%token NUM = /(\d+)/
%token OP  = /([-+*\/])/

%{
use feature 'state';

my $nxr = 0;

%}

%conflict isInTheMiddle {

  state $nxs = 0;

  $nxs++;

  if ($nxs == $nxr+1) { 
    print "Reducing by :MIDx\n";
    $self->YYSetReduce(['NUM','OP'], ':MIDx' );
    
    $nxr = $nxs = 0; 
  }
  else { $self->YYSetShift('NUM') } 
}

%%
T: preproc S  'other'
;

preproc: /* empty */
   {
     ($nxr) = $_[0]->YYPreParse('ExpList'); 
     warn "Number of x's = $nxr\n";
     $nxr = int ($nxr/2);
   }
;

S:
     x  %PREC isInTheMiddle S x  
  |  %name :MIDx 
     x  %PREC isInTheMiddle 
;

x:
     NUM
  |  x OP NUM
;
%%

=head1 SYNOPSIS

This grammar is similar to the one in file C<nopackrat.eyp>.
It can't be parsed by LR(k) nor LL(k) algorithms.
Backtracking LR and GLR algorithms can but will perform poorly.

Compile it with:

   $ eyapp -TC noPackratPPCR.eyp.eyp

Run it with:

   $ ./noPackratPPCR.pm -t -i -c '2-3 3*4 5+2'

=head1 SEE ALSO

Files C<nopackrat.eyp>, C<noLRk_exp.eyp>, C<noLRk_expSolved.eyp>

=cut