Solution for problem #6 @ http://projecteuler.net/problem=6

6.rb

sum         = ->(num_list) { num_list.reduce(:+) }
square      = ->(number  ) { number * number }
squares     = ->(num_list) { num_list.map {|num| square.(num) } }
sum_squares = ->(num_list) { sum.(squares.(num_list)) }
square_sum  = ->(num_list) { square.(sum.(num_list)) }

gem 'minitest'
require 'minitest/autorun'

describe "sum_squares" do
  it { assert_equal 385, sum_squares.(1..10) }
end

describe "square_sum" do
  it { assert_equal 3025, square_sum.(1..10) }
end

describe "answer to the solution" do
  it { assert_equal 25164150, square_sum.(1..100) - sum_squares.(1..100) }
end