Clojure's -> in Ruby (not that you'd ever really do it :P)

thread_first.rb

#!/usr/bin/ruby

# http://clojuredocs.org/clojure_core/clojure.core/-%3E
# http://clojuredocs.org/clojure_core/clojure.core/-%3E%3E

def thread_first(val, *args)
    args.inject(val) { |acc, arg|
        if val.is_a? Hash
            acc = acc[arg]
        else
            if arg.is_a? Array
                if arg.last.is_a? Proc
                    acc = acc.send(arg[0], *arg[1...-1], &arg[-1])
                else
                    acc = acc.send(arg[0], *arg[1..-1])
                end
            else
                acc = acc.send(arg)
            end
        end
    }
end


p thread_first("a b c d",
               :upcase,
               [:sub, "A", "X"],
               [:split, " "],
               :first)
# => "X"

# no built in lazy sequences, so cheating a bit with a fixed range
p thread_first(0..100,
               :to_a,
               [:map, proc {|i| i*i}],
               [:select, proc {|i| i.even?}],
               [:take, 10],
               [:reduce, :+])
# => 1140

person = {
  :name => "Mark Volkmann",
  :address => {
    :street => "644 Glen Summit",
    :city => "St. Charles",
    :state => "Missouri",
    :zip => 63304
  },
  :employer => {
    :name => "Object Computing, Inc.",
    :address => {
      :street => "12140 Woodcrest Executive Drive, Suite 250",
      :city => "Creve Coeur",
      :state => "Missouri",
      :zip => 63141
    }
  }
}

p thread_first(person, :employer, :address, :city)
# => "Creve Coeur"