Switch gestalt representations to accommodate n<m filtering.

The previous format separated out the different levels too much.
The new format pushes the level representation *under* the routing
matcher.

minimart/core.rkt

@@ -30,7 +30,9 @@
 	 gestalt-ref
 	 compile-gestalt-projection
 	 gestalt-project
-	 gestalt-project-key-set
+	 matcher-project-level
+	 matcher-project
+	 matcher-key-set
 	 pretty-print-gestalt
 
 	 spawn
@@ -75,10 +77,8 @@
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Protocol and utilities
 
-(define (sub p #:meta-level [ml 0] #:level [l 0])
+(define (sub p #:meta-level [ml 0] #:level [l 0]) (simple-gestalt #f p l ml))
-  (simple-gestalt (pattern->matcher (set #t) p) #f l ml))
+(define (pub p #:meta-level [ml 0] #:level [l 0]) (simple-gestalt #t p l ml))
-(define (pub p #:meta-level [ml 0] #:level [l 0])
-  (simple-gestalt #f (pattern->matcher (set #t) p) l ml))
 
 (define (spawn behavior state [gestalt (gestalt-empty)]) (process gestalt behavior state))
 (define (send body #:meta-level [ml 0]) (message body ml #f))
@@ -191,13 +191,8 @@
 
 (define (update-aggregate-gestalt w pid old-g new-g)
   (struct-copy world w [aggregate-gestalt
-			(gestalt-union (gestalt-combine-straight (world-aggregate-gestalt w)
+			(gestalt-union (gestalt-erase-path (world-aggregate-gestalt w)
-								 old-g
+							   old-g)
-								 (lambda (side x)
-								   (case side
-								     [(left-longer) x]
-								     [(right-longer) '()]))
-								 matcher-erase-path)
 				       new-g)]))
 
 (define (issue-local-routing-update w relevant-gestalt)
@@ -251,14 +246,14 @@
 (define (dispatch-event e w)
   (match e
     [(message body meta-level feedback?)
-     (define matcher (gestalt-ref (world-aggregate-gestalt w) meta-level 0 feedback?))
+     (define matcher (gestalt-ref (world-aggregate-gestalt w) meta-level feedback?))
-     (define pids (matcher-match-value matcher body))
+     (define pids (levels->pids (matcher-match-value matcher body '())))
      (define pt (world-process-table w))
      (for/fold ([w w]) [(pid (in-set pids))]
        (apply-transition pid (deliver-event e pid (hash-ref pt pid)) w))]
     [(routing-update affected-subgestalt)
      (define g (world-aggregate-gestalt w))
-     (define-values (affected-pids uninteresting) (gestalt-match g affected-subgestalt))
+     (define affected-pids (gestalt-match affected-subgestalt g))
      (define pt (world-process-table w))
      (for/fold ([w w]) [(pid (in-set affected-pids))]
        (define p (hash-ref pt pid))

minimart/examples/example-lang.rkt

@@ -3,6 +3,21 @@
 (require (only-in racket/port read-line-evt))
 (require "../drivers/timer.rkt")
 
+(define (quasi-spy e s)
+  (printf "----------------------------------------\n")
+  (printf "QUASI-SPY:\n")
+  (match e
+    [(routing-update g) (pretty-print-gestalt g)]
+    [other
+     (write other)
+     (newline)])
+  (printf "========================================\n")
+  #f)
+(spawn quasi-spy (void) (gestalt-union (sub ? #:level 10 #:meta-level 1)
+				       (pub ? #:level 10 #:meta-level 1)
+				       (sub ? #:level 10)
+				       (pub ? #:level 10)))
+
 (define (r e s)
   (match e
     [(message body _ _) (transition s (send `(print got ,body) #:meta-level 1))]
@@ -32,7 +47,7 @@
     [(routing-update g)
      (printf "EMPTY? ~v\n" (gestalt-empty? g))
      (printf "REF:")
-     (pretty-print-matcher (gestalt-ref g 0 0 #f) #:indent 4)
+     (pretty-print-matcher (gestalt-ref g 0 #f) #:indent 4)
      (printf "INTERSECTED:\n")
      (pretty-print-gestalt (gestalt-filter g (pub (set-timer ? ? ?) #:level 1)))
      #f]

minimart/examples/example-plain.rkt

@@ -5,6 +5,17 @@
 (require "../main.rkt")
 (require "../drivers/timer.rkt")
 
