Do something infinitely many times with an index

There’s a predefined (in 1.9.2) constant Float::INFINITY, so you could write

1.upto(Float::INFINITY) do |i|
  ...
end

(You could also use Enumerator and take_while, turning the problem inside out to make it look more like Haskell or Python, but take_while is greedy and builds an array.)

Ruby 2.5 introduced the open-ended Range:

(1..).each do |i|
  #...
end

Numeric.step has default parameters of infinity (the limit) and 1 (the step size).

1.step do |i|
  #...
end

For fun, you might even want to try

1.step.size