Anyolite

Anyolite is a Crystal shard which adds a fully functional mruby interpreter to Crystal.

Description

Anyolite allows for wrapping Crystal classes and functions into mruby with little effort. This way, mruby can be used as a scripting language to Crystal projects, with the major advantage of a similar syntax.

This project is currently in active development, so please report any bugs or missing relevant features.

Features

• Bindings to an mruby interpreter
• Wrapping of nearly arbitrary Crystal classes and methods to mruby
• Easy syntax without unnecessary boilerplate code
• Simple system to prevent garbage collector conflicts
• Support for keyword arguments and default values
• Objects, structs, enums and unions as function arguments and return values are completely valid
• Methods and constants can be excluded, modified or renamed with annotations

Prerequisites

You need to have the following programs installed (and in your PATH variable, if you are on Windows):

• Ruby (for building mruby)
• Rake (for building the whole project)
• Bison (for building mruby)
• Git (for downloading mruby)
• GCC or Microsoft Visual Studio 19 (for building the object files required for Anyolite, depending on your OS)

Installing

Put this shard as a requirement into your shard.yml project file and then call

shards install

from a terminal or the MSVC Developer Console (on Windows).

Alternatively, you can clone this repository into the lib folder of your project and run

rake build_shard

manually to install the shard without using the crystal shards program.

If you want to use other options for Anyolite, you can set ANYOLITE_CONFIG_PATH to the filename of a JSON config file, which allows for changing multiple options when installing the shard. Possible options are:

• ANYOLITE_BUILDPATH - The relative directory in which Anyolite will be built
• ANYOLITE_MRUBY_FORK - The web address of the mruby repository
• ANYOLITE_MRUBY_DIR - The relative directory mruby will be installed in
• ANYOLITE_MRUBY_CONFIG_PATH - The config file which is used for building mruby
• ANYOLITE_COMPILER - The C compiler used for building Anyolite

How to use

Imagine a Crystal class for a really bad RPG:

module TestModule
  class Entity
    property hp : Int32 = 0

    def initialize(@hp)
    end

    def damage(diff : Int32)
      @hp -= diff
    end

    def yell(sound : String, loud : Bool = false)
      if loud
        puts "Entity yelled: #{sound.upcase}"
      else
        puts "Entity yelled: #{sound}"
      end
    end

    def absorb_hp_from(other : Entity)
      @hp += other.hp
      other.hp = 0
    end
  end
end

Now, you want to wrap this class in Ruby. All you need to do is to execute the following code in Crystal (current commit; see documentation page for the version of the latest release):

require "anyolite"

MrbState.create do |mrb|
  MrbWrap.wrap(mrb, TestModule)

  mrb.load_script_from_file("examples/hp_example.rb")
end

Well, that's it already. The last line in the block calls the following example script:

a = TestModule::Entity.new(hp: 20)
a.damage(diff: 13)
puts a.hp

b = TestModule::Entity.new(hp: 10)
a.absorb_hp_from(other: b)
puts a.hp
puts b.hp
b.yell(sound: 'Ouch, you stole my HP!', loud: true)
a.yell(sound: 'Well, take better care of your public attributes!')

The example above gives a good overview over the things you can already do with Anyolite. More features will be added in the future.

Limitations

• Currently, Anyolite does not work on Windows due to Crystal compiler bugs
• Arrays and hashes are not directly supported
• Symbols do not work due to their compiletime nature in Crystal
• Splat arguments and arbitrary keywords are not possible due to their reliance on symbols
• Regular function arguments are not very flexible (keyword arguments however are!)
• Keywords will always be given to functions, even if optional (then with default values)

Why this name?

https://en.wikipedia.org/wiki/Anyolite

In short, it is a rare variant of the crystalline mineral called zoisite, with ruby and other crystal shards (of pargasite) embedded.

The term 'anyoli' means 'green' in the Maasai language, thus naming 'anyolite'.

Roadmap

Upcoming releases

Version 0.7.0

Features

• [ ] Support for wrapping generics (unless impossible)

Breaking changes

• [ ] Find consistent solution for non-keyword arguments

Usability

• [ ] More helpful error messages when path resolution fails

Version 1.0.0

• [ ] Windows support (currently not supported due to problems with Crystal)
• [ ] Crystal specs for testing
• [ ] Mac support (might be possible, not tested yet)
• [ ] More configuration options for the Rakefile
• [ ] Documentation of all relevant features and wrappers

Future ideas (might not actually be possible to implement)

• [ ] Options for inherited and/or inheriting classes
• [ ] Arrays and/or hashes as argument and return values
• [ ] Splat argument and/or arbitrary keyword passing
• [ ] Method in mruby to determine owner of object