README.md

lua.cr

Crystal bindings to Lua. Supports Lua 5.4 and higher (including Lua 5.5).

Installation

Lua development libraries must be installed on your system:

# macOS
brew install lua

# Ubuntu/Debian
sudo apt install liblua5.4-dev

# Arch Linux
sudo pacman -S lua

# Fedora
sudo dnf install lua-devel

Then add this to your application's shard.yml:

dependencies:
  lua:
    github: veelenga/lua.cr

Usage

First you need to require Lua:

require "lua"

Then you can run a chunk of Lua code:

Lua.run %q{
  local hello_message = table.concat({ 'Hello', 'from', 'Lua!' }, ' ')
  print(hello_message)
} # => prints 'Hello from Lua!'

Or run a Lua file and obtain results:

p Lua.run File.new("./examples/sample.lua") # => 42.0

Or even evaluate a function and pass arguments in:

lua = Lua.load
sum = lua.run %q{
  function sum(x, y)
    return x + y
  end

  return sum
}
p sum.as(Lua::Function).call(3.2, 1) # => 4.2
lua.close

You can also expose Crystal procs to Lua as global functions. Argument and return types are taken from the proc's signature, so values flow naturally between the two languages:

lua = Lua.load

lua.function "add", ->(x : Float64, y : Float64) { x + y }
lua.run "return add(3, 4)" # => 7.0

# closures capture local Crystal state
counter = 0
lua.function "tick", -> { counter += 1; nil }
lua.run "tick(); tick()"
counter # => 2

# method pointers work too
def greet(name : String)
  "Hi, #{name}"
end

lua.function "greet", ->greet(String)
lua.run "return greet('Lua')" # => "Hi, Lua"

lua.close

More features coming soon. Try it, that's fun :)

Contributing

1. Fork it https://github.com/veelenga/lua.cr/fork
2. Create a feature branch git checkout -b my-new-feature and implement your feature
3. Run tests crystal spec and format code crystal tool format
4. Commit your changes git commit -am 'Add some feature'
5. Push to the branch git push origin my-new-feature
6. Create a new Pull Request