Only canonicalize non (symbol/fixnum/struct-type)s, since these are already unique

prospect/canonicalize.rkt

@@ -8,6 +8,13 @@
 (define sentinel (cons #f #f))
 
 (define (canonicalize val)
+  (cond
+    [(or (struct-type? val)
+         (symbol? val)
+         (fixnum? val))
+     ;; These values already have unique representations.
+     val]
+    [else
      (define b (hash-ref canonical-values
                          val
                          (lambda ()
@@ -17,7 +24,7 @@
      (if (not b)
          (canonicalize val)
          (let ((v (weak-box-value b sentinel)))
-	(if (eq? v sentinel) (canonicalize val) v))))
+           (if (eq? v sentinel) (canonicalize val) v)))]))
 
 (module+ test
   (require rackunit)