added current-trace-results

collects/racket/trace.rkt

@@ -4,7 +4,9 @@
          (for-syntax scheme/base))
 
 (provide trace untrace
-         current-trace-print-args trace-call
+         current-trace-print-results
+         current-trace-print-args
+         trace-call
          current-trace-notify
          current-prefix-out current-prefix-in)
 
@@ -108,9 +110,10 @@
   (lambda (name results level)
     (as-trace-notify
      (lambda ()
-       (trace-print-results name results level)))))
+       ((current-trace-print-results) name results level)))))
 
-(define trace-print-results
+(define current-trace-print-results
+  (make-parameter
    (lambda (name results level)
      (let-values (((first rest)
                    (build-prefixes level (current-prefix-out))))
@@ -143,7 +146,7 @@
                               (if n
                                   (string-length rest)
                                   0))))
-             (for-each pretty-print (cdr results)))))))))
+              (for-each pretty-print (cdr results))))))))))
 
 
 ;; A traced-proc struct instance acts like a procedure,

collects/scribblings/reference/trace.scrbl

@@ -92,3 +92,15 @@ ordinary arguments, its keywords, the values of the keywords, and a
 number indicating the depth of the call.
 
 }
+
+@defparam[current-trace-results trace-print-results 
+	  (-> symbol?
+              list? 
+              number?
+              any)]{
+
+The value of this parameter is invoked to print out the results of a
+traced call. It receives the name of the function, the function's
+results, and a number indicating the depth of the call.
+
+}