# Day 20
## Exercises
* [x] [RPN Calculator](#rpn-calculator)
### RPN Calculator
[Exercise on Exercism](https://exercism.org/tracks/elixir/exercises/rpn-calculator) **|** [View my solution](https://exercism.org/tracks/elixir/exercises/rpn-calculator/solutions/petros)
#### Solution
Expand to see code (spoiler alert)
{% code lineNumbers="true" %}
```elixir
defmodule RPNCalculator do
@spec calculate!(list(), Function.t()) :: :ok
def calculate!(_stack, operation) do
operation.(1)
end
@spec calculate(list(), Function.t()) :: {:ok, String.t()} | :error
def calculate(_stack, operation) do
try do
operation.(1)
{:ok, "operation completed"}
rescue
_ -> :error
end
end
@spec calculate_verbose(list(), Function.t()) :: {:ok | :error, String.t()}
def calculate_verbose(_stack, operation) do
try do
operation.(1)
{:ok, "operation completed"}
rescue
e in ArgumentError -> {:error, e.message}
end
end
end
```
{% endcode %}
[View gist on GitHub](https://gist.github.com/petros/7cbaacb697de6a52c1931703dd92039e)
#### Notes
I was trying to figure out how to call an anonymous function assigned to a variable when the anonymous functions has no arguments. It's `the_variable.()`. However, it turns out this exercise expects an anonymous function with an arity of 1. But the parameter is not being used. So you can pass anything really: `the_variable.(1)`.
## Overall progress
