anchor.diff:     ```"
     (assert-type! p function)
     (assert-type! xs list)
  -  (cond
  -    [(falsey? acc) (filter p xs '())]
  -    [(nil? xs) (reverse acc)]
  -    [true (if (p (car xs))
  -            (filter p (cdr xs) (cons (car xs) acc))
  -            (filter p (cdr xs) acc))]))
  +  (let* [(out '())]
  +    (for i 1 (# xs) 1
  +      (with (x (nth xs i))
  +        (when (p x) (push-cdr! out x))))
  +    out))
   
   (defun any (p xs)
     "Check for the existence of an element in XS that matches the
  
positive.code: (import base)
  (import lua/table)
  (import type (list? nil? assert-type! exists? falsey? eq?))
  
  (defun car (x)
    "Return the first element present in the list X. This function operates
  
negative.code:    ```"
    (assert-type! f function)
    (assert-type! xs list)
    (let* [(out '())]
      (for i 1 (# xs) 1
        (push-cdr! out (f (nth xs i))))
      out))
  
  (defun filter (p xs)
    "Return the list of elements of XS which match the predicate P.
  
     Example:
  