ring middleware.

Ring

• Ring is a library for abstracting the details of HTTP. Like Python's WSGI or Ruby's Rack.
• Handler: A function that takes a request (a map) and returns a response (also a map).
• Middleware: A function that takes a handler and returns a handler.

Middleware example

Problems with middleware

• Middleware calls other middleware directly. It has that knowledge and responsibility.
• Inside a middleware, you don't know anything about the chain of middleware it's in.
• Middleware chains are bound to the thread they start on.

Interceptors

      (defrecord Interceptor
        [name enter leave error pause resume])
    

• Interceptor fns operate on contexts which contain all data associated with the processing of the request, including the Ring request and response
• Since the context describes processing, it can be paused on one thread and resumed in another.

What about ring?

• Many popular middlewares ported to use enter/leave.
• Convenience methods for porting exiting middleware.
• Trying to get Ring to move to this model.

App Model

• App state is modeled as a tree.
• Event messages are translated into tree deltas.
• UI code uses those deltas.
• Everything else is pure functions.

ClojureScript

ClojureScript is a compiler for Clojure that targets JavaScript.

CLJS compilation as a service

(defmacro unless [expr & body] `(if ~expr nil (do ~@body)))

ClojureScript-in-ClojureScript

ClojureScript-in-ClojureScript is a port of the Clojure parts of the ClojureScript compiler to ClojureScript. Led by Joel Martin.

CLJS in the browser

(defmacro unless [expr & body] `(if ~expr nil (do ~@body)))

What's done (some highlights)

• The Reader
• defmacro
• ns support
• File I/O support
• so, a lot

The path to self-hosting

Most things compile except for some tricky macro/var/namespace interactions in core.clj/core.cljs

After self-hosting

• Merge back into clojure/clojurescript
• Keep moving towards Clojure-in-Clojure
  • ClojureScript moved some from Java to Clojure
  • ClojureScript-in-ClojureScript is moving even more

But...

• What's a CLASSPATH to JavaScript?
• Replace Google Closure Compiler?
• ClojureScript will forever be a subset of Clojure