current_stream(Name, Mode, Stream)

Stream  is  currently  open  stream on name Name in mode Mode where Mode is
either  'read',  'write'  or  'append'.   None  of  the  arguments  need be
initially  instantiated.  This predicate is non-determinate and can be used
to backtrack through all open streams.

The  three  reserved  streams  (user_input,  user_output,  user_error)  are
ignored.

A  fact  of  this form is asserted whenever a stream is created (by open or
process) and retracted whenever a stream is closed.
