anchor.diff:                    (not (zerop (length (symbol-name arg))))
                     (equal #\& (aref (symbol-name arg) 0))))
              (valid-flag-sigil-p (arg assume-dash-prefix)
  -             (and (find-if (lambda (c) (not (equal #\- c))) arg)
  +             (and (stringp arg)
  +                  (find-if (lambda (c) (not (equal #\- c))) arg)
                     (or assume-dash-prefix
                         (equal #\- (aref arg 0)))))
              (ensure-unique-variable (variable)
  
positive.code:   (:import-from :shcl/core/fork-exec #:run)
    (:export
     #:define-builtin #:define-special-builtin #:lookup-command
     #:command-error #:wrap-errors #:invoke-command #:shell-lambda)
    (:documentation
     "This package contains functionality related to defining and
  running shell commands."))
  
negative.code:                          (ensure-unique-flag (concatenate 'string "--" (string-downcase (symbol-name arg)))))
                   flag))
                 ((consp arg)
                  (destructuring-bind (variable &rest flag-strings) arg
                    (check-type variable symbol)
                    (ensure-unique-variable variable)
                    (unless flag-strings
                      (error "At least one flag string must be provided"))
                    (dolist (flag-string flag-strings)
                      (unless (valid-flag-sigil-p flag-string nil)
                        (error "Flag argument sigils must be a string, start with -, and contain a character other than -"))
                      (ensure-unique-flag flag-string))
                    (vector-push-extend (coerce arg 'vector) flag)))
                 (t
                  (error "Malformed flag argument, got: ~A" arg))))
             (&option (arg)
  