Use a foldr instead of apply

TODO

@@ -47,7 +47,7 @@ Tier 1:
     - puzzle.scm
     - quicksort.scm
     - ray.scm -  Error: Unable to open file outputs/ray.output. similar issue to above?
-    - read0.scm - Error (line 170, char 25): unable to parse character: x3bb
+    - read0.scm - needs open-input-string
     - read1.scm
     - sboyer.scm
     - scheme.scm - Problem with (macro?) being a primitive and defined in application code

scheme/cyclone/transforms.sld

@@ -981,8 +981,12 @@
 ;; TODO: remove unused locals
 (define (filter-unused-variables asts lib-exports)
   (define (do-filter code)
-    (let ((all-fv (apply      ;; More efficient way to do this?
-                    append    ;; Could use delete-duplicates
+    (let ((all-fv ;(apply      ;; More efficient way to do this?
+                  ;  append    ;; Could use delete-duplicates
+                  (foldr
+                    (lambda (l ls)
+                      (append ls l))
+                   '()
                     (map 
                       (lambda (ast)
                         (if (define? ast)