%{
=head1 SYNOPSIS

See section 'SOLVING CONFLICTS WITH THE POSTPONED CONFLICT STRATEGY' in
http://search.cpan.org/perldoc?Parse::Eyapp::debuggingtut

This example illustrates how to dynamically
change the behavior of the parser for a shift-reduce conflict
   
Be sure C<DebugTail.pm> is reachable
compile it with 

      eyapp -b '' DynamicallyChangingTheParser.eyp

execute the generated modulino with the option C<-t>:

      ./DynamicallyChangingTheParser.pm -t

=head1 See also

    Debug.eyp Debug1.eyp Debug2.eyp and DebugLookForward.eyp

=cut

our $VERSION = '0.01';

%}

%token D S
%lexer {
    m{\G(\s+)}gc and $self->tokenline($1 =~ tr{\n}{});
    
    return ($1,$1) if m{\G(.)}gc;
}

%tree bypass

# Expect just 1 shift-reduce conflict
%expect 1 

%conflict ISLAST {
        my $self = shift;

        if (${$self->input()} =~ m{(?=\G\s*;\s*S)}) {
          $self->YYSetReduce(';', 'D1' )
        }
        else {
          $self->YYSetShift(';')
        }
      }


%%
p: %name PROG
    block +
;

block:
    %name BLOCK_DS
    '{' ds ';' ss '}' 
  | %name BLOCK_S
    '{' ss '}'
;

ds:
    %name D2
    D                     %PREC ISLAST 
      ';' ds    
  | %name D1
    D                     %PREC ISLAST        
;

ss:
    %name S2
    S ';' ss      
  | %name S1
    S       
;

%%

my $prompt = 'Provide a statement like "{D; S} {D; D; S}" and press <CR><CTRL-D>: ';
__PACKAGE__->main($prompt) unless caller;