%{
=head1 SYNOPSIS

This example illustrates the way the directive C<%tree> works.
Compile it with:

   eyapp -b '' ManualTree.yp 

Run it with:

    ./ManualTree.pm 

=cut

use Data::Dumper;
$Data::Dumper::Indent=1;
sub build_node { 
  my $self = shift;

  my @children = @_;
  my @right = $self->YYRightside();
  my $var = $self->YYLhs;
  my $rule = $self->YYRuleindex();

  for(my $i = 0; $i < @right; $i++) {
    $_ = $right[$i];
    if ($self->YYIsterm($_)) {
      $children[$i] = bless { token => $_, attr => $children[$i] },
                                          __PACKAGE__.'::TERMINAL';
    }
  }
  bless { 
    children => \@children, 
    info => "$var -> @right"
  }, __PACKAGE__."::${var}_$rule" 
}
%}
%right  '='
%left   '-' '+'
%left   '*' '/'
%left   NEG
%defaultaction { build_node(@_) }

%lexer {
    s/^[ \t]+//;

    s/^([0-9]+(?:\.[0-9]+)?)// and return('NUM',$1);
    s/^([A-Za-z][A-Za-z0-9_]*)// and return('VAR',$1);
    s/^(.)//s and return($1,$1);
}

%%
input:                 { } 
        |   input line { }
;

line:     '\n'       { } 
        | exp '\n'   { print Dumper($_[1]);  } 
        | error '\n' { $_[0]->YYErrok; }
;

exp:        NUM    
        |   VAR   
        |   VAR '=' exp         
        |   exp '+' exp         
        |   exp '-' exp        
        |   exp '*' exp       
        |   exp '/' exp      
        |   '-' exp %prec NEG 
        |   '(' exp ')'  { $_[2] } /* Let us simplify a bit the tree */
;

%%

__PACKAGE__->main("exp: ") unless caller();