Logv is a cognitively lightweight logging utility for Common Lisp

The most useful form is LOGV, a macro that behaves like PROGN except that it writes each form and its return value to the log.

The following code:

(logv (+ 1 (logv (+ 1 1)))
      (+ 10 10)
      (* 64 64))

will return 4096 and might write something like the following lines to the log:

; [2009/03/27] [19:15:08] [repl-thread]: (+ 1 1) -> 2
; [2009/03/27] [19:15:08] [repl-thread]: (+ 1 (LOGV (+ 1 1))) -> 3
; [2009/03/27] [19:15:08] [repl-thread]: (+ 10 10) -> 20
; [2009/03/27] [19:15:08] [repl-thread]: (* 64 64) -> 4096

LOGVS is like LOGV but understands multiple return values. FORMAT-LOG lets you write to the log with a format string and arguments (like FORMAT).

The behavior of LOGV and LOGVS is controlled by "log settings". Log settings can be changed or accessed with SETF-able function LOG-SETTING. for example the following code:

(setf (log-setting :log-output) "/path/to/log.txt")

makes LOGV, LOGVS, and FORMAT-LOG write to the log file "log.txt"

If the :LOG-OUTPUT setting is:

• T then things that write to the log write to *STANDARD-OUTPUT*
• NIL then things that normally write to the log don't do anything
• a stream then things that write to the log write to the stream
• a pathname designator (a pathname or a string): then things that write to the log write to the file pointed to by the string/pathname. the file is created if it doesn't already exist. if there are special characters they are encoded in UTF-8

The :LOG-PREFIX-STRING-FACTORY setting is a thunk [unary function] that returns a string to be prepended to the log line.

The macro DEF-LOG-ENV enables you to easily roll your own LOGV/LOGVS/FORMAT-LOG like functions and macros. eg:

(def-log-env :my-log (:logv-macro-name my-logv
                      :logvs-macro-name my-logvs
                      :format-log-function-name my-format-log)
   :log-output "/path/to/log.txt"                         ; optional, defaults to t
   :log-prefix-string-factory #<function (lambda ()...>)> ; optional
)

You can then set the log settings of your new log enviroment by adding another arg to LOG-SETTING:

(setf (log-setting :log-output :my-log) "/path/to/mylog.txt")

BSD. See "license.txt"