#

# Calc.yp

# 

# Parse::Yapp input grammar example.

#

# This file is PUBLIC DOMAIN 

#

#

%right  '='

%left   '-' '+'

%left   '*' '/'

%left   NEG

%right  '^'

%%

input:  #empty

        |   input line  { push(@{$_[1]},$_[2]); $_[1] }

;

line:       '\n'                { $_[1] }

        |   exp '\n'            { print "$_[1]\n" }

		|	error '\n' { $_[0]->YYErrok }

;

exp:        NUM

        |   VAR                 { $_[0]->YYData->{VARS}{$_[1]} }

        |   VAR '=' exp         { $_[0]->YYData->{VARS}{$_[1]}=$_[3] }

        |   exp '+' exp         { $_[1] + $_[3] }

        |   exp '-' exp         { $_[1] - $_[3] }

        |   exp '*' exp         { $_[1] * $_[3] }

        |   exp '/' exp         {

                                      $_[3]

                                  and return($_[1] / $_[3]);

                                  $_[0]->YYData->{ERRMSG}

                                    =   "Illegal division by zero.\n";

                                  $_[0]->YYError;

                                  undef

                                }

        |   '-' exp %prec NEG   { -$_[2] }

        |   exp '^' exp         { $_[1] ** $_[3] }

        |   '(' exp ')'         { $_[2] }

;

%%

sub _Error {

        exists $_[0]->YYData->{ERRMSG}

    and do {

        print $_[0]->YYData->{ERRMSG};

        delete $_[0]->YYData->{ERRMSG};

        return;

    };

    print "Syntax error.\n";

}

sub _Lexer {

    my($parser)=shift;

        $parser->YYData->{INPUT}

    or  $parser->YYData->{INPUT} = <STDIN>

    or  return('',undef);

    $parser->YYData->{INPUT}=~s/^[ \t]//;

    for ($parser->YYData->{INPUT}) {

        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);

    }

}

sub Run {

    my($self)=shift;

    $self->YYParse( yylex => \&_Lexer, yyerror => \&_Error );

}

my($calc)=new Calc;

$calc->Run;