#!/usr/bin/perl
use warnings;
use strict;
use Data::Dumper;
$Data::Dumper::Terse=1;

my $precedence_perlop=[
  qr/(?:\/|\*|\%|x)/,
  qr/(?:\+|-|\.)/,
  qr/(?:<=|>=|<|>lt|gt|le|ge)/,
  qr/&/,
  qr/(?:\||\^)/,
  qr/&&/,
  qr/(?:\|\||\/\/)/,
  qr/(not)/,
  qr/(and)/,
  qr/(or|xor)/
];

sub parse{
  my ($regex,$input)=@_;
  $input=~s/\s//g;
  for(reverse @$regex){
    if($input=~m/(.+)($_)(.+)/){
      my ($before,$op,$after,$node)=($1,$2,$3);
      $node->{$op}=[parse($regex,$before),parse($regex,$after)];
      return $node;
    }
  }
  return $input;

}

sub evaluate {
  my $tree = shift;
  return $tree unless ref $tree;
  foreach my $op ( keys %{$tree} ) {
    my @terms = map { evaluate($_) } @{ $tree->{$op} };
    my $result;
    eval "\$result = $terms[0] $op $terms[1]";
    return undef if $@;
    return $result;
  }

}

while(<>){
  my $tree = parse($precedence_perlop,$_);
  print Dumper($tree);
  my $ev = evaluate( $tree );
  print "Evaluate to: " . $ev . "\n"
    if defined $ev;
}