Fun with Recursive Anonymous Functions

Did you know that an anonymous function can call itself?

All you need is something like this:

factorial_of = -> (n) { n <= 1 ? 1 : n * factorial_of.call(n - 1) }
factorial_of.call(5)
# => 120

This came in handy when I had a recursive method which needed to be wrapped inside an enumerator to navigate a very complex hierarchy of objects.

Instead of something as complex as that, let’s wrap our anonymous factorial function around an enumerator:

factorial_of = -> (n) { n <= 1 ? 1 : n * factorial_of.call(n - 1) }

f = Enumerator.new do |y|
  num = 0
  loop do
    y << factorial_of.call(num)
    num += 1
  end
end

f.next
=> 1
f.next
=> 1
f.next
=> 2
f.next
=> 6

Now we can fetch the next number whenever we want, or enumerate over the numbers until we don’t have any left (which is infinite in this case)