%{

=head1 SYNOPSIS

This is an example of a bad grammar design.

There are several sources of ambiguity in this grammar:

=over 2

=item * Statments like 

              NUM NUM NUM

are ambiguous. The following two left-most derivations
exists:

             s =*=> ns ns =*=> NUM NUM ns => NUM NUM NUM
or 

             s =*=> ns ns =*=> NUM ns =*=> NUM NUM NUM
 
the same with phrases like C<ID ID ID>

=item * The empty word can be generated in many ways

        s => empty

or

        s => s ns => s empty => empty

etc.

=back

Compile it with 

            eyapp -b '' typicalrr

The compiler will announce:

   3 shift/reduce conflicts and 3 reduce/reduce conflicts

Study the file C<typicalrr.output>. The 3 reduce/reduce conflicts
occur in state 1:

  State 1:

	$start -> s . $end	(Rule 0)
	s -> s . ws	(Rule 2)
	s -> s . ns	(Rule 3)

	$end	shift, and go to state 3

	$end	[reduce using rule 6 (ws)]
	$end	[reduce using rule 4 (ns)]
	ID	[reduce using rule 6 (ws)]
	NUM	[reduce using rule 6 (ws)]
	$default	reduce using rule 4 (ns)

	ns	go to state 2
	ws	go to state 4

        Rules:
        ------
        0:	$start -> s $end
        1:	s -> /* empty */
        2:	s -> s ws
        3:	s -> s ns
        4:	ns -> /* empty */
        5:	ns -> ns NUM
        6:	ws -> /* empty */
        7:	ws -> ws ID

Execute it with:

   ./typicalrr.pm -d

Try inputs C<4 5>,  C<a b> and C<4 5 a b>.


=head1 SEE ALSO

For a solution to the conflicts
see  correcttypicalrr.eyp and typicalrr_fixed.eyp

=cut

use base q{RRTail}; 

%}
%token ID NUM 

%tree

%%
s:
      /* empty */
    | s ws
    | s ns 
;

ns:
      /* empty */
    | ns NUM 
;

ws:
      /* empty */
    | ws ID 
;

%%

unless (caller()) {
  my $prompt = 'Try inputs "4 5",  "a b" and "4 5 a b"'.
               '(press <CR><CTRL-D> to finish): ';
  __PACKAGE__->main($prompt) 
}