anchor.diff:     ```"
     (let* [(lenghts (let* [(out '())]
                       (for i 1 (# xss) 1
  +                      (if (! (list? (nth xss i)))
  +                        (error (.. "not a list: " (pretty (nth xss i))
  +                                   " (it's a " (type (nth xss i)) ")"))
  +                        true)
                         (push-cdr! out (# (nth xss i))))
                       out))
            (out '())]
  
positive.code:               get-idx for gensym -or slice /=
                pretty print error tostring  -and
                unpack debug if # + - >= = ! with
                apply and progn))
  (import base)
  (import lua/table)
  (import type (nil? list? empty? assert-type! exists? falsey? eq?))
  (import lua/math (min max))
  
  (defun car (x)
  
negative.code:    > (map succ '(1 2 3))
     out = (2 3 4)
     ```"
    (let* [(lengths (let* [(out '())]
                      (for i 1 (# xss) 1
                        (if (! (list? (nth xss i)))
                          (error (.. "not a list: " (pretty (nth xss i))
                                     " (it's a " (type (nth xss i)) ")"))
                          true)
                        (push-cdr! out (# (nth xss i))))
                      out))
           (out '())]
      (for i 1 (apply min lengths) 1
        (push-cdr! out (apply fn (nths xss i))))
      out))
  
  