Infix.eyp.rep

  #%semantic token '*' '='
  %right  '='     
  %left   '-' '+' 
  %left   '*' '/' 
  %left   NEG    
  #%tree 
  %tree  bypass

  %%
  line: 
    sts <%name EXPS + ';'>  
  ;
  sts: 
      %name PRINT 
      PRINT leftvalue
    | exp 
  ;
  exp:
      %name NUM  NUM            
    | %name VAR   VAR         
    | %name ASSIGN leftvalue '=' exp 
    | %name PLUS exp '+' exp    
    | %name MINUS exp '-' exp 
    | %name TIMES  exp '*' exp 
    | %name DIV     exp '/' exp 
    | %no bypass NEG 
    #| %name NEG 
      '-' exp %prec NEG 
    |   '(' exp ')'  
  ;
  leftvalue : %name VAR VAR
  ;
  %%
  my $lineno = 1;

  sub Err {
    my $parser = shift;

    my($token)=$parser->YYCurval;
    my($what)= $token ? "input: '$token'" 
                      : "end of input";
    my @expected = $parser->YYExpect();
    local $" = ', ';
    die << "ERRMSG";
Syntax error near $what (line number $lineno). 
Expected one of these terminals: @expected
ERRMSG
  }

  sub Lex {
    my($parser)=shift; # The parser object

    for ($parser->YYData->{INPUT}) { # Topicalize
      m{\G[ \t]*}gc;
      m{\G\n}gc                      
        and $lineno++;
      m{\G([0-9]+(?:\.[0-9]+)?)}gc   
        and return('NUM',$1);
      m{\Gprint}gc                   
        and return('PRINT', 'PRINT');
      m{\G([A-Za-z_][A-Za-z0-9_]*)}gc 
        and return('VAR',$1);
      m{\G(.)}gc                     
        and return($1,$1);
      return('',undef);
    }
  }