….Public libraries don’t track patrons’ housing status, and librarians say there’s no way to tell whether someone lacks housing just by looking at them. But many library regulars in low-income neighborhoods and central cities don’t have a home or a job to go to. Some patrons who lack housing also struggle with mental illness or addiction, and need more than a quiet place to study or read. They might have breakdowns in the reading room, start fights in the lobby or sneak into the bathroom to use drugs…. Public libraries have expanded services in a number of ways. San Francisco was the first to hire a social worker, in 2009. Washington and Denver have followed suit. The Dallas Public Library has used grant money to station two AmeriCorps volunteers behind a help desk — as well as answering questions, they might help proofread resumes or help with food stamp applications — and to hire someone who refers patrons to social services….