+(define (quasi-spy e s)
+  (printf "----------------------------------------\n")
+  (printf "QUASI-SPY:\n")
+  (match e
+    [(routing-update g) (pretty-print-gestalt g)]
+    [other
+     (write other)
+     (newline)])
+  (printf "========================================\n")
+  #f)
+
 (define (r e s)
   (match e
     [(message body _ _) (transition s (send `(print got ,body) #:meta-level 1))]
@@ -28,7 +39,7 @@
     [(routing-update g)
      (printf "EMPTY? ~v\n" (gestalt-empty? g))
      (printf "REF:")
-     (pretty-print-matcher (gestalt-ref g 0 0 #f) #:indent 4)
+     (pretty-print-matcher (gestalt-ref g 0 #f) #:indent 4)
      (printf "INTERSECTED:\n")
      (pretty-print-gestalt (gestalt-filter g (pub (set-timer ? ? ?) #:level 1)))
      #f]
@@ -46,7 +57,11 @@
      #f]
     [_ #f]))
 
-(run-ground (spawn-timer-driver)
+(run-ground (spawn quasi-spy (void) (gestalt-union (sub ? #:level 10 #:meta-level 1)
+						   (pub ? #:level 10 #:meta-level 1)
+						   (sub ? #:level 10)
+						   (pub ? #:level 10)))
+	    (spawn-timer-driver)
 	    (send (set-timer 'tick 1000 'relative))
 	    (spawn ticker 1 (gestalt-union (pub (set-timer ? ? ?) #:level 1)
 					   (sub (timer-expired 'tick ?))))

minimart/gestalt.rkt

@@ -10,30 +10,35 @@
 	 gestalt-ref
 	 compile-gestalt-projection
 	 gestalt-project
-	 gestalt-project-key-set
+	 matcher-project-level
+	 levels->pids
 	 drop-gestalt
 	 lift-gestalt
 	 simple-gestalt
 	 gestalt-empty
 	 gestalt-empty?
-	 gestalt-combine
-	 gestalt-combine-straight
-	 gestalt-combine-crossed
 	 gestalt-union
 	 gestalt-filter
 	 gestalt-match
+	 gestalt-erase-path
 	 strip-gestalt-label
 	 label-gestalt
 	 pretty-print-gestalt)
 
-;; A Gestalt is a (gestalt (Listof (Listof (Pairof Matcher
+;; A Gestalt is a (gestalt (Listof (Pairof Matcher Matcher))),
-;; Matcher)))), representing the total interests of a process or group
+;; representing the total interests of a process or group of
-;; of processes. The outer list has a present entry for each active
+;; processes. The outer list has a present entry for each active
-;; metalevel, starting with metalevel 0 in the car. The inner lists
+;; metalevel, starting with metalevel 0 in the car. The inner pairs
-;; each have an entry for each active observer level at their
+;; have cars holding matchers representing active subscriptions, and
-;; metalevel. The innermost pairs have cars holding matchers
+;; cdrs representing active advertisements. Each of the Matchers maps
-;; representing active subscriptions, and cdrs representing active
+;; to (Listof (Option (Setof PID))), with the nth entry in the list
-;; advertisements.
+;; corresponding to level n, and #f corresponding to empty-set.
+;;
+;; So,
+;; - metalevels: entries in the outermost list.
+;; - sub/adv: car or cdr of each inner pair, respectively.
+;; - levels: entries in the list at each Matcher success value.
+;;
 ;;
 ;;    "... a few standardised subsystems, identical from citizen to
 ;;     citizen. Two of these were channels for incoming data — one for
@@ -44,8 +49,9 @@
 ;;
 (struct gestalt (metalevels) #:prefab)
 
-;; Convention: A GestaltSet is a Gestalt where all the patterns map to
+;; Convention: A GestaltSet is a Gestalt where all the Matchers map to
-;; #t rather than a PID or any other value.
+;; (Listof (Option #t)) rather than the (Listof (Option (Setof PID)))
+;; described above or any other value.
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
@@ -55,64 +61,78 @@
       ['() (fail-thunk)]
       [(cons x xs) (if (zero? n) x (loop xs (- n 1)))])))
 
