Functional Programming With Ruby

I like Ruby, and I like functional programming, but if you try to shoehorn statelessness into your Ruby programs, you will be fighting the language, and you will feel a lot of pain. All of the data structures are ephermal, even strings. So, the language will not give thet persisitent, relatively perfomant strutuctes that Haskell or Clojure provides. If you want functional Ruby, just go use Clojure.

Other than recommending #map, #select, et al, the rest is poor advice. Consider the following recommendation

  input.inject({}) do |hash, item|
    hash.merge(item => process(item))
  end

Far, far slower, more memory intensive (big deal, given ruby's gc), and uglyer than the sane (and commonly accepted)

  Hash[input.map do |item|
    [item, process(item)]
  end]