From ec77a48d2355d0315f5476ad4d89a72ed696acf6 Mon Sep 17 00:00:00 2001
From: Sam Tobin-Hochstadt <samth@cs.indiana.edu>
Date: Mon, 21 Oct 2013 16:46:59 -0400
Subject: [PATCH] Add access to the failure continuation in `match`.

---
 .../racket-doc/scribblings/reference/match.scrbl       | 10 +++++++++-
 pkgs/racket-pkgs/racket-test/tests/match/examples.rkt  |  8 +++++++-
 racket/collects/racket/match.rkt                       |  7 ++++++-
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/pkgs/racket-pkgs/racket-doc/scribblings/reference/match.scrbl b/pkgs/racket-pkgs/racket-doc/scribblings/reference/match.scrbl
index dfc8aace34..e265a54e1c 100644
--- a/pkgs/racket-pkgs/racket-doc/scribblings/reference/match.scrbl
+++ b/pkgs/racket-pkgs/racket-doc/scribblings/reference/match.scrbl
@@ -34,7 +34,8 @@ arguments.  If this procedure is invoked, it escapes back to the
 pattern matching expression, and resumes the matching process as if
 the pattern had failed to match.  The @racket[body]s must not mutate
 the object being matched before calling the failure procedure,
-otherwise the behavior of matching is unpredictable.
+otherwise the behavior of matching is unpredictable. See also
+@racket[failure-cont].
 
 The grammar of @racket[pat] is as follows, where non-italicized
 identifiers are recognized symbolically (i.e., not by binding).
@@ -518,6 +519,13 @@ b
 A predicate for the exception raised in the case of a match failure.
 }
 
+@defform[(failure-cont)]{
+Continues matching as if the current pattern failed.  Note that unlike
+use of the @racket[=>] form, this does @emph{not} escape the current
+context, and thus should only be used in tail position with respect to
+the @racket[match] form.
+}
+
 
 @; ----------------------------------------
 
diff --git a/pkgs/racket-pkgs/racket-test/tests/match/examples.rkt b/pkgs/racket-pkgs/racket-test/tests/match/examples.rkt
index 42646e5bcc..b1723ad7ce 100644
--- a/pkgs/racket-pkgs/racket-test/tests/match/examples.rkt
+++ b/pkgs/racket-pkgs/racket-test/tests/match/examples.rkt
@@ -710,5 +710,11 @@
            (match-let ([(list x y) (list 1 22)] [(list y z) '(2 3)])
                       (list x y z))))
 
-
+   (comp 1
+         (match (cons 1 2)
+           [(cons a b)
+            (if (< a b)
+                (failure-cont)
+                0)]
+           [_ 1]))
 ))
diff --git a/racket/collects/racket/match.rkt b/racket/collects/racket/match.rkt
index 60c4122df7..d181e5ee31 100644
--- a/racket/collects/racket/match.rkt
+++ b/racket/collects/racket/match.rkt
@@ -1,16 +1,21 @@
 #lang racket/base
-(require racket/match/match
+(require racket/match/match "match/runtime.rkt"
          (for-syntax racket/base))
 (provide (except-out (all-from-out racket/match/match)
                      define-match-expander)
+         failure-cont
          (rename-out [define-match-expander* define-match-expander]))
 
+
 (define-for-syntax (no-old-match-form stx)
   (raise-syntax-error
    #f
    "works only for constructor-based `match' form"
    stx))
 
+(define-syntax-rule (failure-cont) (fail))
+
+
 (define-syntax define-match-expander*
   (syntax-rules ()
     [(_ id expr) (define-match-expander id expr)]