> For the complete documentation index, see [llms.txt](https://elixir.petrolidas.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://elixir.petrolidas.com/exhort/day-22.md).
# Day 22
## Exercises
* [ ] [Stack Underflow](#stack-underflow)
### Stack Underflow
[Exercise on Exercism](https://exercism.org/tracks/elixir/exercises/stack-underflow) **|** [View my solution](https://exercism.org/tracks/elixir/exercises/stack-underflow/solutions/petros)
#### Solution
Expand to see code (spoiler alert)
{% code lineNumbers="true" %}
```elixir
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(stack) when length(stack) < 2, do: raise(StackUnderflowError, "when dividing")
def divide([0, _nominator] = _stack), do: raise(DivisionByZeroError)
def divide([divisor, nominator]) when divisor != 0, do: nominator / divisor
end
```
{% endcode %}
[View gist on GitHub](https://gist.github.com/petros/0154390a5bd57a27c963371a36cbc02b)
#### Notes
## Overall progress