Fancy is a dynamic, object-oriented programming language heavily inspired by Smalltalk, Ruby and Erlang that runs on the Rubinius VM.
Fancy Ruby JavaScript C
Pull request Compare This branch is 686 commits behind bakkdoor:master.
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Failed to load latest commit information.

#The Fancy Programming Language

(C) 2010, 2011 Christopher Bertels

Fancy is a dynamic, object-oriented programming language heavily inspired by Smalltalk, Ruby, Io and Erlang. It supports dynamic code evaluation (as in Ruby & Smalltalk), class-based mixins, (simple) pattern matching, runtime introspection & reflection, "monkey patching" and much more. It runs on Rubinius, the Ruby VM, and thus has first-class integration with Ruby's core library and any additional Ruby libraries that run on Rubinius, including most C-extensions.

It supports concurrency via the actor-model, including first-class futures and async message send semantics built into the language, similar to Io.

For a quick feature overview, have a look at doc/ There's also a work-in-progress tutorial/book on Fancy here:

Fancy's standard library is all written in Fancy (with some minor exceptions written in Ruby - see boot/fancy_ext). Have a look at the lib/ directory.

Fancy is still in development, the implementation has evolved from an interpreter written in C++ to a fully bootstrapped bytecode compiler for the Rubinius VM ( You can see the self-hosted compiler implementation in lib/compiler/.

If you want to help out, feel free to contact us:

For some example code have a look at the examples/ directory.

There's also lots of test coverage code. Have a look at the tests/ directory for these. The tests are written in FancySpec, a simple testing library (somewhat similar to Ruby's RSpec). FancySpec's implementation can be viewed in lib/fancy_spec.fy.

##Compiling / Installing from source: ###Dependencies:

  • Rubinius. You'll need at least version 1.2.1 for Fancy to work as expected. See for more information. If you want to take advantage of the latest VM improvements, we suggest using rvm and installing rbx-head. See for more information.
  • Rake.
  • GNU Bison ( version 2.4 and higher otherwise you will get a Segmentation fault ).
  • GNU Flex.

Given the tools & libraries mentioned above, Fancy should build without problems on most *nix systems. We successfully have built Fancy on Debian & Ubuntu, OpenSuSE and Mac OS X 10.5 and 10.6.

###Standard building procedure: Building Fancy is just that easy:

$ cd <fancy_source_path>
$ rake

This should go pretty fast. It actually compiles Fancy's standard library and compiler several times. Once via the bootstrap compiler written in Ruby (see boot/rbx-compiler/), and then via the self-hosted compiler (see lib/compiler/) itself.

Once the bootstrapping process is done, you can run the hello world example:

$ ./bin/fancy examples/hello_world.fy

##Some technical information: As the language is running on the Rubinius VM, Fancy shares the same runtime with Ruby. All of Fancy is built upon Ruby objects, so for example when you open the String class in Fancy, it's just Ruby's String class.

Because of this, and because in Fancy's standard library (lib/*.fy) we can define methods with the same name as they're defined in Ruby (but taking no arguments), we have decided not to overwrite the Ruby methods. This ensures that all Ruby libraries for example can use Ruby's Kernel#print or any other method in Ruby's kernel and work seamlessly.

Here's an example:

    class Object {
      def print {
        "Print itself to the Console."
        Console print: self

To meet this goal, the Fancy compiler renames Fancy methods taking no arguments (like the previous "print" example) to a method named ":print". Using explicit parens syntax will allow you to invoke any Ruby method.

    someObject print    # Will actually invoke the Fancy ":print" method.
    someObject print()  # With explicit parens invokes the Ruby method.

Ruby method invocation supports passing a block variable to Ruby as a proc.

    class Something {
      def open: block {
        someRubyMethod(arg0, arg1, &block)
    Something new open: |s| { s work }

    # with this syntax, calling ruby's inject is just as easy.
    # This example will print the number 6
    [1, 2, 3] inject(0) |sum, num| { sum + num } println

##What's already working?

  • Class definitions (including nested classes that work like modules / namespaces)
  • Instance & class method definitions
  • Default arguments
  • Literal syntax for:
    • Strings, Symbols, Integers, Floats, Arrays, Hashes (HashMaps), Blocks (closures), Ranges, Tuples, Regular Expressions
  • Method & Operator calls
  • Instance & class variable access
  • Dynamically scoped variables (dynamic scoping)
  • Dynamic getter and setter method definitions (similar to Ruby's attr_acessor)
  • Loops (including next & break)
  • Support for closures via Blocks
  • Local & non-local returns from Blocks & Methods
  • File reading and writing
  • Class-Mixins (including methods of one class into another)
  • Exception handling (try, catch, finally & retry)
  • Simple pattern matching (work-in-progress)
  • Calling, using and extending arbitrary Ruby classes and methods (including C-extensions), as well as passing blocks and splat arguments to Ruby methods.
  • Futures (future = object @ message)
  • Async message sends (object @@ message)

##How is it implemented?

  • The lexer & parser are built with GNU Flex & GNU Bison. And used as a Ruby c-extension from Rubinius. The parser simply invokes methods on Fancy::Parser to build the AST. See: lib/parser/ext/parser.y & lib/parser/methods.fy

  • Once the AST is built, we use Rubinius' excellent compiler chain to compile it to bytecode.

  • The bin/fancy file is simply a Rubinius code loader for .fy files.

##Copyright: Fancy is licensed under the terms of the BSD license. For more information on licensing issues have a look at the LICENSE file.