Merge pull request #1132 from herbie-fp/fix-derivations

Fix derivation speed broken by #1130

src/core/derivations.rkt

@@ -28,7 +28,7 @@
     [_ altn]))
 
 (define (add-derivations alts)
-  (define cache (make-hasheq))
+  (define cache (make-hash))
   (for/list ([altn (in-list alts)])
     ;; We need to cache this because we'll see the same alt several times
     (alt-map (lambda (altn) (hash-ref! cache altn (lambda () (add-derivations-to altn)))) altn)))