What pattern can I employ to return error messages only on failure?

I have a method that performs an XML validation against an XML Schema. If the file is valid, the method returns true. If not, it returns false.

I want to log results of the failed validation. I store the messages in an array, but I can't just return the array as it will evaluate to true also.

It seems sloppy to do this:

results = MyClass.valid_file?(filenaem) if results==true # do something else # log "results" end

I wonder if there is some sort of programming pattern that is a superior solution.