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 the early development phase, 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 bolderplate code
• Support for keyword arguments and default values
• Simple system to prevent garbage collector conflicts

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:

require "anyolite"

MrbState.create do |mrb|
  test_module = MrbModule.new(mrb, "TestModule")

  MrbWrap.wrap_class(mrb, Entity, "Entity", under: test_module)

  MrbWrap.wrap_constructor_with_keywords(mrb, Entity, {:hp => {Int32, 0}})

  MrbWrap.wrap_property(mrb, Entity, "hp", hp, Int32)

  MrbWrap.wrap_instance_method_with_keywords(mrb, Entity, "damage", damage, {:diff => Int32})

  MrbWrap.wrap_instance_method_with_keywords(mrb, Entity, "yell", yell, {:sound => String, :loud => {Bool, false}})

  MrbWrap.wrap_instance_method_with_keywords(mrb, Entity, "absorb_hp_from", absorb_hp_from, {:other => Entity})

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

The last line in the block calls the following example script:

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

b = TestModule::Entity.new(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 syntax stays mostly the same as in Crystal, except for the keyword arguments. These might be added in the future, but technically you can always wrap the generated methods in pure Ruby methods with keywords.

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
• Returning objects of a wrapped class does only work if every constructor argument is optional
• Arrays, hashes and other complex mruby objects are not directly supported
• Configuration options for mruby are relatively limited (yet)
• Default values for unnamed function arguments are limited to integers and floats
• Optional keyword arguments need a default value (can be a different one than the Crystal value, though)
• Keywords will always be given to functions, even if optional (then with default values)
• Splat arguments and arbitrary keywords are not possible due to compiletime symbols in Crystal
• Only one type per argument is allowed

Why this name?

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

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

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

Roadmap

Releases

Version 0.2.0

Major features

• Keyword argument support
• Support for optional keywords

Minor features

• Casting from MrbValue objects to closest Crystal values
• Option to use a JSON config file

Breaking changes

• Optional arguments are passed using tuples instead of MrbWrap::Opt

Safety

• Class checks for arguments
• Checks for correct keyword classes
• Module cache analogous to the class cache

Usability

• Simplified some macro functions considerably
• Arguments can be specified consistently as arrays or standalone
• Documentation builds only for releases
• Uniform system for passing optional arguments
• Updated examples and documentation for keyword support

Bugfixes

• Fixed erros when naming MrbState instances anything other than 'mrb'

Version 0.1.1

Safety

• Added safeguards for reference table access

Bugfixes

• Fixed mruby function return values not being cached
• Fixed minor documentation errors

Version 0.1.0

Major features

• Basic structure
• Ubuntu support
• Wrappers for classes
• Wrappers for modules
• Support for classes in modules
• Wrappers for properties
• Wrappers for instance methods
• Wrappers for module and class methods
• Wrappers for constants
• Optional values for simple argument types
• Crystal GC respects the mruby GC
• Hooks for mruby object creation and deletion
• Simple examples
• Build tests
• Basic documentation

Upcoming releases

Currently none planned

Future updates

• [ ] Windows support (currently not supported due to problems with Crystal)
• [ ] Mac support (might be possible, not tested yet)
• [ ] Compiletime errors for macros
• [ ] Support for more flexible mruby configuration options
• [ ] Arrays as arguments and return values
• [ ] MrbClass/MrbModule and Class can be both used as arguments
• [ ] More stable type casting

Possible future updates

• [ ] Other types (Hashes, ...) as arguments and return values
• [ ] Option for passing mruby splat arguments as an array
• [ ] Support for arbitrary keyword arguments as hashes
• [ ] More variety for default parameters for unnamed options
• [ ] Method in mruby to determine owner of object (if possible)