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5.3.6
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18 Logging

Vincent St-Amour <stamourv@racket-lang.org>

This library is unstable; compatibility will not be maintained. See Unstable: May Change Without Warning for more information.

 (require unstable/logging)

This module provides tools for logging.

procedure

(with-logging-to-port port proc log-spec ...) → any

  port : output-port?
  proc : (-> any)
  log-spec : (or/c 'fatal 'error 'warning 'info 'debug symbol? #f)
Runs proc, outputting any logging that would be received by (make-log-receiver (current-logger) log-spec ...) to port. Returns whatever proc returns.

Example:

> (let ([my-log (open-output-string)])
    (with-logging-to-port my-log
      (lambda ()
        (log-warning "Warning World!")
        (+ 2 2))
      'warning)
    (get-output-string my-log))

"Warning World!\n"

procedure

(with-intercepted-logging interceptor    
  proc    
  log-spec ...) → any
  interceptor : 
(-> (vector/c
      (or/c 'fatal 'error 'warning 'info 'debug)
      string?
      any/c
      (or/c symbol? #f))
     any)
  proc : (-> any)
  log-spec : (or/c 'fatal 'error 'warning 'info 'debug symbol? #f)
Runs proc, calling interceptor on any log message that would be received by (make-log-receiver (current-logger) log-spec ...). interceptor receives the entire log vectors (see Receiving Logged Events) as arguments. Returns whatever proc returns.

Example:

> (let ([warning-counter 0])
    (with-intercepted-logging
      (lambda (l)
        (when (eq? (vector-ref l 0)
                   'warning)
          (set! warning-counter (add1 warning-counter))))
      (lambda ()
        (log-warning "Warning!")
        (log-warning "Warning again!")
        (+ 2 2))
      'warning)
    warning-counter)

2

A lower-level interface to logging is also available.

procedure

(start-recording log-spec ...) → listener?

  log-spec : (or/c 'fatal 'error 'warning 'info 'debug symbol? #f)

procedure

(stop-recording listener)

 → 
(listof (vector/c (or/c 'fatal 'error 'warning 'info 'debug)
                  string?
                  any/c
                  (or/c symbol? #f)))
  listener : listener?
start-recording starts recording log messages matching the given log-spec (see make-log-receiver for how log-spec is interpreted). Messages will be recorded until stopped by passing the returned listener object to stop-recording. stop-recording will then return a list of the log messages that have been reported.

Examples:

(define l (start-recording 'warning))
> (log-warning "1")
> (log-warning "2")
> (stop-recording l)

'(#(warning "1" #<continuation-mark-set> #f)

  #(warning "2" #<continuation-mark-set> #f))

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