When called with a variable argument, only the physical stream numbers are returned, not the symbolic aliases.
Success: [eclipse 1]: current_stream(S). S = 0 More? (;) S = 1 More? (;) S = 2 More? (;) S = 3 More? (;) S = 4 More? (;) S = 5 More? (;) no (more) solution. [eclipse 2]: current_stream(output). yes. [eclipse 3]: current_stream(junk). no (more) solution.