Finding the Current Input Stream

• current_input(Stream) unifies Stream with the current input stream.
• seeing(S) unifies S with the current input stream. This is exactly the same as current_input(S), except that S will be unified with a filename if the current input stream was opened by see/1 (see ref-iou-sfh-opn).

  seeing/1 can be used to verify that FileNameOrStream is still the current input stream as follows:

            /* nonvar(FileNameOrStream), */
            see(FileNameOrStream),
            ...
            seeing(FileNameOrStream)
            

  If the current input stream has not been changed (or if changed, then restored), the above sequence will succeed for all file names and all stream objects opened by open/[3,4]. However, it will fail for all stream objects opened by see/1 (since only filename access to streams opened by see/1 is supported). This includes the stream object user_input (since the standard input stream is assumed to be opened by see/1, and so seeing/1 would return user in this case).

  seeing/1 can be followed by see/1 to ensure that a section of code leaves the current input unchanged