Difference between revisions of "The JavaScript Problem"

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(Roy: add PureScript)
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* Support for various forms of code-generation
* Support for various forms of code-generation
=== Roy ===
=== Roy, PureScript ===
[http://roy.brianmckenna.org/ Roy]: meld JavaScript semantics with functional languages. Experimental, but has many bread-and-butter Haskell features. Probably does not generate efficient code.
[http://roy.brianmckenna.org/ Roy]: meld JavaScript semantics with functional languages. Experimental, but has many bread-and-butter Haskell features.
Roy is written in JS. PureScript is written in Haskell.
=== Idris ===
=== Idris ===

Revision as of 18:47, 3 November 2013

The problem

The JavaScript problem is two-fold and can be described thus:

  1. JavaScript sucks. The depths to which JavaScript sucks is well-documented and well-understood. Its main faults are: its lack of module system, weak-typing, verbose function syntax¹, late binding², which has led to the creation of various static analysis tools to alleviate this language flaw³, but with limited success⁴ (there is even a static type checker⁵), finicky equality/automatic conversion, this behaviour, and lack of static types. Coffeescript is the most mainstream javascript alternative. Although it makes many aspects of Javascript sane and convenient, it still suffers from weak-typing.
  2. We need JavaScript. Using it for what it is good for, i.e. providing a platform for browser development, but not using the language per se, is therefore desirable, and many are working to achieve this, in varying forms. There are various ways to do it, but we ought to opt for compiling an existing language, Haskell, to JavaScript, because we do not have time to learn or teach other people a new language, garner a new library set and a new type checker and all that Haskell implementations provide.

Updating this page

Please update and expand this page with the various attacks on this problem and their progress. The question of The JavaScript Problem comes up every so often and this should be the page to link people to.



Original blog post here. Quickstart guide here. A more in-depth discussion about the current capabilities of the backend here. For an example of using the JavaScript compilation for a real app see this blog post, there is also a port of wxAsteroids to the browser (see github or a blog post).

  • Beta.
  • Only works for UHC, but promising.
  • UHC compiles enough of Hackage to be very useful.
  • Doesn't produce an explosion of code, seemingly.
  • Fairly substantial JS/DOM/W3C/HTML5 API.
  • Currently works.


Website: http://fay-lang.org/ Discussion on Reddit: Fay slides. The package is on Hackage. Fetch with Git:

 git clone git://github.com/faylang/fay.git
  • Compiles a subset of Haskell, needs more
  • Currently works.


The Github page is here.

  • Alpha.
  • Works.
  • Incomplete.
  • Nicely designed.
  • Compiles most pure Haskell libraries no problem.
  • FFI to JS works, and the author, sviperll is a helpful guy.


Haste on GitHub, on Hackage, thesis.

  • Work in progress.
  • Generates relatively small and fast code.
  • Lightweight concurrency, Cabal integration, FFI and GHC extensions supported.
  • Cross platform.
  • Works.


On the Haskell wiki (see above) and on hackage

  • Mature
  • Works
  • Complete
  • Maintained
  • Not Haskell
  • Syntax is a fusion of Haskell and JavaScript
  • Untyped, but with syntactic correctness (at least) enforced at compile-time.
  • Embeddable through quasi-quoting
  • Support for various forms of code-generation

Roy, PureScript

Roy: meld JavaScript semantics with functional languages. Experimental, but has many bread-and-butter Haskell features. Roy is written in JS. PureScript is written in Haskell.


Idris is a compiled language with dependent types, implemented in Haskell, with backends for both LLVM and JavaScript. Experimental.

  • Full dependent types with dependent pattern matching where clauses, with rule, simple case expressions, pattern matching let and lambda bindings
  • Dependent records with projection and update
  • Type classes
  • Monad comprehensions
  • Syntactic conveniences for lists, tuples, dependent pairs do notation and idiom brackets
  • Indentation significant syntax
  • Extensible syntax
  • Tactic based theorem proving (influenced by Coq)
  • Cumulative universes
  • Totality checking
  • Simple foreign function interface (to C)
  • Hugs style interactive environment



  • Haskell interpreter in JS — An interpreter. Haven't tried but is apparently dead.
  • YHC JS backend — Beta-ish. Apparently works, but I was unable to compile YHC, so haven't tried yet. I would be interested in anyone's experience using it. There's an old wiki page about Yhc's JavaScript support, but Yhc itself is a dead project.
  • Emscripten — not Haskell→JS, but compiles LLVM/Clang output to JavaScript. Could possibly be used for GHC→LLVM→JS compiling, which I tried, and works, but would have to also compile the GHC runtime which is not straight-forward (to me) for it to actually run.
  • hjscript — Beta. EDSL, not Haskell→JS. Works. Not very annoying to program in, but is JS semantics, not Haskell. Hackage package here.
  • Some have also tried writing a Haskell→JS compiler to make a more direct JS-aware translation of code (to not have huge code output a la GHCJS, YHC, Emscripten).



  1. Its support for closures is commonly noted as being one of JavaScript’s redeeming features.
  2. Early binding allows for static verification of the existence of method-signature pairs (e.g. v-tables). Late binding does not give the compiler (or an IDE) enough information for existence verification, it has to be looked up at run-time.
  3. There are several hinting libraries, which developers insist are indispensable tools when developing JavaScript seriously, such as JavaScript lint, JSLint, and JSure.
  4. “Any non-trivial analysis is very difficult due to Javascript’s dynamic nature.” — Berke Durak, Ph.D., author of jsure.
  5. Google Inc. thought it necessary to develop a compiler, Google Closure, which does type-checking and limited inference.