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 grammar Expr;

options {
    language = Perl5;
}

@header {
}

@members {
    my %memory;
}

prog:   stat+ ;

stat:   expr NEWLINE { print "$expr.value\n"; }
    |   ID '=' expr NEWLINE
        { $memory{$ID.text} = $expr.value; }
    |   NEWLINE
    ;

expr returns [value]
    :   e=multExpr { $value = $e.value; }
        (   '+' e=multExpr { $value += $e.value; }
        |   '-' e=multExpr { $value -= $e.value; }
        )*
    ;

multExpr returns [value]
    :   e=atom { $value = $e.value; } ('*' e=atom { $value *= $e.value; })*
    ;

atom returns [value]
    :   INT { $value = $INT.text; }
    |   ID
        {
            my $v = $memory{$ID.text};
            if (defined $v) {
                $value = $v;
            } else {
                print STDERR "undefined variable $ID.text\n";
            }
        }
    |   '(' expr ')' { $value = $expr.value; }
    ;

ID  :   ('a'..'z'|'A'..'Z')+ ;
INT :   '0'..'9'+ ;
NEWLINE:'\r'? '\n' ;
WS  :   (' '|'\t')+ { $self->skip(); } ;

#!/usr/bin/perl

use strict;
use warnings;

use blib '../..';

use ANTLR::Runtime::ANTLRStringStream;
use ANTLR::Runtime::CommonTokenStream;
use ExprLexer;
use ExprParser;

my $in;
{
    undef $/;
    $in = <>;
}

my $input = ANTLR::Runtime::ANTLRStringStream->new($in);
my $lexer = ExprLexer->new($input);

my $tokens = ANTLR::Runtime::CommonTokenStream->new({ token_source => $lexer });
my $parser = ExprParser->new($tokens);
$parser->prog();

$ perl t.pl
x=1
y=2
3*(x+y)
^Z
9