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current_stream(?Stream)
Succeeds if Stream is a currently open stream. 
- Stream
- Variable, stream handle, or atom.
Description
   Used to test whether a given identifier or handle denotes an open stream,
   or enumerates all currently open streams on backtracking.
   When called with a variable argument, only stream handles are returned,
   not any symbolic aliases.
Modes and Determinism
- current_stream(+) is semidet
- current_stream(-) is nondet
Fail Conditions
Fails if Stream is instantiated but does not denote an open stream.
Exceptions
- (5) type error 
- Stream is instantiated, but not to an atom or stream handle.
Examples
Success:
    ?- current_stream(S), writeln(S), fail.
    $&(stream,0)
    $&(stream,1)
    $&(stream,2)
    $&(stream,3)
    $&(stream,4)
    $&(stream,5)
    $&(stream,6)
    $&(stream,8)
    No (0.00s cpu)
    ?- current_stream(output).
    Yes (0.00s cpu)
    ?- current_stream(junk).
    No (0.00s cpu)
See Also
open / 3, open / 4, get_stream_info / 3, get_stream / 2