Verify the size of a file called     input.txt     for a file in the current working directory, and another one in the file system root.




 
(define (file-size filename)
  (call-with-input-file filename (lambda (port)
    (let loop ((c (read-char port))
               (count 0))
      (if (eof-object? c) 
          count
          (loop (read-char port) (+ 1 count)))))))
 
(file-size "input.txt")
(file-size "/input.txt")
 