How to handle "bad argument in arithmetic expression" error by using guards

guards in with match against the result not the input. So in this case it checks that the result of by_ten first matches {:ok,first} and then runs that against the guard. Put your guard on the function itself to guard against input params. Also make sure to have a by_ten without the guard to return an error.

@jordiee

Thank you. Here is the refined code which gives the desired result:

defmodule Xe do

  def call(input) do
    with {:ok, first} <- by_ten(input),
         {:ok, second} <- by_five(first)
    do
      IO.puts second
    else
      _ ->
        IO.puts "error"
    end
  end

  def by_ten(input) when is_integer(input) do
    {:ok, input * 10} 
  end

  def by_ten(_) do
    {:error} 
  end

  def by_five(input) do
    {:ok, input * 5} 
  end

end

Xe.call("abc")

Any remarks are welcome.

Yep looks good. The only thing I would change and its really preference is when my function is only one line I change it to shorthand syntax…so

def by_ten(_), do: {:error}

but again that is all preference.