Thanks! Agreed it feels like a good fit for Ruby as well!

RE the pattern matching stuff I think the destructuring concept could be applied to look something like:

    def div(*args)
      case args
      when Pattern{[a, 0]} then [:error, "can't divide by 0"]
      when Pattern{[a, 1]} then [:ok, Pattern.last.a]
      when Pattern{[0, b]} then [:ok, 0]
      when Pattern{[a, b]} then [:ok, Pattern.last.a / Pattern.last.b]
      end
    end

    def something(object)
      case object
      when Pattern{a[b, c]} then [:ok, Pattern.last.b + Pattern.last.c]
      else [:error, "a didn't contain b and c"]
      end
    end

Some shorthand to access `Pattern.last` e.g. "$~" for regex would make things even nicer!