Refactoring

unstable/lens/compound.rkt

@@ -1,6 +1,7 @@
 #lang racket
 
-(require lens
+(require fancy-app
+         lens
          unstable/sequence)
 
 (module+ test
@@ -36,15 +37,25 @@
                       first-lens))
 
 
+(define (value-list->hash keys vs)
+  (make-immutable-hash (map cons keys vs)))
+
+(define (split-slice n vs)
+  (define grouped
+    (for/list ([group (in-slice n vs)])
+      group))
+  (define (get-ith i)
+    (map (list-ref _ i) grouped))
+  (build-list n get-ith))
+
+(module+ test
+  (check-equal? (split-slice 3 '(a 1 FOO b 2 BAR c 3 BAZ))
+                '((a b c) (1 2 3) (FOO BAR BAZ))))
+
+
 (define (compound-hash-lens . keys/lenses)
-  (define grouped-keys/lenses
+  (match-define (list keys lenses) (split-slice 2 keys/lenses))
-    (for/list ([key/lens (in-slice 2 keys/lenses)])
-      key/lens))
-  (define keys (map first grouped-keys/lenses))
-  (define lenses (map second grouped-keys/lenses))
   (define list-lens (apply compound-list-lens lenses))
-  (define (value-list->hash keys xs)
-    (make-immutable-hash (map cons keys xs)))
   (define (get target)
     (value-list->hash keys (lens-view list-lens target)))
   (define (set target new-view-hash)