Étude 5-1 validation

[MatthewMDavis]

The requirements for Étude 5-1 state:

Your module will ask for the first letter of the shape (in either upper or lower case), then the appropriate dimensions. It should catch invalid letters, non-numeric input, and negative numbers as input. Here is some sample output.

But the code does not appear to catch non-numeric input. :erlang.binary_to_integer throws an error if I enter "five" instead of "5". Indeed, the whole point of Étude 5.2 (regular expressions) seems to be catching non-numeric input.