Type(pattern) annotations for Ruby

main.rb

require 'pattern-match'

class Module
  def check(pattern, mid)
    prepend Module.new {
      define_method(mid) do |*args|
        ret = super(*args)
        match(ret) do
          with(Kernel.eval(pattern, Kernel.binding)) { ret }
        end
      end
    }
  end
end

class C
  check '_[Integer]',
  def m
    [0]
  end
end

C.new.m