<div dir="ltr">Thanks. I understood that Racket starts default receivers, but I didn't understand that when you create a new logger with `define-logger` that it also passes messages to those receivers. But I now see that's the significance of `define-logger` creating a logger that's a "child of (current-logger)".</div><div class="gmail_extra"> <div class="gmail_quote">On Fri, Dec 12, 2014 at 3:27 PM, Matthew Flatt <<a href="mailto:mflatt@cs.utah.edu" target="_blank">mflatt@cs.utah.edu</a>> wrote:<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">By default, Racket starts receivers at 'error to direct logged errors to stderr and syslog. Running your program with racket -W none -L none .... avoids the call to `expensive`. <div class="HOEnZb"><div class="h5"> At Fri, 12 Dec 2014 14:27:24 -0800, Matthew Butterick wrote: > I see that you're right about `log-debug`, but here's the example that led > me to make an incorrect generalization. It seems that the (expensive) > function in `log-test-error` always runs, even if the level is 'none or > 'fatal. I don't understand why. > > #lang racket > > (define-logger test) > > (define current-level (make-parameter #f)) > > (define (activate-test-logger) > (define receiver (make-log-receiver test-logger (current-level))) > (void (thread > (λ () > (let loop () > (match (sync receiver) > [(vector event-level event-message event-value name) > (eprintf (format "[~a] ~a\n" event-level event-message)) > (loop)])))))) > > (define (expensive from) > (displayln (format "expensive op requested from log-test-~a at level ~v" > from (current-level))) > (apply + (range 5000000))) > > (parameterize ([current-level 'none]) > (activate-test-logger) > (log-test-fatal (format "fatal at level ~v" (current-level))) > (log-test-error "error at level ~v = ~a" (current-level) (expensive > "error")) > (log-test-debug "debug at level ~v = ~a" (current-level) (expensive > "debug"))) > > On Fri, Dec 12, 2014 at 1:49 PM, Vincent St-Amour <<a href="mailto:stamourv@ccs.neu.edu">stamourv@ccs.neu.edu</a>> > wrote: > > > > I may be missing something, but `log-debug` and friends already do that. > > > > stamourv@westmount:2014-12-12 16:45:plt$ racket > > Welcome to Racket v6.1.1.6. > > -> (log-debug (begin (displayln "hello!") "log")) > > -> > > stamourv@westmount:2014-12-12 16:45:plt$ racket -W debug > > Welcome to Racket v6.1.1.6. > > GC: 0:min @ 1,356K(+307K)[+160K]; free 932K(-5,028K) 4ms @ 12 > > GC: 0:min @ 1,813K(+3,946K)[+232K]; free 755K(-2,051K) 4ms @ 20 > > GC: 0:min @ 4,040K(+4,087K)[+232K]; free 1,448K(-1,448K) 4ms @ 28 > > GC: 0:min @ 5,015K(+3,112K)[+240K]; free 1,425K(-6,817K) 4ms @ 40 > > GC: 0:min @ 7,459K(+6,060K)[+272K]; free 2,162K(-3,458K) 0ms @ 56 > > GC: 0:min @ 9,356K(+6,211K)[+280K]; free 1,628K(-2,924K) 4ms @ 72 > > GC: 0:min @ 13,230K(+4,353K)[+296K]; free 2,558K(-16,142K) 12ms @ 96 > > GC: 0:min @ 17,224K(+13,943K)[+392K]; free 3,900K(-6,492K) 12ms @ 136 > > GC: 0:min @ 21,878K(+12,457K)[+400K]; free 4,741K(-6,037K) 12ms @ 172 > > GC: 0:min @ 27,016K(+9,255K)[+988K]; free 6,168K(-8,760K) 16ms @ 232 > > GC: 0:min @ 32,548K(+6,315K)[+1,276K]; free 7,665K(-26,641K) 36ms @ 312 > > -> (log-debug (begin (displayln "hello!") "log")) > > hello! > > log > > -> > > > > `log-message`, however, does not. > > > > The problem may be that, when you switch to the lower logging level, > > your old listener for the higher level is still around to receive the > > messages. > > > > Vincent > > > > > > > > At Fri, 12 Dec 2014 13:32:41 -0800, > > Matthew Butterick wrote: > > > > > > Is there a reason not to redefine `log-debug` et al as macros that > > evaluate their arguments lazily? > > > > > > Sort of like this; > > > > > > (if ((current-logging-level) . is-equal-or-above? . 'debug) > > > (log-debug arg ...) > > > (void)) > > > > > > Because I find that my use of these functions often looks like this: > > > > > > (log-debug "Value = ~a" (expensive-operation-for-logging-purposes)) > > > > > > The problem is that when I change to a lower logging level, the > > (expensive-operation) is still evaluated. > > > > > > I asked a similar question about hash-ref! not long ago. The answer was > > that you can get lazy evaluation by wrapping the default argument in a > > lambda, like so: > > > > > > (hash-ref! hashtable key (λ () (expression-that-produces-value))) > > > > > > But it seems there's no equivalent idiom for `log-debug` et al. > > > ____________________ > > > Racket Users list: > > > <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> > > > ____________________ > Racket Users list: > <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> </div></div></blockquote></div></div>