From 290fe066b68def1439d47d9c2b6e2f4dd8672ba2 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Fri, 26 Aug 2011 06:24:34 -0600
Subject: [PATCH] add optional argument to `weak-box-value' and
 `ephemeron-value'

---
 collects/scribblings/reference/memory.scrbl |  8 ++++----
 collects/tests/racket/basic.rktl            |  6 +++---
 collects/tests/racket/will.rktl             | 15 +++++++++++++++
 src/racket/src/list.c                       |  8 ++++----
 4 files changed, 26 insertions(+), 11 deletions(-)

diff --git a/collects/scribblings/reference/memory.scrbl b/collects/scribblings/reference/memory.scrbl
index 7ecabee4b4..6fe042fb71 100644
--- a/collects/scribblings/reference/memory.scrbl
+++ b/collects/scribblings/reference/memory.scrbl
@@ -23,12 +23,12 @@ where the value can be replaced by @racket[#f] (see
 Returns a new weak box that initially contains @racket[v].}
 
 
-@defproc[(weak-box-value [weak-box weak-box?]) any]{
+@defproc[(weak-box-value [weak-box weak-box?] [gced-v any/c #f]) any/c]{
 
 Returns the value contained in @racket[weak-box]. If the garbage
 collector has proven that the previous content value of
 @racket[weak-box] was reachable only through a weak reference, then
-@racket[#f] is returned.}
+@racket[gced-v] (which defaults to @racket[#f]) is returned.}
 
 @defproc[(weak-box? [v any/c]) boolean?]{
 
@@ -82,11 +82,11 @@ Returns a new @tech{ephemeron} whose key is @racket[key] and whose
 value is initially @racket[v].}
 
 
-@defproc[(ephemeron-value [ephemeron ephemeron?]) any]{
+@defproc[(ephemeron-value [ephemeron ephemeron?] [gced-v any/c #f]) any/c]{
 
 Returns the value contained in @racket[ephemeron]. If the garbage
 collector has proven that the key for @racket[ephemeron] is only
-weakly reachable, then the result is @racket[#f].}
+weakly reachable, then the result is @racket[gced-v] (which defaults to @racket[#f]).}
 
 
 @defproc[(ephemeron? [v any/c]) boolean?]{
diff --git a/collects/tests/racket/basic.rktl b/collects/tests/racket/basic.rktl
index b9f75d6254..f9db3be9ed 100644
--- a/collects/tests/racket/basic.rktl
+++ b/collects/tests/racket/basic.rktl
@@ -184,15 +184,15 @@
   (define b (box 5))
   (test 5 unbox b)
   (when set-box!
-	(set-box! b 6)
-	(test 6 unbox b))
+    (set-box! b 6)
+    (test 6 unbox b))
   (test #t box? b)
   (test #f box? 5)
   (arity-test box 1 1)
   (arity-test unbox 1 1)
   (arity-test box? 1 1)
   (when set-box!
-	(arity-test set-box! 2 2))
+    (arity-test set-box! 2 2))
   (err/rt-test (unbox 8))
   (when set-box!
     (err/rt-test (set-box! 8 8))))
diff --git a/collects/tests/racket/will.rktl b/collects/tests/racket/will.rktl
index c648e59476..c6ccaee984 100644
--- a/collects/tests/racket/will.rktl
+++ b/collects/tests/racket/will.rktl
@@ -165,6 +165,21 @@
   ;; ensure that `something' is retained:
   (test #t symbol? (list-ref (list something) (random 1))))
      
+;; ----------------------------------------
+;; `weak-box-value' and `ephemeron-value' optional result:
+
+(let ()
+  (define stuff
+    (for/list ([n 100])
+      (cons (make-weak-box (gensym))
+            (make-ephemeron (gensym) 10))))
+  (collect-garbage)
+  (define n (for/fold ([n 0]) ([p stuff])
+              (+ n
+                   (or (weak-box-value (car p) 0) 1)
+                   (or (ephemeron-value (cdr p) 0) 1))))
+  (test #t < n 50))
+     
 ;; ----------------------------------------
 
 (report-errs)
diff --git a/src/racket/src/list.c b/src/racket/src/list.c
index 35d59055d6..be7e3cd2dd 100644
--- a/src/racket/src/list.c
+++ b/src/racket/src/list.c
@@ -641,7 +641,7 @@ scheme_init_list (Scheme_Env *env)
   scheme_add_global_constant("weak-box-value",
 			     scheme_make_immed_prim(weak_box_value,
 						    "weak-box-value",
-						    1, 1),
+						    1, 2),
 			     env);
   scheme_add_global_constant("weak-box?",
 			     scheme_make_folding_prim(weak_boxp,
@@ -657,7 +657,7 @@ scheme_init_list (Scheme_Env *env)
   scheme_add_global_constant("ephemeron-value",
 			     scheme_make_immed_prim(ephemeron_value,
 						    "ephemeron-value",
-						    1, 1),
+						    1, 2),
 			     env);
   scheme_add_global_constant("ephemeron?",
 			     scheme_make_folding_prim(ephemeronp,
@@ -3160,7 +3160,7 @@ static Scheme_Object *weak_box_value(int argc, Scheme_Object *argv[])
 
   o = SCHEME_BOX_VAL(argv[0]);
   if (!o)
-    return scheme_false;
+    return ((argc > 1) ? argv[1] : scheme_false);
   else
     return o;
 }
@@ -3414,7 +3414,7 @@ static Scheme_Object *ephemeron_value(int argc, Scheme_Object **argv)
   v = scheme_ephemeron_value(argv[0]);
 
   if (!v)
-    return scheme_false;
+    return ((argc > 1) ? argv[1] : scheme_false);
   else
     return v;
 }