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-------------------------------------------------------------------------------
--
-- Copyright (C) 2009 Stephe Leake
-- Copyright (C) 2000 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 example is an implementation of Example 4.46 from "Compilers
-- Principles, Techniques, and Tools" by Aho, Sethi, and Ullman (aka: "The
-- Dragon Book"). The example was meant to demonstrate basic LALR(1) parsing.
-- Here we show to to perform LL(n) parsing with it.
-------------------------------------------------------------------------------
with Ada.Text_IO;
with OpenToken.Production.List;
with OpenToken.Production.Parser.LALR;
with OpenToken.Production.Parser;
with OpenToken.Recognizer.Character_Set;
with OpenToken.Recognizer.End_Of_File;
with OpenToken.Recognizer.Keyword;
with OpenToken.Text_Feeder.Text_IO;
with OpenToken.Token.Enumerated.Analyzer;
with OpenToken.Token.Enumerated.List;
with OpenToken.Token.Enumerated.Nonterminal;
package ASU_Example_4_46 is
-- The complete list of tokens, with the terminals listed first.
type Token_IDs is (Asterix_ID, ID_ID, Equals_ID, EOF_ID, Whitespace_ID, S_ID, L_ID, R_ID, S_Prime_ID);
package Master_Token is new OpenToken.Token.Enumerated (Token_IDs);
package Tokenizer is new Master_Token.Analyzer (Whitespace_ID);
package Token_List is new Master_Token.List;
package Nonterminal is new Master_Token.Nonterminal (Token_List);
package Production is new OpenToken.Production (Master_Token, Token_List, Nonterminal);
package Production_List is new Production.List;
package Parser is new Production.Parser (Production_List, Tokenizer);
package LALR_Parser is new Parser.LALR;
Syntax : constant Tokenizer.Syntax :=
(Asterix_ID => Tokenizer.Get (OpenToken.Recognizer.Keyword.Get ("*")),
ID_ID => Tokenizer.Get (OpenToken.Recognizer.Keyword.Get ("id")),
Equals_ID => Tokenizer.Get (OpenToken.Recognizer.Keyword.Get ("=")),
EOF_ID => Tokenizer.Get (OpenToken.Recognizer.End_Of_File.Get),
Whitespace_ID => Tokenizer.Get (OpenToken.Recognizer.Character_Set.Get
(OpenToken.Recognizer.Character_Set.Standard_Whitespace)));
-- Define all tokens, for use in declaring the grammar. Note that
-- these may be constants; the parser stores intermediate results
-- in the non-terminal tokens, but it allocates new tokens for
-- that.
--
-- Terminal tokens
Asterix : constant Master_Token.Class := Master_Token.Get (Asterix_ID);
ID : constant Master_Token.Class := Master_Token.Get (ID_ID);
Equals : constant Master_Token.Class := Master_Token.Get (Equals_ID);
EOF : constant Master_Token.Class := Master_Token.Get (EOF_ID);
-- Non-terminal tokens.
S : constant Nonterminal.Class := Nonterminal.Get (S_ID);
L : constant Nonterminal.Class := Nonterminal.Get (L_ID);
R : constant Nonterminal.Class := Nonterminal.Get (R_ID);
S_Prime : constant Nonterminal.Class := Nonterminal.Get (S_Prime_ID);
-- Allow infix operators for building productions
use type Token_List.Instance;
use type Production.Right_Hand_Side;
use type Production.Instance;
use type Production_List.Instance;
------------------------------------------------------------------------
-- Define the Grammar productions.
--
-- The text in the example in the book looks something like:
--
-- S' -> S
-- S -> L = R | R
-- L -> * R | id
-- R -> L
--
Grammar : constant Production_List.Instance :=
S_Prime <= S & EOF and
S <= L & Equals & R and
S <= R and
L <= Asterix & R + Nonterminal.Synthesize_Self and
L <= ID + Nonterminal.Synthesize_Self and
R <= L;
-- Create a text feeder for our Input_File.
Input_File : aliased Ada.Text_IO.File_Type;
Feeder : aliased OpenToken.Text_Feeder.Text_IO.Instance :=
OpenToken.Text_Feeder.Text_IO.Create (Input_File'Access);
Analyzer : Tokenizer.Instance := Tokenizer.Initialize (Syntax, Feeder'Access);
end ASU_Example_4_46;
|
