FORMAT function is—along with the extended
LOOP macro—one of the two Common Lisp features that inspires a strong emotional response in a lot of Common Lisp users. Some love it; others hate it.1
FORMAT's fans love it for its great power and concision, while its detractors hate it because of the potential for misuse and its opacity. Complex
FORMAT control strings sometimes bear a suspicious resemblance to line noise, but
FORMAT remains popular with Common Lispers who like to be able to generate little bits of human-readable output without having to clutter their code with lots of output-generating code. While
FORMAT's control strings can be cryptic, at least a single
FORMAT expression doesn't clutter ...