Extract operation from string and executes it

calculator.ex

# Sample usage:
#
#   iex(1)> Calculator.calculate('123 + 27')
#   150
#   iex(2)> Calculator.calculate('123 - 27')
#   96
#   iex(3)> Calculator.calculate('123 * 27')
#   3321
#   iex(4)> Calculator.calculate('123 / 27')
#   4.555555555555555
#
defmodule Calculator do
  def calculate(s) when is_list(s) do
    s |> List.to_string() |> calculate()
  end

  def calculate(s) do
    [a, operator, b] = Regex.run(~r/(\d+)\s*(\+|-|\*|\/)\s*(\d+)/, s, capture: :all_but_first)

    a = String.to_integer(a)
    b = String.to_integer(b)
    operator = String.to_atom(operator)

    apply(Kernel, operator, [a, b])
  end
end