For more information including compatibility, examples and test cases, see

1. Logger: (import (robin logger))

The Logger library is used to output messages to an output port. Each message is given a level, and only messages above a certain set level will be output to the port. This allows the developer to control the level of detail output by the program. This logger library uses the same levels as Ruby’s Logger class:

  1. unknown: An unknown message that should always be logged.

  2. fatal: An unhandleable error that results in a program crash.

  3. error: A handleable error condition.

  4. warn: A warning.

  5. info: Generic (useful) information about system operation.

  6. debug: Low-level information for developers.

1.1. new-logger

new-logger creates a new logger object. It accepts one argument: if the argument is a port, the logged output will be directed at that port; if the argument is a string, then the string will be treated as a filename, and the logger will open the file and send output to it.

Use (current-input-port) to set the logger to output to the terminal.

1.2. logger?

logger? checks if the given object is a logger object or not.

1.3. log-close

log-close used to close up the logger. This only has an effect if the logger was created with a string, and has opened its own output file: the file port created by the logger is then closed.

1.4. log-add

log-add is used to output a message. It accepts three arguments:

  • logger is the log object to use for the output

  • msg is the message to output, and must be a string

  • level is the log level to use for the output

Usually you will use one of the functions described in the next subsection, but sometimes it is useful for the program to decide which log level to output a message at.

1.5. log-unknown log-fatal log-error log-warn log-info log-debug

log-unknown log-fatal log-error log-warn log-info log-debug all accept two arguments, the log object and a message to output. The message is output if the log level mentioned in the function name is a valid one given the log object’s current log level.

1.6. log-level

log-level accepts two arguments, a log object and a log level, and sets the logger’s level.

1.7. log-unknown? log-fatal? log-error? log-warn? log-info? log-debug?

log-unknown? log-fatal? log-error? log-warn? log-info? log-debug? all accept one argument, the log object, and return true if a log message at the given level would be output by the log object.

1.8. Example

The following example illustrates how these functions may be used:

(define log (new-logger "log1.txt"))      ; <1>
(log-level log 'info)                     ; <2>
(log-info log "some information logged")  ; <3>
(log-debug log "this will be ignored")    ; <4>
(log-level log 'debug)                    ; <5>
(log-debug log "but this included")       ; <6>
(log-close log)                           ; <7>
  1. Create a new logger, output to the given file

  2. Sets the log level to "info"

  3. Outputs a line at "info" level, which will be output

  4. Tries to output a line at "debug" level, but this will be ignored as it is lower than the set level

  5. Sets the log level to "debug"

  6. And now the log message at "debug" level will be output

  7. Finally, close the logger, which closes the file port it opened

The output from the above example is sent to the file "log1.txt", which contains two lines. Notice the log level precedes each message.

$ more log1.txt
info: some information logged
debug: but this included