moge.rb

require 'rspec'

def cloop(*params, &block)
  r = ->(*xs){ block.(r, *xs) }
  r.(*params)
end

def map(xs, &block)
  cloop([], xs){ |r, nxs, x|
    if x == []
      nxs
    else
      r.(nxs << block.(x.first), x[1..-1])
    end
  }
end

describe 'cloop' do
  before(:all) do
    @xs_orig = [*1..5]
    @xs = @xs_orig.dup
  end

  context 'run map' do
    subject { map(@xs) { |n| n + 10 } }
    it { should == @xs_orig.map { |n| n + 10 } }
  end

  context 'check original array' do
    subject { @xs }
    it { should == @xs_orig }
  end
end