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diff --git a/src/vhdl/iir_chain_handling.ads b/src/vhdl/iir_chain_handling.ads
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+--  Generic package to handle chains.
+--  Copyright (C) 2002, 2003, 2004, 2005 Tristan Gingold
+--
+--  GHDL is free software; you can redistribute it and/or modify it under
+--  the terms of the GNU General Public License as published by the Free
+--  Software Foundation; either version 2, or (at your option) any later
+--  version.
+--
+--  GHDL is distributed in the hope that it will be useful, but WITHOUT ANY
+--  WARRANTY; without even the implied warranty of MERCHANTABILITY or
+--  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+--  for more details.
+--
+--  You should have received a copy of the GNU General Public License
+--  along with GHDL; see the file COPYING.  If not, write to the Free
+--  Software Foundation, 59 Temple Place - Suite 330, Boston, MA
+--  02111-1307, USA.
+with Iirs; use Iirs;
+
+--  The generic package Chain_Handling can be used to build or modify
+--  chains.
+--  The formals are the subprograms to get and set the first element
+--   from the parent.
+generic
+   with function Get_Chain_Start (Parent : Iir) return Iir;
+   with procedure Set_Chain_Start (Parent : Iir; First : Iir);
+package Iir_Chain_Handling is
+
+   --  Building a chain:
+   --  Initialize (set LAST to NULL_IIR).
+   procedure Build_Init (Last : out Iir);
+   --  Set LAST with the last element of the chain.
+   --  This is an initialization for an already built chain.
+   procedure Build_Init (Last : out Iir; Parent : Iir);
+
+   --  Append element EL to the chain, whose parent is PARENT and last
+   --   element LAST.
+   procedure Append (Last : in out Iir; Parent : Iir; El : Iir);
+
+   --  Append a subchain whose first element is ELS to a chain, whose
+   --   parent is PARENT and last element LAST.
+   --   The Parent field of each elements of Els is set to PARENT.
+   --  Note: the Append procedure declared just above is an optimization
+   --   of this subprogram if ELS has no next element.  However, the
+   --   above subprogram does not set the Parent field of EL.
+   procedure Append_Subchain (Last : in out Iir; Parent : Iir; Els : Iir);
+end Iir_Chain_Handling;