Use `hash-update!` where possible

parser-tools/private-lex/deriv.rkt

@@ -263,11 +263,7 @@
                                        (set! new-state? #t)
                                        (state new-re (get-state-number))))]
                    [new-all-states (if new-state? (cons new-state all-states) all-states)])
-              (hash-set! transitions 
+              (hash-update! transitions s (λ (v) (cons (cons c new-state) v)) '())
-                         s
-                         (cons (cons c new-state)
-                               (hash-ref transitions s
-                                         '())))
               (cond
                 [new-state?
                  (loop old-states (cons new-state new-states) new-all-states (cdr cs))]

parser-tools/private-yacc/lr0.rkt

@@ -59,7 +59,7 @@
 (define (reverse-assoc assoc)
   (define reverse-hash (make-hash))
   (define (hash-table-add! ht k v)
-    (hash-set! ht k (cons v (hash-ref ht k '()))))
+    (hash-update! ht k (λ (v) (cons v v)) '()))
   (for ([trans-key/kernel (in-list assoc)])
        (define tk (car trans-key/kernel))
        (hash-table-add! reverse-hash