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

Hynek Vychodil <>
Fri Mar 20 15:17:22 CET 2009


One of Joe's suggestion: program success case code separated from error
handling. You can make it in this way

create_user(Email, UserName, Password) ->
  try
    ok = new_email(Email),
    ok = valid_user_name(UserName),
    ok = new_user(UserName),
    ok = strong_password(Password),
    ...
    _create_user(Email, UserName, Password)
  catch
    error:{badmatch, email_in_use} -> do_something();
    error:{badmatch, invalid_user_name} -> do_something();
    error:{badmatch, user_exists} -> do_something();
    error:{badmatch, weak_password} -> do_something();
    ...
  end.

note that you can do all errors catches out of create_user function which is
better.

create_user(Email, UserName, Password) ->
    ok = new_email(Email),
    ok = valid_user_name(UserName),
    ok = new_user(UserName),
    ok = strong_password(Password),
    ...
    _create_user(Email, UserName, Password).

main() ->
  try
    ...
    some_function_where_create_user_is_called(),
    ...
  catch
    ...
    error:{badmatch, email_in_use} -> do_something();
    error:{badmatch, invalid_user_name} -> do_something();
    error:{badmatch, user_exists} -> do_something();
    error:{badmatch, weak_password} -> do_something();
    ...
  end.

On Fri, Mar 20, 2009 at 2:20 PM, ryeguy <> wrote:

> 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?
> _______________________________________________
> erlang-questions mailing list
> 
> http://www.erlang.org/mailman/listinfo/erlang-questions
>



-- 
--Hynek (Pichi) Vychodil

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