nltk.SteppingShiftReduceParser.undo¶

SteppingShiftReduceParser.undo()[source]¶

Return the parser to its state before the most recent shift or reduce operation. Calling undo repeatedly return the parser to successively earlier states. If no shift or reduce operations have been performed, undo will make no changes.

Returns:	true if an operation was successfully undone.
Return type:	bool