all_your_base

elixir/all-your-base/lib/all_your_base.ex

@@ -0,0 +1,31 @@
+defmodule AllYourBase do
+  @doc """
+  Given a number in input base, represented as a sequence of digits, converts it to output base,
+  or returns an error tuple if either of the bases are less than 2
+  """
+
+  @spec convert(list, integer, integer) :: {:ok, list} | {:error, String.t()}
+  def convert(_digits, input_base, _output_base) when input_base < 2,
+    do: {:error, "input base must be >= 2"}
+
+  def convert(_digits, _input_base, output_base) when output_base < 2,
+    do: {:error, "output base must be >= 2"}
+
+  def convert([0 | digits], input_base, output_base), do: convert(digits, input_base, output_base)
+
+  def convert(digits, input_base, output_base) do
+    unless Enum.all?(digits, &valid_digit?(&1, input_base)) do
+      {:error, "all digits must be >= 0 and < input base"}
+    else
+      result =
+          digits
+          |> Integer.undigits(input_base)
+          |> Integer.digits(output_base)
+
+        {:ok, result}
+    end
+  end
+
+  defp valid_digit?(digit, base) when digit >= 0 and digit < base, do: true
+  defp valid_digit?(_digit, _base), do: false
+end