An implementation of a Common Lisp compatible format function. cl-format formats its arguments to an output stream or string based on the format control string given. It supports sophisticated formatting of structured data. Writer is an instance of java.io.Writer, true to output to *out* or nil to output to a string, format-in is the format control string and the remaining arguments are the data to be formatted. The format control string is a string to be output with embedded 'format directives' describing how to format the various arguments passed in. If writer is nil, cl-format returns the formatted result string. Otherwise, cl-format returns nil. For example: (let [results [46 38 22]] (cl-format true "There ~[are~;is~:;are~]~:* ~d result~:p: ~{~d~^, ~}~%" (count results) results)) Prints to *out*: There are 3 results: 46, 38, 22 Detailed documentation on format control strings is available in the "Common Lisp the Language, 2nd edition", Chapter 22 (available online at: http://www.cs.cmu.edu/afs/cs.cmu.edu/project/ai-repository/ai/html/cltl/clm/node200.html#SECTION002633000000000000000) and in the Common Lisp HyperSpec at http://www.lispworks.com/documentation/HyperSpec/Body/22_c.htm