A Few FORMAT Recipes

Abstract

Common Lisp’s 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

Of course, most folks realize it’s not worth getting that worked up over anything in a programming language and use it or not without a lot of angst. On the other hand, it’s interesting that these two features are the two features in Common Lisp that implement what are essentially domain-specific languages using a syntax not based on s-expressions. The syntax of FORMAT’s control strings is character based, while the extended LOOP macro can be understood only in terms of the grammar of the LOOP keywords. That one of the common knocks on both FORMAT and LOOP is that they “aren’t Lispy enough” is evidence that Lispers really do like the s-expression syntax.