
unget(+Stream)

   Back up one character on Stream

Arguments
   +Stream             Integer (stream number) or Atom (reserved or user-defined                symbolic stream name).

Type
   Character I/O

Description
    Go back one character on the given Stream. This can be used to
    implement lookaheads. The number of characters that can be backed
    up is guaranteed to be at least 4.


Resatisfiable
      No.

Fail Conditions
   None

Exceptions
     4 --- Stream is not instantiated.
     5 --- Stream is neither an integer nor an atom.
     6 --- No further backup possible on this stream.

Examples
   
% look ahead one character in Stream:

    peek(Stream, X) :-
    	get(Stream, X),
	unget(Stream).


See Also
   get / 2, get_char / 2
