How can I check if the parameter a user specifies is one of 3 valid parameters, without using multiple if-then-else statements? I think I need to use $regex, but not sure how to use $regex yet.

What I want to do:

Let's say I have an alias called "check", and "check" allows three different parameters to be specified. How can I check to see if the parameters a user specifies is one of the three valid parameters? I am trying to make this routine small as possible, that's why I prefer not to use multiple if-the-else statements to check the user input.