use strict;
use warnings;
use Text::CSV;

my $csv = Text::CSV->new( { sep_char => "\t" } ); # assuming tab separated input
open my $words, "<", "words.txt" or die "Cannot open words.txt: $!\n";

# the following shows what's in words.txt; it is NOT words.txt itself!
=head words.txt
how			o				B-NP
are			o				I-NP
you			o				I-NP
some		o				o
really	o				B-GP 
=cut

my $lasttype;
my @text;
while( my $row = $csv->getline( $words ) ) {
		my $text = $$row[0];
		my $type = ( $$row[-1] =~ /\w-(\w+)/ ) ? $1 : "";
		$lasttype = $type unless @text; # special treatment for first row
		if( $type eq $lasttype ) {
				push @text, $text;
		} else {
				print '<key="type">'."$lasttype</key><text>@text</text>\n" if $lasttype;
				$lasttype = $type;
				@text = ( $text );
		}
}

# print what's left over when all input read
print '<key="type">'."$lasttype</key><text>@text</text>\n" if $lasttype;

close $words;