; longest line

(define (read-line . port)
  (define (eat p c)
    (if (and (not (eof-object? (peek-char p)))
             (char=? (peek-char p) c))
        (read-char p)))
  (let ((p (if (null? port) (current-input-port) (car port))))
    (let loop ((c (read-char p)) (line '()))
      (cond ((eof-object? c) (if (null? line) c (list->string (reverse line))))
            ((char=? #\newline c) (eat p #\return) (list->string (reverse line)))
            ((char=? #\return c) (eat p #\newline) (list->string (reverse line)))
            (else (loop (read-char p) (cons c line)))))))

(define (longest-line)
  (let loop ((line (read-line)) (max-len 0) (max-line ""))
    (cond ((eof-object? line) max-line)
          ((< max-len (string-length line))
            (loop (read-line) (string-length line) line))
          (else (loop (read-line) max-len max-line)))))

(display (longest-line)) (newline)