+(define (safe-take gcons xs n)
+  (let walk ((xs xs) (n n))
+    (cond [(null? xs) '()]
+	  [(zero? n) '()]
+	  [else (gcons (car xs) (walk (cdr xs) (- n 1)))])))
+
 (define (safe-cdr xs)
   (if (null? xs)
       '()
       (cdr xs)))
 
-(define (gestalt-ref g metalevel level get-advertisements?)
+(define ((guarded-cons unit) a d)
-  (define v (safe-list-ref (gestalt-metalevels g) metalevel (lambda () '())))
+  (if (and (null? d) (equal? a unit))
-  (define p (safe-list-ref v level (lambda () '(#f . #f))))
+      '()
-  ((if get-advertisements? cdr car) p))
+      (cons a d)))
+
+(define cons-level (guarded-cons #f))
+(define cons-metalevel (guarded-cons '(#f . #f)))
+
+;; Gestalt × Natural × Boolean → Matcher
+(define (gestalt-ref g metalevel get-advertisements?)
+  (define v (safe-list-ref (gestalt-metalevels g) metalevel (lambda () '(#f . #f))))
+  ((if get-advertisements? cdr car) v))
 
 (define (compile-gestalt-projection spec)
   (compile-projection spec))
 
-(define (gestalt-project g metalevel level get-advertisements? capture-spec)
+;; Limits the given matcher to only include keys when a subscription
-  (matcher-project (gestalt-ref g metalevel level get-advertisements?) capture-spec))
+;; at *exactly* the given level exists.
+(define (matcher-project-level m level)
+  (matcher-relabel m (lambda (v) (and (safe-list-ref v level (lambda () #f)) #t))))
 
-(define (gestalt-project-key-set g metalevel level get-advertisements? capture-spec)
+(define (gestalt-project g metalevel get-advertisements? capture-spec)
-  (matcher-key-set (gestalt-project g metalevel level get-advertisements? capture-spec)))
+  (matcher-project (gestalt-ref g metalevel get-advertisements?) capture-spec))
+
+(define (levels->pids ls)
+  (foldl (lambda (e acc) (if e (set-union e acc) acc)) (set) ls))
 
 (define (drop-gestalt g)
-  (match-define (gestalt metalevels) g)
+  (gestalt (safe-cdr (gestalt-metalevels g))))
-  (if (null? metalevels) g (gestalt (cdr metalevels))))
 
 (define (lift-gestalt g)
-  (gestalt (cons '#() (gestalt-metalevels g))))
+  (gestalt (cons-metalevel '(#f . #f) (gestalt-metalevels g))))
 
 (define (prepend n x xs)
   (if (zero? n)
       xs
       (cons x (prepend (- n 1) x xs))))
 
-(define (simple-gestalt subs advs level metalevel)
+(define (simple-gestalt is-adv? p level metalevel)
-  (gestalt (prepend metalevel '() (list (prepend level '(#f . #f) (list (cons subs advs)))))))
+  (define m (pattern->matcher (prepend level #f (list #t)) p))
+  (gestalt (prepend metalevel '(#f . #f) (list (if is-adv? (cons #f m) (cons m #f))))))
 
 (define (gestalt-empty) (gestalt '()))
 
 (define (gestalt-empty? g)
-  (andmap (lambda (ls) (andmap (lambda (l) (and (matcher-empty? (car l)) (matcher-empty? (cdr l)))) ls))
+  (andmap (lambda (ml) (and (matcher-empty? (car ml)) (matcher-empty? (cdr ml))))
 	  (gestalt-metalevels g)))
 
-(define (map-zip imbalance-handler item-handler right-unit ls1 ls2)
+(define (map-zip imbalance-handler item-handler gcons ls1 ls2)
   (let walk ((ls1 ls1) (ls2 ls2))
     (match* (ls1 ls2)
       [('() '()) '()]
       [('() ls) (imbalance-handler 'right-longer ls)]
       [(ls '()) (imbalance-handler 'left-longer ls)]
       [((cons l1 ls1) (cons l2 ls2))
-       (define new-item (item-handler l1 l2))
+       (gcons (item-handler l1 l2) (walk ls1 ls2))])))
-       (define new-tail (walk ls1 ls2))
-       (if (and (null? new-tail) (equal? new-item right-unit))
-	   '()
-	   (cons new-item new-tail))])))
 
