Awesome

toy

This is a tiny interpreter (with a bytecode compiler and a stack-based virtual machine) for a lilliputian subset of JavaScript, written in C and... JavaScript itself. It fits in less than 2500 lines of code.

The parser and the bytecode generator (in compile.js) are written in Toy-compatible JavaScript. It was just too painful to write those in C. Since you can run them with Node.js or Toy itself, they self-compile (into compiler_code.c) and are magically bundled inside the toy executable.

Interesting features

• Closures
• Compiles itself (see above)
• Little mark-and-sweep garbage collector

Unsupported JavaScript features

• ES201{5,6,7}
• Functions with many arguments (use lists, dictionnaries or curryfication instead)
• Prototypes
• Exceptions
• undefined (seriously, who needs undefined? null is sufficient)
• Optional semicolons
• Booleans (use 0 and 1, or anything else truthy or falsy)
• for, switch, do
• else (just write if statements. Thousands of if statements.)
• Regexps

Compile and run

You need Node.js, a C compiler and GNU make. Just run make and try the examples.

Various observations

First of all, because I hate naming things à la JavaScript:

• an object, a hash map or a hash table is dictionnary
• an array is a list

For the sake of simplicity, the whole thing is really slow.

The dictionnary implementation is a shame.

Lists are implemented with those dictionnaries. This is really straightforward since we need dictionnaries and JavaScript lists behaves mostly the same. It’s obviously slow.

Since the garbage collector does not visit the stack, each object has a reference counter which prevents it from being collected if that counter is nonzero. Moreover, the GC must not run at any time, but only between two instructions (see the call to request_garbage_collection(); in vm.c).

Variables are compiled as-is. The VM interprets scoping rules and catches variable definition errors at run-time. The compiler is really straightforward.

I just hope you are not crazy enough to use this hack in production.

Why?

It was fun. Enjoy :wink: