#!/usr/bin/perl -wT

use strict;
use Parse::RecDescent;

my $parser = new Parse::RecDescent( q{
startrule:             calculation eofile
statement:             grouped_op | number
grouped_op:            '(' calculation ')'
calculation:           add_calculation | subtract_calculation
add_calculation:       statement '+' statement
subtract_calculation:  statement '-' statement
number:                /\d+/
eofile:                /^\Z/
} );

my @tests = (
             "3",                    # BAD
             "4 + ",                 # BAD
             "4 + 8",                # GOOD
	       "4 + 8 +",              # BAD
             "6 + (3 - 2)",          # GOOD
             "6 + ()3 - 2",          # BAD
             "(6 + (3 - 2)) + 1",    # GOOD
             "(6 + (3 - 2) + 1)",    # BAD
             "(6 + 3"                # BAD
             );

foreach my $test ( @tests ) {
     print $test . ': ' .
         ( defined($parser->startrule( $test ) )?"good":"bad") . "\n";
}