Haskell-like list comprehensions in Ruby

raskell.rb

$stack, $draws = [], {}

def method_missing *args
  return if args[0][/^to_/]
  $stack << args.map { |a| a or $stack.pop }
  $draws[$stack.pop(2)[0][0]] = args[1] if args[0] == :<
end

class Array
  def +@
    $stack.flatten!
    keys = $draws.keys & $stack
    draws = $draws.values_at *keys

    comp = draws.shift.product(*draws).map do |draw|
      $stack.map { |s| draw[keys.index s] rescue s }.reduce do |val, cur|
        op = Symbol === cur ? [:send, :method][val.method(cur).arity] : :call
        val.send op, cur
      end
    end

    $stack, $draws = [], {}
    Symbol === last ? comp.select(&pop) : comp
  end

  def -@
    case map(&:class).index Range
    when 0 then first.to_a
    when 1 then [first] + last.step(last.min.ord - first.ord).to_a
    else self
    end
  end
end

foo  =+ [x * y | x <- [1..3], y <- [4..6]]
# [4, 5, 6, 8, 10, 12, 12, 15, 18]

bar  =+ [a + b | a <- ['n','p'..'t'], b <- %w[a i u e o]]
# ["na", "ni", "nu", "ne", "no", "pa", "pi", "pu", "pe", "po", "ra", "ri", "ru", "re", "ro", "ta", "ti", "tu", "te", "to"]

baz  =+ [i ** 2 / 3 | i <- [3,6..100], :even?]
# [12, 48, 108, 192, 300, 432, 588, 768, 972, 1200, 1452, 1728, 2028, 2352, 2700, 3072]

quux =+ [s.size.divmod(2) | s <- %w[Please do not actually use this.]]
# [[3, 0], [1, 0], [1, 1], [4, 0], [1, 1], [2, 1]]

Wow, I'm amazed. I really wish Ruby supported this style.

Nice work. Let's see if this can be made fly with 2.0...

Really cool!

Yuck

Bonus points for the name!

Amazing! Some comments would be useful, though.

so cool!

So, what about using it in place of function argument?

Like:
[x * y | x <- [1..3], y <- [4..6]].each { |a| print a }

Ruby 2.1!

Looks really nice!

I played a bit with the idea to get that. Trying out ruby2 refinements. Too lazy for the "|" support but can do conditions.
https://gist.github.com/freakhill/5564328

+1 for "Raskell". Pun in "Rascal"?

Awesome job! ❤️ Gem it please?

"Haskell-like" without lambdas?
Even if it doesn't look as much like Haskell, this snippet is much closer to the Haskell principles, without abusing Ruby.

foo = ->(x=(1..3), y=(4..6)){x.flat_map{|a| y.map{|b| a*b}}}.call

(Of course you usually wouldn't need to call any lambdas before actually executing the application)

Nice but for Ruby I prefer using Ruby syntax:

(1..3).zip(4..6).map { |a, b| a * b }

I'd humbly like to up-vote the previous comment.

Thats quite brilliant, the author does say "Please do not actually use this."
@hauleth zip is a bit different, list comprehensions are more like cross products:

(1..3).to_a.product((4..6).to_a).map{|a,b| a*b}

or you could do a double map_flat like @wteuber.

Impressive.