stream—a stream associated with a file.
length—a non-negative integer or
file-length returns the length of stream,
nil if the length cannot be determined.
For a binary file, the length is measured in units of the element type of the stream.
(with-open-file (s "decimal-digits.text" :direction :output :if-exists :error) (princ "0123456789" s) (truename s)) → #P"A:>Joe>decimal-digits.text.1" (with-open-file (s "decimal-digits.text") (file-length s)) → 10
Should signal an error of type
type-error if stream is not a stream associated with a file.