Calling a Ruby method recursively from within its associated block. Any other way?

Question

I've come up with this:

def f x, &b
  yield x, b
end
f 4 do |i, b|
  p i
  f i - 1, &b if i > 0
end

Result:

4
3
2
1
0

Is there another way?

Answer 1

It depends upon the particulars of your actual code, but given your example, if you name the block beforehand, you can avoid yielding the value and the block in your function. Eg:

def f(x, &b)
  yield x
end

foo = lambda do |i|
  p i
  f(i-1,&foo) if i > 0
end
f(4,&foo)

However, I'd like to find a more elegant solution to this problem. I suspect this is would be a good application of the Y combinator. As soon as I have something better for you, I'll update this message.

Answer 2

def f(x, &b)
  b.call x
  f(x-1,&b) if x>0
end

f(4) do |x|
 p x
end