vbtkit/src/lego/MultiFilter.i3

 Copyright (C) 1992, Digital Equipment Corporation                         
 All rights reserved.                                                      
 See the file COPYRIGHT for a full description.                            
                                                                           
 Last modified on Thu Jun 10 13:48:22 PDT 1993 by meehan 
      modified on Mon Feb  1 00:36:23 PST 1993 by mhb    
      modified on Tue Jun 16 13:08:36 PDT 1992 by muller 
      modified on Fri Mar 27 01:47:38 1992 by steveg

<* PRAGMA LL *>

 The MultiFilter interface defines the functionality that is common
   to all clients of multi-filters; namely, retrieving and changing a
   multi-filter's multi-child.


   A multi-filter is a multi-split with at most one child. Thus,
   you can use the procedures in the MultiSplit interface on a VBT
   that is a multi-filter. The semantics of the MultiSplit procedures
   on a multi-filter should be obvious, with the following exceptions:
   MultiSplit.Move on a multi-filter is a no-op, and MultiSplit.Insert
   on a multi-filter replaces the child, if any. 


INTERFACE MultiFilter;

IMPORT VBT;

TYPE T = VBT.T;

 A MultiFilter.T is a VBT.T with a MultiClass.Filter in its
   property set. 
 The following procedures can accept either a MultiFilter.T
   or a Filter.T as the first argument.  If the first argument
   is not a MultiFilter.T, the procedure just calls the corresponding
   procedure in the Filter interface. 


PROCEDURE Child (v: VBT.T): VBT.T;
<* LL.sup = VBT.mu *>

 Return the child of v, or NIL if there is no child. 

PROCEDURE Replace (v, ch: VBT.T): VBT.T;
<* LL.sup = VBT.mu *>

 Replace v's child by ch and return v's  old child. 
 MultiFilter.Replace is similar to MultiSplit.Replace,
   except that it returns the old multi-child instead of taking
   the old multi-child as an argument, and if ch is NIL it is
   similar to MultiSplit.Delete. 


END MultiFilter.