Attempt to make it work without metafunctions, but I think it's going to be difficult to use

test/test-traversal-1.rkt

@@ -1,6 +1,6 @@
 #lang type-expander
 
-(require "../traversal.hl.rkt"
+(require "traversal-util.rkt" ;"../traversal.hl.rkt"
          "ck.rkt")
 
 (define-type Foo (Listof String))

test/test-traversal-2.rkt

@@ -1,6 +1,6 @@
 #lang typed/racket
 
-(require "../traversal.hl.rkt"
+(require "traversal-util.rkt" ;"../traversal.hl.rkt"
          type-expander
          phc-adt
          "ck.rkt"

test/traversal-util.rkt

@@ -0,0 +1,22 @@
+#lang typed/racket
+(require (for-syntax syntax/parse
+                     syntax/parse/experimental/template
+                     type-expander/expander)
+         "../traversal.hl.rkt")
+
+(provide define-fold)
+
+(define-syntax define-fold
+  (syntax-parser
+    [(_ _function-name:id
+        _type-name:id
+        whole-type:type
+        _type-to-replaceᵢ:type ...)
+     (with-folds
+      (λ ()
+        (template
+         (begin
+           (define-type _type-name
+             (∀-replace-in-type whole-type _type-to-replaceᵢ ...))
+           (define _function-name
+             (λ-replace-in-instance whole-type _type-to-replaceᵢ ...))))))]))

traversal.hl.rkt

@@ -389,7 +389,7 @@ where @racket[foldl-map] is defined as:
                 (for-meta 2 phc-toolkit/untyped)
                 (for-meta 2 syntax/parse))
 
-       (provide define-fold
+       (provide with-folds
                 (for-syntax replace-in-instance)
                 (for-syntax replace-in-type))
        <foldl-map>