Add access to the failure continuation in match.

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.
+}
+
 
 @; ----------------------------------------
 

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]))
 ))

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)]