Replace a let loop with a for loop

parser-tools/private-yacc/input-file-parser.rkt

@@ -217,12 +217,9 @@
           nt
           p
           #f
-          (let loop ([i (sub1 (vector-length p))])
+          (for/first ([gs (in-vector p (sub1 (vector-length p)) -1 -1)]
-            (and (>= i 0)
+                      #:when (term? gs))
-                 (let ([gs (vector-ref p i)])
+            (term-prec gs))
-                   (if (term? gs)
-                       (term-prec gs)
-                       (loop (sub1 i))))))
           (parse-action #'PROD-RHS #'ACTION)))]
       [(PROD-RHS (PREC TERM) ACTION)
        (identifier? #'TERM)