We've wrapped several commonly used functions into useful helpers that can be used by any Goodie Instant Answer. These are implemented as "roles" that can be used adding the following line to your Goodie's Perl module (.pm file):

with 'DDG::GoodieRole::RoleName';

Numbers

Often matching and outputting numbers intelligently is required, for this the NumberStyler role is ideal:

with 'DDG::GoodieRole::NumberStyler';
# get the regex for something that "looks like a number"
my $number_re = number_style_regex();
my $number_string =~ qr/($number_re)/;
​
# get an object that can handle the number
my $styler = number_style_for($number_string);
return unless $styler;  # might not be supported
​
my $perl_number = $styler->for_computation($number_string);
# now you can use $perl_number however you want
​
$perl_number *= 2;
​
# when you're ready for output simply use:
$output = $styler->for_display($perl_number);

To aid with ambiguity number_style_for() can also take an array to parse as a set:

my @numbers = qw(123,450 543.43);
my $styler = number_style_for(@numbers);

Date Parsing

Dates are especially complicated as different cultures use different formats; to this end we have the Date role, a simple usage of which is:

with 'DDG::GoodieRole::Dates';
​
# get the regex for something that "looks like a date string"; this doesn't mean it *is* a valid date
my $datestring_regex = datestring_regex();
my $probable_date = qr/($datestring_regex)/i;
​
# returns a DateTime object or undef if the date is invalid
my $parsed_date = parse_datestring_to_date($probable_date);
return unless $parsed_date;
​
# do something with $parsed_date
$parsed_date->add( days => 1 );
​
# output in the standard format
$output = date_output_string($parsed_date);

To aid in distinguishing ambiguous formats (such as 01/02/2003) multiple strings can be parsed collectively as one format like so:

my @date_strings = qw(01/02/2001 02/13/2002);
​
# by parsing as below, it will understand the user meant 2nd Jan 2001 and 13th Feb 2002
my @date_objects = parse_all_datestrings_to_date(@date_strings);

Also available for use are:

• full_month_regex() - matches full month names, i.e. January

• short_month_regex() - matches short month names. i.e. Feb

• month_regex() - matches either short or full month names

• full_day_of_week_regex() - matches full weekday i.e. Wednesday

• short_day_of_week_regex() - matches short weekday i.e. Thu

• parse_descriptive_datestring_to_date() - Takes a string like "next december" and produces the first of the month

• descriptive_datestring_regex() - matches strings that can be parsed with parse_descriptive_datestring_to_date()

• parse_formatted_datestring_to_date() - Takes a string in a variety of formats which can be recognized as exact dates

• formatted_datestring_regex() - matches strings that can be parsed with parse_formatted_datestring_to_date()

• date_output_string() - Takes a DateTime object (or a string which can be parsed into one) and returns a standard formatted output string or an empty string if it cannot be parsed.

HTML Encoding

In all situations when the query string is output as HTML, it must be encoded; this is important for protection from cross-site scripting attacks. There is a handy helper available for Goodies in the form of:

# simple scalar:
my $safe_to_output = html_enc($query_string);
​
# also takes an array:
my @safe_strings = html_enc(@unsafe_strings);

URI Escaping

It is also possible to URI escape ("percent-encode") strings in accordance with RFC 3986. The Goodie helper works like:

# simple scalar:
my $percent_encoded = uri_esc($uri);
​
# also takes an array:
my @percent_encodings = uri_esc(@uris);