インクリメントとデクリメントで四則演算 with Elixir

calc.exs

defmodule Main do
	def inc x do
		x + 1
	end

	def dec x do
		x - 1
	end

	defp minus(x, y) when x < 0 do
		minus inc(x), inc(y)
	end

	defp minus(x, y) when x > 0 do
		minus dec(x), dec(y)
	end

	defp minus _, y do
		y
	end

	def minus x do
		minus x, 0
	end

	def add x, 0 do
		x
	end

	def add(x, y) when y < 0 do
		minus add minus(x), minus(y)
	end

	def add x, y do
		add inc(x), dec(y)
	end

	def sub x, y do
		add x, minus(y)
	end

	def sum [] do
		0
	end

	def sum [x | xs] do
		add x, sum xs
	end

	def dup _, 0 do
		[]
	end

	def dup x, n do
		[x | dup(x, dec n)]
	end

	def absolute(x) when x < 0 do
		minus x
	end

	def absolute x do
		x
	end

	def times(x, y) when y < 0 do
		times minus(x), minus(y)
	end

	def times x, y do
		sum dup x, y
	end

	def divide(x, y) when x < 0 and y < 0 do
		divide minus(x), minus(y)
	end

	def divide(x, y) when x < 0 or y < 0 do
		minus divide absolute(x), absolute(y)
	end

	def divide(x, y) when x < y do
		0
	end

	def divide x, y do
		inc divide sub(x, y), y
	end
end


IO.puts Main.divide -10, -3