Zrp200/linear1

require "linear1/function"
module Linear1
    class ArithmeticSequence < Function
        def self.find index
            new *(ARGV[index..(ARGV.length - 1)])
        end
        attr_reader :a, :common_difference
        alias d slope
        alias d common_difference
        private :slope, :y_intercept
        alias to_a a
        def initialize *a
            i = 0
            while i < a.length - 2 
                raise ArgumentError, "Elements must have a common difference" unless a[i+1] - a[i] == a[i+2] - a[i+1]
                i += 1
            end
            @common_difference, @a = display_num(a[1]) - display_num(a[0]), a
            super @common_difference, @a[0]
        end
        def to_s # Modified to count from zero instead of one
            "a[n] = #{a[0]} + #{idx d}n"
        end
    end
end