...

• Target the Google Closure AST
  • Advantages
    • Keeps us out of the JS AST design business
    • Existing code printer
    • Includes facilities for Closure Compiler type system
    • Perf? Can skip roundtrip to JS source and to disk
  • Disadvantages
    • Closure AST nodes are stateful
      • Each Node has an explicit parent reference
      • Cloning policy is necessary to reuse subtrees (wasn't an issue in my port so far, see below)
    • Increases our dependence on Closure
      • Closure AST evolves more quickly than the JS spec
      • Recent changes: http://code.google.com/p/closure-compiler/source/list?path=/trunk/src/com/google/javascript/jscomp/parsing/IRFactory.java&start=2295
  • Alternative: Intermediate JavaScript AST as Clojure data-structures
    • Requires an additional translation step
    • GWT and Dart use a different AST that they translate; See: http://code.google.com/p/google-web-toolkit/source/browse/trunk/dev/core/src/com/google/gwt/dev/js/ClosureJsAstTranslator.java?r=10778
  • Closure Compiler Discussion: https://groups.google.com/forum/?fromgroups=#!topic/closure-compiler-discuss/OEwLWkw4Kug
• Thin JS-AST DSL
  • Recursively transpiles arguments
  • Can be extended to automatically attach source mappings from dynamic bindings
  • Does a Hiccup like seq expansion
  • Eliminate js* form, replaces it with DSL invokes: (js* "foo({0})" x) becomes (js*/call 'foo x)

Preliminary Progress

• Fork: https://github.com/brandonbloom/clojurescript/tree/js-ast
  • Interesting files: compiler.clj and js.clj
• As of Nov 9
  • Compiles all the CLJS in the ClojureScript tree
  • Bugged in advanced compilation mode
  • Does not generate source mappings
  • Does not bypass the extra round-trip to JS source and to disk
  • Takes 3X as long as naive string printing; 10 vs 30 seconds for (compile-root "src/cljs/cljs") on my machine
  • core.clj and core.cljs are fully ported from (js* "..." ...) to (js*/... ...)