(define-inline (%length-1 ls) (and (not (null? ls)) (null? (cdr ls))))
(define-inline (%length-1/kind? ls pred) (and (%length-1 ls) (pred (car ls))))

(define-inline (%bkgd-pad-chars)
  (let ((bkgd (current-plotter-bkgd-char)))
    (vector bkgd bkgd bkgd bkgd)) )

(define-inline (%make-dims t b l r) (vector t b l r))
(define-inline (%dims-top dims)     (vector-ref dims 0))
(define-inline (%dims-bottom dims)  (vector-ref dims 1))
(define-inline (%dims-left dims)    (vector-ref dims 2))
(define-inline (%dims-right dims)   (vector-ref dims 3))

(define-inline (%pad-dims? obj)
  (and (vector? obj) (= 4 (vector-length obj))
       (exact-integer? (%dims-top obj))
       (exact-integer? (%dims-bottom obj))
       (exact-integer? (%dims-left obj))
       (exact-integer? (%dims-right obj))) )

(define-inline (%make-chars t b l r) (vector t b l r))
(define-inline (%chars-top chars)     (vector-ref chars 0))
(define-inline (%chars-bottom chars)  (vector-ref chars 1))
(define-inline (%chars-left chars)    (vector-ref chars 2))
(define-inline (%chars-right chars)   (vector-ref chars 3))

(define-inline (%pad-chars? obj)
  (and (vector? obj) (= 4 (vector-length obj))
       (or (not (%chars-top obj)) (char? (%chars-top obj)))
       (or (not (%chars-bottom obj)) (char? (%chars-bottom obj)))
       (or (not (%chars-left obj)) (char? (%chars-left obj)))
       (or (not (%chars-left obj)) (char? (%chars-right obj)))) )

(define-inline (%shape? obj) (procedure? obj))
(define-inline (%shapes? obj) (foldl (lambda (a obj) (and a (%shape? obj))) #t obj))