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-------------------------------------------------------------------------------
--
-- Copyright (C) 2002, 2003, 2009, 2010, 2013 Stephe Leake
-- Copyright (C) 1999 Ted Dennison
--
-- This file is part of the OpenToken package.
--
-- The OpenToken package 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 3, or (at your option)
-- any later version. The OpenToken package 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  distributed with the OpenToken
-- package;  see file GPL.txt.  If not, write to  the Free Software Foundation,
-- 59 Temple Place - Suite 330,  Boston, MA 02111-1307, USA.
--
--  As a special exception, if other files instantiate generics from
--  this unit, or you link this unit with other files to produce an
--  executable, this unit does not by itself cause the resulting
--  executable to be covered by the GNU General Public License. This
--  exception does not however invalidate any other reasons why the
--  executable file might be covered by the GNU Public License.
-----------------------------------------------------------------------------

-----------------------------------------------------------------------------
--  This package provides an implementation of a LALR (Look-Ahead
--  Left-to-right scanning Rightmost-deriving) parser for grammars
--  defined by a production list. This is probably the most popular
--  method due to it being a good trade-off between the amount of
--  grammars handled and the size of its parse table.
-----------------------------------------------------------------------------
with Ada.Containers.Doubly_Linked_Lists;
with OpenToken.Production.Parser.LRk_Item;
generic
   First_State_Index : in Natural;
package OpenToken.Production.Parser.LALR is

   --  No private types; that would make it too hard to write the unit tests

   type State_Index is new Integer range First_State_Index .. Integer'Last;

   type Parse_Action_Verbs is (Shift, Reduce, Accept_It, Error);
   type Parse_Action_Rec (Verb : Parse_Action_Verbs := Shift) is record
      case Verb is
      when Shift =>
         State : State_Index;
      when Reduce | Accept_It =>
         Production : OpenToken.Production.Instance;
         Length     : Natural;
      when Error =>
         null;
      end case;
   end record;

   type Parse_Action_Node;
   type Parse_Action_Node_Ptr is access Parse_Action_Node;

   type Parse_Action_Node is record
      Item : Parse_Action_Rec;
      Next : Parse_Action_Node_Ptr; -- non-null only for conflicts
   end record;

   type Action_Node;
   type Action_Node_Ptr is access Action_Node;

   type Action_Node is record
      Symbol : Tokenizer.Terminal_ID;
      Action : Parse_Action_Node_Ptr;
      Next   : Action_Node_Ptr;
   end record;

   type Reduction_Node;
   type Reduction_Node_Ptr is access Reduction_Node;

   type Reduction_Node is record
      Symbol : Nonterminal_ID;
      State  : State_Index;
      Next   : Reduction_Node_Ptr;
   end record;

   type Parse_State is record
      Action_List    : Action_Node_Ptr;
      Reduction_List : Reduction_Node_Ptr;
   end record;

   procedure Put (State : in Parse_State);

   type Parse_Table is array (State_Index range <>) of Parse_State;

   type Parse_Table_Ptr is access Parse_Table;

   type Instance is new OpenToken.Production.Parser.Instance with record
      Table : Parse_Table_Ptr;
   end record;

   subtype Conflict_Parse_Actions is Parse_Action_Verbs range Shift .. Reduce;
   type Conflict is record
      --  A typical conflict is:
      --
      --  REDUCE/SHIFT in state: 11 on token IS
      --
      --  State numbers change with minor changes in the grammar, so
      --  we identify the state by the LHS of the two productions
      --  involved. We also store the state number for generated
      --  conflicts (not for known conflicts from the input file), for
      --  Text_IO output.
      Action_A    : Conflict_Parse_Actions;
      LHS_A       : Token.Token_ID;
      Action_B    : Conflict_Parse_Actions;
      LHS_B       : Token.Token_ID;
      State_Index : Integer; -- not State_Index (below), so we can use -1 to represent unknown
      On          : Token.Token_ID;
   end record;

   package Conflict_Lists is new Ada.Containers.Doubly_Linked_Lists (Conflict);

   function Generate
     (Grammar                  : in Production_List.Instance;
      Analyzer                 : in Tokenizer.Instance;
      Known_Conflicts          : in Conflict_Lists.List := Conflict_Lists.Empty_List;
      Trace                    : in Boolean             := False;
      Put_Grammar              : in Boolean             := False;
      Ignore_Unused_Tokens     : in Boolean             := False;
      Ignore_Unknown_Conflicts : in Boolean             := False)
     return Instance;
   --  We don't use OpenToken.Trace here; we often want to see a trace
   --  of the parser execution without the parser generation.
   --  Analyzer is copied.
   --
   --  Unless Ignore_Unused_Tokens is True, raise Grammar_Error if
   --  there are unused tokens.
   --
   --  Unless Ignore_Unknown_Conflicts is True, raise Grammar_Error if there
   --  are unknown conflicts.

   overriding procedure Parse (Parser : in out Instance);

   procedure Cleanup (Parser : in out Instance) is null;
   --  Free any resources used by Parser.

   procedure Put_Table (Parser : in Instance);

   ----------
   --  Visible for unit test

   package LRk is new OpenToken.Production.Parser.LRk_Item (1);

   procedure Fill_In_Lookaheads
     (Grammar              : in     Production_List.Instance;
      Has_Empty_Production : in     LRk.Nonterminal_ID_Set;
      First                : in     LRk.Derivation_Matrix;
      Kernels              : in out LRk.Item_Set_List;
      Accept_Index         : in     Integer;
      Used_Tokens          : in out Tokenizer.Token_Array_Boolean;
      Trace                : in     Boolean);

   procedure Add_Actions
     (Kernel               : in     LRk.Item_Set_Ptr;
      Accept_Index         : in     Integer;
      Grammar              : in     Production_List.Instance;
      Has_Empty_Production : in     LRk.Nonterminal_ID_Set;
      First                : in     LRk.Derivation_Matrix;
      Conflicts            : in out Conflict_Lists.List;
      Table                : in out Parse_Table;
      Trace                : in     Boolean);

end OpenToken.Production.Parser.LALR;