Here's my solution.
#!perl
use warnings;
use strict;
sub rfindi (&@) {
my $th = $_[0];
for my $i (1 .. @_ - 1) {
&$th($_[@_ - $i]) and
return @_ - $i - 1;
}
return;
}
my @t;
my $e = 0;
while (local $_ = <>) {
while (m(<(/)?(\w+))g) {
my $t = uc $2;
if (!defined($1)) {
push @t, $t;
} else {
if ($t eq $t[-1]) {
pop @t;
} elsif (defined(my $i = rfindi { $_[0] eq $t
+} @t)) {
$e = 1;
warn "unclosed ", join(",", @t[$i + 1
+.. @t - 1]), " tags at ", $t,
" end tag";
delete @t[$i .. @t - 1];
} else {
$e = 1;
warn "closing unopened ", $t, " tag";
}
}
#warn "[$.:$+[0]: @t]\n";
}
}
@t and do {
$e = 1;
warn "unclosed ", join(",", @t), " tags at eof";
};
exit $e;
__END__