 (define (gestalt-combine g1 g2 imbalance-handler matcher-pair-combiner)
-  (define (yu ls1 ls2) (map-zip imbalance-handler matcher-pair-combiner '(#f . #f) ls1 ls2))
+  (gestalt (map-zip imbalance-handler matcher-pair-combiner cons-metalevel
-  (define (xu mls1 mls2) (map-zip imbalance-handler yu '() mls1 mls2))
+		    (gestalt-metalevels g1)
-  (gestalt (xu (gestalt-metalevels g1)
+		    (gestalt-metalevels g2))))
-	       (gestalt-metalevels g2))))
 
 (define (gestalt-combine-straight g1 g2 imbalance-handler matcher-combiner)
   (gestalt-combine g1 g2
@@ -128,9 +148,19 @@
 		     (cons (matcher-combiner (car sa1) (cdr sa2))
 			   (matcher-combiner (car sa2) (cdr sa1))))))
 
-(define (gestalt-union1 g1 g2) (gestalt-combine-straight g1 g2
+(define (empty->false s) (if (set-empty? s) #f s))
-							 (lambda (side x) x)
+
-							 matcher-union))
+(define (union-levels m1 m2)
+  (matcher-union m1 m2
+		 #:combine
+		 (lambda (ls1 ls2)
+		   (map-zip (lambda (side x) x)
+			    (lambda (s1 s2) (empty->false (set-union (or s1 (set)) (or s2 (set)))))
+			    cons-level
+			    ls1
+			    ls2))))
+
+(define (gestalt-union1 g1 g2) (gestalt-combine-straight g1 g2 (lambda (side x) x) union-levels))
 
 (define (gestalt-union . gs)
   (if (null? gs)
@@ -140,62 +170,103 @@
 	  [(list g) g]
 	  [(cons g rest) (gestalt-union1 g (walk rest))]))))
 
+(define (filter-levels ls1 ls2)
+  (define r (safe-take cons-level ls1 (- (length ls2) 1)))
+  (if (null? r) #f r))
+(define (filter-matchers m1 m2) (matcher-intersect m1 m2 #:combine filter-levels))
+
 ;; View on g1 from g2's perspective.
 ;; Drops a level from g2 and intersects crossed.
 (define (gestalt-filter g1 g2)
-  (gestalt-combine-crossed g1
+  (gestalt-combine-crossed g1 g2 (lambda (side x) '()) filter-matchers))
-			   (gestalt (map safe-cdr (gestalt-metalevels g2)))
-			   (lambda (side x) '())
-			   (lambda (g1 g2) (matcher-intersect g1 g2
-							      #:combine (lambda (v1 v2) v1)))))
 
