Handle Functions

Triggers are coarse filters; they may send you queries you cannot handle. By defining a handle function you can tell your Instant Answer on which triggered search queries to run - or not.

A simple handle function, below, checks if the query remainder has anything in it. If not, it returns undef.

handle remainder => sub {
    return if $_ eq ''; # Explicitly check for the empty string
    return $_;
};

Handle Function Return Values

In a Spice, the handle function returns a value that will be inserted as the parameter to the API call.

In a Goodie, the handle function returns the actual answer.

To stop the Instant Answer from proceeding, a handle function simply returns nothing, e.g. return;

Handle Function Handlers

A handle function takes a handler - a pre-packaged part of the query - that it can use to determine whether the Instant Answer should run or not.

When you choose a handler, you're choosing which input to pass to your handle function. For example, passing query_lc means that query_lc is passed as the input to the function so the value of query_lc (a string) is available in $_:

handle query_lc => sub {
    my $lowercased_query = $_;
}

However, words and matches return an array - these values will be available in the default array variable, @_:

handle words => sub {
   my @words_array = @_;
   my $first_word = shift;
};

The available handlers are:

  • remainder - The query without the trigger words, spacing and case are preserved

  • remainder_lc - Like remainder but in lowercase

  • query_raw - Like remainder but with trigger words intact

  • query - Full query normalized with a single space between terms

  • query_lc - Like query but in lowercase

  • query_clean - Like query_lc but with non-alphanumeric characters removed

  • query_nowhitespace - All whitespace removed

  • query_nowhitespace_nodash - All whitespace and hyphens removed

  • matches - Returns an array of captured expression from a regular expression trigger

  • words - Like query_clean but returns an array of the terms split on whitespace

  • query_parts - Like query but returns an array of the terms split on whitespace

  • query_raw_parts - Like query_parts but array contains original whitespace elements

Accessing the Original Query

Inside the handle function you have access to the various attributes of the original query (the DDG::Request instance) in a variable called $req. For example, $req->query, $req->query_lc, $req->query_raw, $req->remainder, and so on.

This can be useful in determining whether your Instant Answer should run. For example, in GoWatchIt.pm, the handle function aborts if the query contains words in a "stop words" array (defined at the top of the file):

    return if grep {$req->query_lc eq $_} @stopwords;

Accessing Location and Language Information

Inside the handle function you also have access to $loc for location data, and $lang for language related attributes. Learn more about these two useful: Language and Location Reference.

Regex Guards in Handle Functions

We much prefer you use trigger words when possible because they are faster on the back end. In some cases however, regular expressions are necessary, e.g., you need to determine whether a query is suitable beyond the trigger words.

In this case we suggest you consider using triggers as much as you can, supplemented with a regex guard in your handle function. A regex guard is a conditional return statement at the very beginning of your handle function.

A good example of this is the Base64 Goodie. In this case we want to trigger on queries with the form "base64 encode/decode \". Here's an excerpt from Base64.pm which shows how this case is handled using a word trigger, with a regex guard:

triggers startend => "base64";

handle remainder => sub {
    return unless $_ =~ /^(encode|decode|)\s*(.*)$/i;

Another example, the Base Goodie's has a return statement paired with an unless right on the first line of its handle function:

handle remainder => sub {
  return unless  /^([0-9]+)\s*(?:(?:in|as)\s+)?(hex|hexadecimal|octal|oct|binary|base\s*([0-9]+))$/;
  ...
}

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