ANSI Common Lisp 20 Files 20.1 File System Concepts
20.1.1 Coercion of Streams to Pathnames
A stream associated with a file is either a file stream
or a synonym stream whose target is a stream associated with a file.
Such streams can be used as pathname designators.
Normally, when a stream associated with a file is used as a
pathname designator, it denotes the pathname used to
open the file; this may be, but is not required to be, the
actual name of the file.
Some functions, such as truename and delete-file,
coerce streams to pathnames in a different way that
involves referring to the actual file that is open, which might
or might not be the file whose name was opened originally. Such special
situations are always notated specifically and are not the default.