cr-wren

This is a binding to embed the Wren language into Crystal and call Wren code from Crystal and viceversa.

Why Wren

Wren is a small, fast, class-based, concurrent scripting language.

I like the syntax much better than Lua's or Javascript's and it's a fairly powerful language with decent performance.

Installation

This is a WIP, I may end up vendoring wren inside this project.

Install wren as a library in your system.
- In Arch: yay install wren
- In other systems: Embedding instructionshtml#embed-the-vm

Add the dependency to your shard.yml:

dependencies:
  cr-wren:
    github: ralsina/cr-wren

Run shards install

Usage

This is a fully commented example:

require "../src/wren.cr"  # Adjust as needed

vm = Wren::VM.new "myvm"

# We can just tell the VM to interpret (run) code
vm.interpret "main", "System.print(\"Hello World!\")"

# This defines a function in Wren
vm.interpret "main", %(
  var add = Fn.new { |a,b|
    return a+b
  }
)

# And we can call it from Crystal
puts vm.call("main", "add", "call", [1, 2])     # => 3.0
puts vm.call("main", "add", "call", ["1", "2"]) # => "12"

# This fails with a runtime error even when the equivalent Wren code works
# probably a bug somewhere
# puts vm.call("main", "add", "call", [[1, 2], [3, 4]]) # => [1,2,3,4]


# Register a Crystal proc to add floats into the Wren VM
vm.register_function(
  "main", "Math", "add",
  Wren::VM.wrap("myvm", ->(a : Float64, b : Float64) : Float64 {
    a + b
  })
)

# Register a proc to add 3 floats. We can register the same proc more than
# once with the same name and different arity
vm.register_function(
  "main", "Math", "add",
  Wren::VM.wrap("myvm", ->(a : Float64, b : Float64, c : Float64) : Float64 {
    a + b + c
  })
)

# We also need to declare it as "foreign" in Wren.
vm.interpret "main", %(
  class Math {
    foreign static add(a,b)
    foreign static add(a,b,c)
  }
)

# And we can call it on Wren, which will use the Crystal code
vm.interpret "main", %(
  System.print("2+3.5=")
  System.print(Math.add(2,3.5))
  System.print("1+2+3=")
  // We can pass a string as argument here because cr-wren will cast it to Float64
  System.print(Math.add("1",2,3))
) # 2+3.5=5.5  ¨1"+2+3=6