% % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % %
%                                                                           %
% File:            xx2.dtr                                                  %
% Purpose:         a recognizer for XX languages                            %
% Author:          Gerald Gazdar, March 1994                                %
% Email:           geraldg@cogs.sussex.ac.uk                                %
% Address:         COGS, Sussex University, Brighton BN1 9QH, UK            %
% Related files:   mix1.dtr, mix2.dtr, anbncn.dtr, xx1.dtr                  %
% Version:         1.00                                                     %
%                                                                           %
%      Copyright (c) University of Sussex 1994.  All rights reserved.       %
%                                                                           %
% % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % %

% Idem is a function that maps paths to sequences that are identical unless
% an atom outside the set {a, b, c, |} is encountered, in which case that
% atom itself and all the subsequent atoms are deleted.  If the atom is 'fail'
% then the path is mapped to 'fail'.

# vars $idem : a b c |.

Idem:
        <> ==
        <fail> == fail
        <$idem> == $idem <>.

% % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % %

# vars $abc : a b c .

# vars $abc1: a b c 1 .

XX2:    <> == ABC*:<CENTER:<COUNT:<> | Idem:<> ! >>.

COUNT:  <> ==
        <$abc> == fail
        <$abc $abc1> ==  1 <>.

CENTER: <> == Idem:<>
        <fail> == fail
        <1> == <TRANSPOSE:<> !>.

TRANSPOSE:
        <> == fail
        <$abc1> == $abc1 TRANSPOSE:<>
        <| $abc> == $abc | Idem:<>.

ABC:
        <> == fail
        <a> == <a ->
        <b> == <b ->
        <c> == <c ->
        <$abc -> == fail
        <a - $abc> == $abc <a ->
        <b - $abc> == $abc <b ->
        <c - $abc> == $abc <c ->
        <a - | a> == | Idem:<>
        <b - | b> == | Idem:<>
        <c - | c> == | Idem:<>.

ABC*:
        <|> == true
        <fail> == fail
        <> == <ABC:<>>.
        
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# hide Idem COUNT CENTER TRANSPOSE ABC ABC*.

# show  <a a>
        <a b>
        <a b a>
        <a b a b>
        <a b a c>
        <a b c a c>
        <a b c a b c>
        <b b c b b c>
        <b b c a b c>
        <b a b c a b c>
        <b a b c b a b c>.

% The next line is the Revision Control System Id: do not delete it.
% $Id: archive.dtr,v 1.1 1997/04/09 20:40:33 root Exp $