v8ruby

A Ruby implementation that compiles Ruby to JavaScript and runs it on the V8 engine (via Node.js). Your Ruby program becomes JavaScript and is JIT-compiled and executed by V8 — so V8 really is the engine running Ruby.

$ v8ruby -e 'puts "Hello from V8 Ruby!"'
Hello from V8 Ruby!

How it works

Ruby source
   │  src/lexer.js      tokenize (handles interpolation, heredocs, %w[], symbols…)
   ▼
 Tokens
   │  src/parser.js     recursive-descent + Pratt precedence → AST
   ▼
  AST
   │  src/compiler.js   two-pass: (1) scope analysis for Ruby local-variable
   │                    semantics, (2) emit JavaScript
   ▼
JavaScript ──► new Function('R', js)(R) ──► executed on V8
                         │
                   src/runtime.js   the Ruby object model + core classes
                                     (Integer, Float, String, Symbol, Array,
                                      Hash, Range, Proc, Struct, Enumerator,
                                      Comparable, Enumerable, exceptions, …)

Every method call and operator is compiled to a single dynamic-dispatch entry point, R.send(recv, name, args, block), so Ruby semantics are preserved:

• Truthiness — only nil and false are falsy (0 and "" are truthy).
• Integer vs Float — 1 / 2 == 0 but 1.0 / 2 == 0.5.
• Everything is an object — 3.times, "x".upcase, nil.to_a.
• Open classes, method_missing, respond_to?, operator overloading.
• Blocks, procs, lambdas, yield, non-local return/break/next.
• super, modules/mixins (include), Comparable, Enumerable.
• Exceptions — begin/rescue/ensure/retry, custom exception classes.

Usage

./v8ruby program.rb        # run a file
./v8ruby -e 'puts 1 + 1'   # run a one-liner
./v8ruby --dump program.rb # print the generated JavaScript
./v8ruby -v                # version (shows the underlying V8 version)

Installed from npm (npm install -g v8ruby), the same command is available as v8ruby.

(No build step and no dependencies — just Node.js.)

Supported language features

Literals (int, float, string with #{} interpolation, symbols, arrays, hashes, ranges, %w[]/%i[], heredocs <<~), all operators, multiple assignment and destructuring, splat/keyword/block/default parameters, if/unless/case/ while/until/for, ternary, &&/||/and/or/not, method calls with and without parentheses, safe navigation &., blocks ({} and do…end), procs and stabby lambdas (->(){}), endless methods (def f = …), classes with inheritance and super, singleton/class methods (def self.x), modules, attr_accessor, Struct, class_eval/define_method, and a large slice of the core library.

See examples/ for sample programs and test/cases/ for feature tests.

Tests

test/run.js is a differential test runner: it runs each test/cases/*.rb through both v8ruby and the real ruby interpreter (if installed) and diffs the output.

node test/run.js

Limitations

This is a from-scratch implementation of a large language; it targets the common core, not 100% of MRI. Notable gaps: no real threads/fibers, no full Regexp (simple String#match/gsub only), Rational/Complex are approximate, mutation of frozen objects isn't enforced, and only a subset of the enormous standard library is present.

License

MIT