+;; Here we want all pids in sets in ls2 such that there are some pids
+;; at lower levels in ls1.
+(define (match-combine-levels ls1 ls2 acc)
+  (let loop ((ls1 ls1) (ls2 ls2))
+    (cond
+     [(null? ls1) acc]
+     [(null? ls2) acc]
+     [(not (car ls1)) (loop (cdr ls1) (cdr ls2))]
+     [else ;; aha! here's a real sub/adv in ls1. The remaining
+	   ;; sub/advs in (cdr ls2) can see it.
+      (levels->pids (cdr ls2))])))
+
+;; Much like gestalt-filter, takes a view on gestalt g1 from g2's
+;; perspective. However, instead of returning the filtered g1, returns
+;; just the set of values in the g2-map that were overlapped by some
+;; part of g1.
 (define (gestalt-match g1 g2)
-  (define (zu sa1 sa2)
+  (let loop ((mls1 (gestalt-metalevels g1))
-    (define-values (a1 a2) (matcher-match-matcher (car sa1) (car sa2)))
+	     (mls2 (gestalt-metalevels g2)))
-    (define-values (d1 d2) (matcher-match-matcher (cdr sa1) (cdr sa2)))
+    (cond [(null? mls1) (set)]
-    (values (set-union a1 d1) (set-union a2 d2)))
+	  [(null? mls2) (set)]
-  (define (mz xs1 xs2 f)
+	  [else (match-define (cons subs1 advs1) (car mls1))
-    (match* (xs1 xs2)
+		(match-define (cons subs2 advs2) (car mls2))
-      [('() xs) (values (set) (set))]
+		(let* ((acc (loop (cdr mls1) (cdr mls2)))
-      [(xs '()) (values (set) (set))]
+		       (acc (matcher-match-matcher subs1 advs2
-      [((cons x1 xs1) (cons x2 xs2))
+						   #:combine match-combine-levels
-       (define-values (r1 r2) (mz xs1 xs2 f))
+						   #:empty acc))
-       (define-values (v1 v2) (f x1 x2))
+		       (acc (matcher-match-matcher advs1 subs2
-       (values (set-union v1 r1) (set-union v2 r2))]))
+						   #:combine match-combine-levels
-  (define (yu ls1 ls2) (mz ls1 ls2 zu))
+						   #:empty acc)))
-  (define (xu mls1 mls2) (mz mls1 mls2 yu))
+		  acc)])))
-  (xu (gestalt-metalevels g1)
+
-      (gestalt-metalevels g2)))
+(define (erase-imbalance-handler side x)
+  (case side
+    [(left-longer) x]
+    [(right-longer) '()]))
+
+(define (erase-levels ls1 ls2)
+  (map-zip erase-imbalance-handler
+	   (lambda (v1 v2) (empty->false (set-subtract (or v1 (set)) (or v2 (set)))))
+	   cons-level
+	   ls1
+	   ls2))
+
+(define (gestalt-erase-path g1 g2)
+  (gestalt-combine-straight g1 g2
+			    erase-imbalance-handler
+			    (lambda (m1 m2) (matcher-erase-path m1 m2 #:combine erase-levels))))
+
+(define ((guarded-map gcons) f xs)
+  (foldr (lambda (e acc) (gcons (f e) acc)) '() xs))
+
+(define map-metalevels (guarded-map cons-metalevel))
 
 (define (gestalt-matcher-transform g f)
-  (define (zu sa) (cons (f (car sa)) (f (cdr sa))))
+  (gestalt (map-metalevels (lambda (p) (cons (f (car p)) (f (cdr p))))
-  (define (yu ls) (map zu ls))
+			   (gestalt-metalevels g))))
-  (define (xu mls) (map yu mls))
-  (gestalt (xu (gestalt-metalevels g))))
 
 (define (strip-gestalt-label g)
-  (gestalt-matcher-transform g (lambda (m) (matcher-relabel m (lambda (old) (set #t))))))
+  (define (xform ls) (map (lambda (l) (and l #t)) ls))
+  (gestalt-matcher-transform g (lambda (m) (matcher-relabel m xform))))
 
 (define (label-gestalt g pid)
-  (gestalt-matcher-transform g (lambda (m) (matcher-relabel m (lambda (old) (set pid))))))
+  (define pidset (set pid))
+  (define (xform ls) (map (lambda (l) (and l pidset)) ls))
+  (gestalt-matcher-transform g (lambda (m) (matcher-relabel m xform))))
 
 (define (pretty-print-gestalt g [port (current-output-port)])
-  (for [(metalevel (in-naturals)) (ls (in-list (gestalt-metalevels g)))]
+  (for [(metalevel (in-naturals)) (p (in-list (gestalt-metalevels g)))]
-    (for [(level (in-naturals)) (l (in-list ls))]
+    (match-define (cons subs advs) p)
-      (match-define (cons subs advs) l)
+    (when (or subs advs)
-      (when (or subs advs)
+      (fprintf port "GESTALT metalevel ~v:\n" metalevel)
-	(fprintf port "GESTALT metalevel ~v level ~v:\n" metalevel level)
+      (when subs (fprintf port "  - subs:") (pretty-print-matcher subs port #:indent 9))
-	(when subs (fprintf port "  - subs:") (pretty-print-matcher subs port #:indent 9))
+      (when advs (fprintf port "  - advs:") (pretty-print-matcher advs port #:indent 9)))))
-	(when advs (fprintf port "  - advs:") (pretty-print-matcher advs port #:indent 9))))))
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (module+ test
   (require rackunit)
 
