notes.txt

Of course a flood of maps could get overwhelming in a real system,
even if you just turn on this ability for a short while.  We can
capture a random sub-sample of the traced data:

    (p/set-config! 'user :exit-fn
	   '[(policy/random-sample 0.01)
         (select-keys [:fname :return :args]) 
         (sink/memory my-tests)])

We can used a fixed length in-memory queue to keep the last N items

    (def my-tests (sink/make-memory))
    (p/set-config! 'user :exit-fn
	   '[(policy/random-sample 0.01)
         (select-keys [:fname :return :args]) 
         (sink/fixed-memory my-tests 5)])

    (dotimes [i 10]
      (testprobe i 10))

    (clojure.pprint/pprint (seq @my-tests))
    => ({:args (5 10), :return 16, :fname testprobe} 
        {:args (7 10), :return 17, :fname testprobe} 
        {:args (8 10), :return 18, :fname testprobe} 
        {:args (9 10), :return 19, :fname testprobe} 
        {:args (10 10), :return 20, :fname testprobe})

We can also select for specific functions in the namespace:
        
    (p/set-config! 'user :exit-fn
	   '[(policy/select-fn testprobe)
         (select-keys [:fname :return :args]) 
         (sink/memory my-tests)])
    
Or only collect data when there are failures:

    (p/remove-config! 'user :exit-fn)
    (p/set-config! 'user :except-fn
	   '[(select-keys [:ts :fname :return :args])
         sink/console-raw])

    (reset! my-tests (sink/make-memory))

    (defn testprobe [a b] (if (= a 2) (throw (Exception. "oops")) (+ a b 1)))
    (testprobe 1 3)
    => 5
	(testprobe 2 3)
    {:args (2 3), :fname testprobe}
    ; Evaluation aborted.

Finally, what if you just want to write a log in the (almost) traditional way?

    (use '[probe.logging :as log])
    (log/error :msg "This is an error" :exception e :value 10)

This uses the Pedestal convention promoted by Relevance, but captures
the structured data before converting it to a string.  This statement
is equivalent to:

    (probe [:error] :msg "This is an error" :exception e :value 10)

except that the probe statement is only called if the underlying
logger for that namespace is active.