mapfn.rb

class Array
  def mapfn(&proc)
    map do |item|
      lambda do |*args|
        proc.call(*([item] + args))
      end
    end
  end
end

[1, 3, 4, 5].mapfn(&:+).
  map do |adder|
    adder.call(10)
  end.
  tap { |x| puts x.inspect } # => [11, 13, 14, 15]

stringify = Proc.new do |*args|
  args.map(&:to_s).join
end

["A", "B"].mapfn(&stringify).
  map do |prefixer|
    prefixer.call(123, :foo)
  end.
  tap { |x| puts x.inspect } # => ["A123foo", "B123foo"]