(module pad scheme/base

    ;;; To my knowledge Scheme's (format) function does not allow for
    ;;; specifying field width or alignment.  The functions in this
    ;;; module can be used to pad and align a string destined for
    ;;; (format).

    (provide pad-left
             pad-right)

    (define (pad-left obj n . [(c #\space)])
      "Return the string representation of the object OBJ padded with
character C and left aligned."
      (let* ((s (format "~a" obj))
             (len (string-length s))
             (needed (max 0 (- n len))))
        (string-append s (make-string needed c))))

    (define (pad-right obj n . [(c #\space)])
      "Return the string representation of the object OBJ padded with
character C and right aligned."
      (let* ((s (format "~a" obj))
             (len (string-length s))
             (needed (max 0 (- n len))))
        (string-append (make-string needed c) s)))

)