Rotating log file with retention

scrbl/simple-log.scrbl

@@ -101,6 +101,34 @@ opened with @racket['replace], and the output is flushed after every line.
 Calling the procedure again replaces the existing file destination.
 }
 
+@defproc[(sl-log-to-rotating-file
+          [filename path-string?]
+          [retention-days exact-positive-integer? 7])
+         void?]{
+
+Registers a daily rotating file destination. The current day's log is kept as
+plain text in @racket[filename]. When the date changes, the previous file is
+compressed with gzip and stored as
+@tt{filename.YYYY-MM-DD.gz}.
+
+@racket[retention-days] is the total number of calendar days retained, including
+the current uncompressed day. With the default value of @racket[7], the current
+day and at most the previous six calendar days are retained. Compressed files
+older than that period are removed.
+
+If @racket[filename] already exists when rotating logging is enabled, a file
+modified today is appended to. An older file is first archived under its last
+modification date. This makes restarting an application on the same day preserve
+the current day's log.
+
+For example:
+
+@racketblock[
+(sl-log-to-rotating-file "application.log")
+(sl-log-to-rotating-file "application.log" 14)
+]
+}
+
 @defproc[(sl-log-to-file&display [filename path-string?]) void?]{
 
 Enables both the display and file destinations.