It's definitely easier to deal with when using a debugger. But that brings a question to my mind: Why are there so many debuggers that make inspecting the results of intermediate expressions difficult? I should be able to step through my code at a finer granularity than a statement.

Re: self-documenting, certainly sometimes (I mean, you shouldn't play code golf...), but in this case the code in question was:

    2218         if (!valid_localpart(maddr->user) ||
    2219             !valid_domainpart(maddr->domain)) {
    ....
    2234                 return (0);
    2235         }
    2236
    2237         return (1);

It's not obvious to me what you would name the intermediate booleans that would be more self-documenting than the function names used there.