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--- at:tutorial:appendix [2008/07/10 17:21] – added tvcutsem
+++ at:tutorial:appendix [2008/07/10 17:27] – added tvcutsem
@@ Line 600: / Line 600: @@
 ==== Logging Framework ====
+The module ''/.at.support.logger'' defines a tiny logging framework akin to the well-known [[http://logging.apache.org/log4j|Log4J]] logging framework for Java.
+Here's a typical example of how to use a logger:
+<code>
+import /.at.support.logger;
+def log := makeLogger("my prefix", INFO); // do not log DEBUG
+log("a message", ERROR); // message level is optional and defaults to INFO
+</code>
+The ''makeLogger'' function returns a function which can be used to log messages to an output object. It takes three arguments, all of which are optional: a string to be prefixed to every logged message (default ''""''), a logging level (default ''DEBUG'') and an output object (default ''system'').
+The logging level determines which messages are shown on the output log. The available error levels are: ''NONE'', ''DEBUG'', ''WARNING'', ''INFO'', ''ERROR'' and ''FATAL'' in order of exceeding importance. Hence, a log whose default is ''WARNING'' will not show ''DEBUG''-level messages.
+The output object is an object that understands ''println(string)''. It is used by the logging framework to write its log to the screen, a file, etc.
 ==== Object Inspector ====