[erlang-questions] How do I elegantly check many conditions?

[ryeguy]

So when a user sends a request to register an account, they send their
username, password, email, and other info. The registration function
must verify all of their data. An example would be:

 - verify email not in use
 - verify username not in use
 - verify username is alphanumeric
 - verify all fields are above X characters long
 - verify all fields are less than Y characters long

Now I don't want to have a 5 level deep if or case statement, but what
other options do I have? Splitting it into separate functions sounds
like a good idea, but then I just have to check the return value of
the functions in some sort of conditional and it's back to the
original problem.

I could separate them into functions and then call an if statement
with all of the conditionals OR'd together, but that wouldn't give me
what I want because I need to be able to tell the user the specific
error if there was one.

How does one handle this kind of situation in erlang?