ptr

pitfall/restructure/pointer.rkt

@@ -0,0 +1,20 @@
+#lang br
+
+(define the-ks (make-hash))
+(define xs (make-hash))
+
+(define is '(a b (c . h) d e f g h i j))
+(for ([(v i) (in-indexed is)]
+      #:unless (hash-has-key? xs i))
+  (report* xs i)
+  (hash-set! xs i
+             (let/cc k
+               (let ([v (cond
+                         [(pair? v) (hash-set! the-ks (cdr v) k) (car v)]
+                         [else v])])
+                 (define tk (hash-ref the-ks v #f))
+                 (cond
+                   [tk 
+                    (hash-remove! the-ks v)
+                    (tk (format "~a xref" v))]
+                   [else (format "just ~a" v)])))))