ErlyJS - translating Javascript to Erlang

I have lately invested many hours of coding in ErlyJS, my open source attempt of writing a Javascript compiler for the Erlang virtual machine and crossed today the barrier of 100, for the number of commits and also for the number of test cases. There is still a long way to go, because nobody (including myself) will actually use the compiler in a real project, unless it is 100% Javascript compliant. But at least, most of the basic stuff is now halfway implemented:

• Literals
• Global / local variable handling
• Operators (except of dot operator, for objects)
  
• Functions
• Built-in global functions

The next big task will be object handling (and implementing the built-in objects and their functions)

I am not targeting the Erlang VM directly (beside of the Erlang compiler source code, there doesen't exist any formal specification or at least documentation about the Erlang VM internals in general and specifically the VM opcodes). What I do is transforming the Javascript source code AST to an Erlang AST. This involves a lot of trickery, because Erlang doesn't allow variable re-assignments (this is good and also necessary in the context of Erlang concurrency), but most Javascript code is just a bunch of variable re-assignments, so I have to model it somehow and I have choosen to model it differently for global Javascript variables (Erlang process dictionary) and local variables (normal Erlang variables). One interesting thing about having an Erlang AST of Javascript source code is the possibility of pretty-printing Erlang source code. Let's take a look at a Javascript example from the test cases:

function test() {
var a=0, b="Bananas";

switch (b) {
case "Oranges":
a = 1;
break;
case "Apples":
a = 2;
break;
case "Papayas":
case "Bananas":
a = 2.5;
a = 3;
break;
default:
a = 4;
}

return a;
}

If I pretty print the AST (just before compiling it, and this is even done automatically at verbose ErlyJS compiling settings) I get the following Erlang source code:

js_test() ->
V78 = 0,
V80 = "Bananas",
{V152} = case V80 of
         "Oranges" -> V170 = 1, {V170};
         "Apples" -> V88 = 2, {V88};
         X when X == "Papayas"; X == "Bananas" ->
             V270 = 2.5, V288 = 3, {V288};
         _ -> V32 = 4, {V32}
       end,
V152.

This kind of source code translation is extremely useful while developing and debugging the ErlyJS compiler and analyzing test cases.