add debugging macro to unstable

svn: r17534

collects/unstable/debug.ss

@@ -0,0 +1,18 @@
+#lang scheme/base
+
+(provide debug)
+
+;; printf debugging convenience
+(define-syntax debug
+  (syntax-rules ()
+    [(_ (f . args))
+     (begin (printf "starting ~a~n" 'f)
+            (let ([l (list . args)])
+              (printf "arguments are:~n")
+              (for/list ([arg 'args]
+                         [val l])
+                (printf "\t~a: ~a~n" arg val))
+              (let ([e (apply f l)])
+                (printf "result was ~a~n" e)
+                e)))]
+    [(_ f . args) (debug (f . args))]))

collects/unstable/scribblings/debug.scrbl

@@ -0,0 +1,25 @@
+#lang scribble/doc
+@(require scribble/base
+          scribble/manual scribble/eval
+          "utils.ss"
+          (for-label unstable/debug
+                     scheme/serialize
+                     scheme/contract
+                     scheme/base))
+
+@title[#:tag "debug"]{Debugging}
+@(define the-eval (make-base-eval))
+@(the-eval '(require unstable/debug))
+
+@defmodule[unstable/debug]
+
+@unstable-header[]
+
+@defform*[[(debug (f args ...))
+          (debug f args ...)]]{
+Produce debugging output for the application of @scheme[f], including the values of @scheme[args].
+@examples[#:eval the-eval
+(debug (+ 3 4 (* 5 6)))
+(debug + 1 2 3)
+]
+}