-  (check-equal? (simple-gestalt 'a 'b 0 0)
+  (check-equal? (gestalt-union (simple-gestalt #f 'a 0 0)
-		(gestalt (list (list (cons 'a 'b)))))
+			       (simple-gestalt #t 'b 0 0))
-  (check-equal? (simple-gestalt 'a 'b 2 2)
+		(gestalt (list (cons (pattern->matcher (list #t) 'a)
-		(gestalt (list '() '() (list '(#f . #f)
+				     (pattern->matcher (list #t) 'b)))))
-					     '(#f . #f)
+  (check-equal? (gestalt-union (simple-gestalt #f 'a 2 2)
-					     (cons 'a 'b))))))
+			       (simple-gestalt #t 'b 2 2))
+		(gestalt (list (cons #f #f)
+			       (cons #f #f)
+			       (cons (pattern->matcher (list #f #f #t) 'a)
+				     (pattern->matcher (list #f #f #t) 'b))))))

minimart/ground.rkt

@@ -16,7 +16,8 @@
 (define event-projection (compile-gestalt-projection (event ?! ?)))
 
 (define (extract-active-events gestalt)
-  (define es (gestalt-project-key-set gestalt 0 0 #f event-projection))
+  (define es
+    (matcher-key-set (matcher-project-level (gestalt-project gestalt 0 #f event-projection) 0)))
   ;; TODO: how should the following error be handled, ideally?
   ;; In principle, security restrictions should make it impossible.
   ;; But absent those, what should be done? Should an offending

minimart/route.rkt

@@ -347,63 +347,57 @@
 		[k (walk rest stack k)])])]))))
 
 (define (matcher-match-matcher re1 re2
-			       #:combine [combine-successes set-union]
+			       #:combine [combine-successes (lambda (v1 v2 a)
-			       #:empty [result-nil (set)])
+							      (cons (set-union (car a) v1)
+								    (set-union (cdr a) v2)))]
+			       #:empty [result-nil (cons (set) (set))])
   (let ()
-    (define (walk re1 re2 acc1 acc2)
+    (define (walk re1 re2 acc)
       (match* (re1 re2)
-	[((wildcard-sequence r1) (wildcard-sequence r2)) (walk r1 r2 acc1 acc2)]
+	[((wildcard-sequence r1) (wildcard-sequence r2)) (walk r1 r2 acc)]
-	[((wildcard-sequence r1) r2) (walk (expand-wildseq r1) r2 acc1 acc2)]
+	[((wildcard-sequence r1) r2) (walk (expand-wildseq r1) r2 acc)]
-	[(r1 (wildcard-sequence r2)) (walk r1 (expand-wildseq r2) acc1 acc2)]
+	[(r1 (wildcard-sequence r2)) (walk r1 (expand-wildseq r2) acc)]
-	[((success v1) (success v2)) (values (combine-successes acc1 v1)
+	[((success v1) (success v2)) (combine-successes v1 v2 acc)]
-					     (combine-successes acc2 v2))]
 	[((? hash? h1) (? hash? h2))
 	 (define w1 (rlookup h1 ?))
 	 (define w2 (rlookup h2 ?))
-	 (define-values (r1 r2) (if (and w1 w2)
+	 (define r (if (and w1 w2)
-				    (walk w1 w2 acc1 acc2)
+		       (walk w1 w2 acc)
-				    (values acc1 acc2)))
+		       acc))
-	 (define (examine-key r1 r2 key)
+	 (define (examine-key r key)
 	   (match* ((rlookup h1 key) (rlookup h2 key))
-	     [(#f #f) (values r1 r2)]
+	     [(#f #f) r]
-	     [(#f k2)
+	     [(#f k2) (walk-wild walk w1 key k2 r)]
-	      (define-values (rr1 rr2) (walk-wild w1 key k2 r1 r2))
+	     [(k1 #f) (walk-wild (lambda (re2 re1 acc) (walk re1 re2 acc)) w2 key k1 r)]
-	      (values rr1 rr2)]
+	     [(k1 k2) (walk k1 k2 r)]))
-	     [(k1 #f)
-	      (define-values (rr2 rr1) (walk-wild w2 key k1 r2 r1))
-	      (values rr1 rr2)]
-	     [(k1 k2) (walk k1 k2 r1 r2)]))
 	 ;; We optimize as described in matcher-intersect.
 	 (match* (w1 w2)
-	   [(#f #f) (for/fold [(r1 r1) (r2 r2)] [(key (in-hash-keys (smaller-hash h1 h2)))]
+	   [(#f #f) (for/fold [(r r)] [(key (in-hash-keys (smaller-hash h1 h2)))] (examine-key r key))]
-		      (examine-key r1 r2 key))]
+	   [(#f _) (for/fold [(r r)] [(key (in-hash-keys h1))] (examine-key r key))]
-	   [(#f _) (for/fold [(r1 r1) (r2 r2)] [(key (in-hash-keys h1))] (examine-key r1 r2 key))]
+	   [(_ #f) (for/fold [(r r)] [(key (in-hash-keys h2))] (examine-key r key))]
-	   [(_ #f) (for/fold [(r1 r1) (r2 r2)] [(key (in-hash-keys h2))] (examine-key r1 r2 key))]
+	   [(_ _) (for/fold [(r r)] [(key (set-remove (set-union (hash-keys h1) (hash-keys h2)) ?))]
-	   [(_ _) (for/fold [(r1 r1) (r2 r2)] [(key (set-remove (set-union (hash-keys h1)
+		    (examine-key r key))])]))
-									   (hash-keys h2))
+    (define (walk-wild walker w key k acc)
-								?))]
-		    (examine-key r1 r2 key))])]))
-    (define (walk-wild w key k acc1 acc2)
       (if w
 	  (cond
-	   [(key-open? key) (walk (rwildseq w) k acc1 acc2)]
+	   [(key-open? key) (walker (rwildseq w) k acc)]
 	   [(key-close? key) (if (wildcard-sequence? w)
-				 (walk (wildcard-sequence-matcher w) k acc1 acc2)
+				 (walker (wildcard-sequence-matcher w) k acc)
-				 (values acc1 acc2))]
+				 acc)]
-	   [else (walk w k acc1 acc2)])
+	   [else (walker w k acc)])
-	  (values acc1 acc2)))
+	  acc))
     (match* (re1 re2)
-      [(#f r) (values result-nil result-nil)]
+      [(#f r) result-nil]
-      [(r #f) (values result-nil result-nil)]
+      [(r #f) result-nil]
-      [(r1 r2) (walk r1 r2 result-nil result-nil)])))
+      [(r1 r2) (walk r1 r2 result-nil)])))
 
