fmap.rb

require 'binding_of_caller'

module Enumerable

  def my_map(sym)
    [].tap do |r|
      each do |e|
        r << e.send(sym)
      end
    end
  end

  def fmap(sym)
    m = binding.of_caller(1).method(sym)
    [].tap do |r|
      each do |e|
        r << m.(e)
      end
    end
  end

end

if __FILE__ == $0

  def add3(x)
    x + 3
  end

  puts ["hello", "world"].my_map(:upcase)

  puts [1,2].fmap(:add3)
end