* ClojureScript Day #1
* Important things to note
** This should be a dialog, not a lecture
*** stop me, ask questions, understand deeply
** There are still many things I don't know or haven't decided
*** some tasks will be research
*** some pushback welcome
**** I reserve BDFL rights :)
** This is an opportunity to get involved early
*** stay flexible to avoid pain
** Welcome Chouser!
*** One of my first and best users and contributors
*** Someone whose opinions I value, and a Clojure expert
*** Author of a Clojure book not (yet) working at Relevance!
*** The first to walk down the ClojureScript road
** This is a key Clojure/core (with help) deliverable
*** We do more than maintain, we lead
**** community should be stunned (shhh!)
*** I'm very excited about this aspect
**** let's knock this out of the park!
* Intro and rationale
** Problem statement
*** Javascript is the only programmable technology in key target environments
**** i.e. the browser
**** nothing will change that for years to come
*** Javascript has the greatest reach in other key environments
**** i.e. mobile
*** Javascript (the language) is not very robust
**** Fewer good parts than bad parts
**** Much convention and discipline required to avoid headaches
**** Conventions differ between shops, libs
*** Ever increasing pressure to create richer applications in these environments
**** requiring more and larger libraries
***** ordinary minification doesn't scale up
**** increasing requirements complexity
***** can't add language or environment complexity on top
** Rationale
*** solving this problem will give developers important leverage
*** empower them to tackle more difficult problems
**** with greater confidence in the robustness of their solutions
*** inspire next-generation approaches to web and mobile development
* Strategy
** Compile (a subset of) Clojure to Javascript
*** reach everywhere JS does
** Clojure is simpler, more robust, more concise, more powerful overall than JS
*** yet maps well to JS as implementation artifact
** Leverage best-of-breed JS appraoches
*** Currently, IMO that is Google's, with Closure compiler and libraries
**** called gclosure hereafter
*** Fortunately both open sourced
*** Gclosure's strategy is whole-program optimization
**** resulting application includes only code actually used
**** this is essential to writing large (and small) applications against large and manifold libraries
***** while allowing those libs to be written in a straightforward, non-clever manner
** This is not just about the browser
*** Node.js, plugins anywhere JS is accepted, any future JS-based environments
** Non-objectives
*** complete Closure
**** subset, but try to make identical features identical
**** document differences
*** porting large applications in their entirety
**** portability layers unifying JS and Java
**** cross platform reach is about moving core competencies and libraries, not everything
** Profit!
*** ClojureScript becomes the most powerful language for generating the smallest and fastest JS applications
**** ClojureScript runs everywhere JS runs
*** This is Clojure's client story
*** This is Clojure's mobile story
*** A powerful tool for anyone willing to learn Clojure
* Tactics
** Don't change Clojure itself
*** even though it might make things easier
**** track those things we'd like to be different, and work into Clojure dev schedule
** The ClojureScript compiler is written in Clojure
*** The reader is Clojure's
*** Macros are written in Clojure
*** therefor, no compiler at runtime, *no eval*
**** browser-hosted REPL a non-target!
*** also, some things that are runtime-reified in Clojure (namespaces, Vars) may not be in ClojureScript
** GClosure's strategy requires JS to be written in a particular idiom
*** especially for the most advanced optimization
*** ClojureScript will always generate code compliant with advanced optimizations
*** ClojureScript will use the same packaging and dependency strategy as gclosure
** The gclosure library is an accepted dependency
*** but *nothing else* (other than base JS)
**** ok, and maybe some stealing from GWT output, if we're desperate
***** but that's really it
*** in particular, use gclosure for all environmental conditionality
**** we make no per-browser decisions ourselves
** The gclosure compiler is optional, but recommended for final delivery
*** but don't be too stupid without it
** The compiler has an enriched primitive set (vs Clojure's)
*** deftype
*** defprotocol
*** extend-type
*** need no runtime lib
**** allows bootstrap abstraction and data structures to be written in terms of these
** The runtime library is completely written in ClojureScript
*** No Javascript!
*** js* primitive escape hatch to reach gnarly stuff that ClojureScript won't expose
** Presumptions
*** JS is single-threaded, forever
**** nevertheless, we will use Clojure reference primitives (at least atom)
* Roadmap
** Compiler
*** It's alive!
*** a few more primitives to go
*** output needs to be sussed out
**** esp tested with gclosure compiler
*** some niceties missing (load-file etc)
** Libraries
*** Many core macros imported and work
**** testing required
**** some missing, like binding, dotimes
*** This space intentionally left blank (core.cljs)
**** that's why you're here!
**** Much work, but following trodden ground
***** Move the core abstractions to protocols
***** Implement the core data structures with deftype
***** copy fn impls, tweaking as needed
** Tooling
*** ClojureScript written to the spec of gclosure
*** Actual integration with tool chain TODO
**** Deps builder
**** Compilation with gclosure compiler
***** drive through API for greatest control vs CLI
**** finding/loading gclosure lib
**** testing
**** delivery
*** REPL and other expected dev conveniences
**** load (file), load-js
* Inside the compiler 
** I will not be the only one who knows this!
*** only 500 lines
** [[http://en.wikipedia.org/wiki/Recursive_descent_parser][Recursive descent parser]]
** 2 phases
*** analyze
**** code data in -> AST data out
***** all ordinary Clojure data
**** each expr recursively analyzes nested exprs
**** checks for correct structure
*** emit
**** AST data in -> print JS (via side effect to *out*)
***** this allows with-out-str, or direct to file
***** alternative - thread output stream, meh
**** each expr recursively emits nested exprs
** Both analyze and emit are polymorphic
*** using multimethods
*** other than a little hand-routing at top of analyze, no global switch statement
**** extend the compiler by defining parse and emit methods
**** add special ops to specials set
** The threaded environment (env)
*** most important, :context and :locals
*** all name-introducing exprs (e.g. fn, let) augment the environment before passing to children
** Tricky bit - :context
*** In ClojureScript everything is an expression
**** but not in JS
**** optimal output requires knowledge of the context
***** :statement, :return, :expr
**** non-exprs in expr contexts require transformation (usually a function wrapper)
** Primitives walkthrough
*** if
*** def
*** fn*
*** do
*** let*
*** loop*
*** recur
*** new
*** set!
*** ns
*** deftype*
*** .
*** js*
** Macros walkthrough
*** macroexpansion
*** defprototype
*** extend-type
*** import-macros
*** the core/core trick
** Evaluation model
*** top down, form at a time
**** just like Clojure
**** just like JS
** What's missing?
*** validation that compilation ns resolved names exist in ns
*** more correctness checking
*** better error messages
**** ...
*** strategy for apply
* What's where
** src/main/clojure/cljs/compiler.clj
*** the compiler
** src/main/clojure/cljs/core.clj
*** core macros
** src/main/cljs/core.cljs
*** core library
* Todo
** separate org file
* Breakout and tackle tasks
** we'll substantially be in the same file
*** ideas for making that work?
* Regroup and feedback