 (define (matcher-relabel m f)
   (let walk ((m m))
     (match m
       [#f #f]
-      [(success v) (success (f v))]
+      [(success v) (rsuccess (f v))]
-      [(wildcard-sequence m1) (wildcard-sequence (walk m1))]
+      [(wildcard-sequence m1) (rwildseq (walk m1))]
-      [(? hash?) (for/hash [((k v) (in-hash m))] (values k (walk v)))])))
+      [(? hash?) (for/fold [(acc #f)] [((k v) (in-hash m))] (rupdate acc k (walk v)))])))
 
 (define (compile-projection p)
   ;; Extremely similar to pattern->matcher. Besides use of conses
@@ -928,7 +922,7 @@
 
 (module+ test
   (define (matcher-match-matcher-list m1 m2)
-    (define-values (s1 s2) (matcher-match-matcher m1 m2))
+    (match-define (cons s1 s2) (matcher-match-matcher m1 m2))
     (list s1 s2))
   (let ((abc (foldr matcher-union (matcher-empty)
 		    (list (pattern->matcher SA (list 'a ?))
@@ -940,6 +934,10 @@
 			  (pattern->matcher SD (list 'd ?))))))
     (check-equal? (matcher-match-matcher-list abc abc)
 		  (list (set 'A 'B 'C) (set 'A 'B 'C)))
+    (check-equal? (matcher-match-matcher abc abc
+					 #:combine (lambda (v1 v2 a) (set-union v2 a))
+					 #:empty (set))
+		  (set 'A 'B 'C))
     (check-equal? (matcher-match-matcher-list abc (matcher-relabel bcd (lambda (old) (set #t))))
 		  (list (set 'B 'C) (set #t)))
     (check-equal? (matcher-match-matcher-list abc (pattern->matcher Sfoo ?))