Validation

[eluser]schnoodles[/eluser]
Hello i am currently building a usersystem and i am up to the part where you check to see if the username and password is correct. i was wondering if there is a proper way to throw errors for functions to make them look like it was a validation error.

So i could do like

Code:

if ( $validation->run() == true ) {
if ( !$user->exists ) { //do like a validation error }
else {

}
}

Anyone know what the best way to accomplish what i am trying to do is ?