# input : string (sentence)
# output: truncated string at period, question mark or exclamation point
sub strim {
    my ($s, $i) = @_;
    $s =~ s/^\s+$//g;
    return $s unless defined $i;
    if (length $s <= $i) {
      return $s;
    } else {
        while (right(left($s, $i), 2) ne '. ' &&
               right(left($s, $i), 2) ne '? ' &&
               right(left($s, $i), 2) ne '! ') {
            $i--;
            return left($s, $_[1]) if ($i < 1);
        }
        return left($s, $i);
    }
}

# input : string, integer
# output: truncated string
sub left {
    my ($s, $i) = @_;
    return unless defined $s;
    return $s unless defined $i;
    return substr($s, 0, $i);
}

# input : string, integer
# output: truncated string
sub right {
    my ($s, $i) = @_;
    return unless defined $s;
    return $s unless defined $i;
    return substr($s, length($s) - $i, $i);
}