stack-underflow

elixir/stack-underflow/lib/rpn_calculator/exception.ex

@@ -0,0 +1,25 @@
+defmodule RPNCalculator.Exception do
+  defmodule DivisionByZeroError do
+    defexception message: "division by zero occurred"
+  end
+
+  defmodule StackUnderflowError do
+    defexception message: "stack underflow occurred"
+
+    @impl true
+    def exception(value) do
+      case value do
+        [] ->
+          %StackUnderflowError{}
+
+        _ ->
+          %StackUnderflowError{message: "stack underflow occurred, context: " <> value}
+      end
+    end
+  end
+
+  def divide([]), do: raise(StackUnderflowError, "when dividing")
+  def divide([_]), do: raise(StackUnderflowError, "when dividing")
+  def divide([0, _]), do: raise(DivisionByZeroError)
+  def divide([x, y]), do: div(y, x)
+end