adjust hole structs to print better while still

preserving proper equality

fix 1384d2d277

pkgs/redex/private/lang-struct.rkt

@@ -14,16 +14,23 @@
 (define-struct rhs (pattern) #:transparent)
 (define-values (the-hole the-not-hole hole?)
   (let ()
-    (define-struct hole ()
+    (struct hole (which)
-      #:property prop:equal+hash (list (λ (x y recur) #t) (λ (v recur) 255) (λ (v recur) 65535))
+      #:property prop:equal+hash (list (λ (x y recur) #t)
+                                       (λ (v recur) 255)
+                                       (λ (v recur) 65535))
+      #:methods gen:custom-write
+      [(define (write-proc a-hole port mode)
+         (define str (if (equal? (hole-which a-hole) 'the-hole)
+                         "hole"
+                         "not-hole"))
+         (cond
+           [(or (equal? mode 0) (equal? mode 1))
+            (write-string str port)]
+           [else
+            (write-string "#<" port)
+            (write-string str port)
+            (write-string ">" port)]))]
       #:inspector #f)
-    (define-struct not-hole ()
+    (define the-hole (hole 'the-hole))
-      #:property prop:equal+hash (list (λ (x y recur) #t) (λ (v recur) 254) (λ (v recur) 65534))
+    (define the-not-hole (hole 'the-not-hole))
-      #:inspector #f)
+    (values the-hole the-not-hole hole?)))
-    (define the-hole (make-hole))
-    (define the-not-hole (make-not-hole))
-    (define -hole?
-      (let ([hole?
-             (λ (x) (or (hole? x) (not-hole? x)))])
-        hole?))
-    (values the-hole the-not-hole -hole?)))