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=encoding utf8

=head1 NAME

Lucy::Analysis::SnowballStopFilter - Suppress a “stoplist” of common words.

=head1 SYNOPSIS

    my $stopfilter = Lucy::Analysis::SnowballStopFilter->new(
        language => 'fr',
    );
    my $polyanalyzer = Lucy::Analysis::PolyAnalyzer->new(
        analyzers => [ $tokenizer, $normalizer, $stopfilter, $stemmer ],
    );

=head1 DESCRIPTION

A “stoplist” is collection of “stopwords”: words which are common enough to
be of little value when determining search results.  For example, so many
documents in English contain “the”, “if”, and “maybe” that it may improve
both performance and relevance to block them.

Before filtering stopwords:

    ("i", "am", "the", "walrus")

After filtering stopwords:

    ("walrus")

SnowballStopFilter provides default stoplists for several languages,
courtesy of the L<Snowball project|http://snowball.tartarus.org>, or you may
supply your own.

    |-----------------------|
    | ISO CODE | LANGUAGE   |
    |-----------------------|
    | da       | Danish     |
    | de       | German     |
    | en       | English    |
    | es       | Spanish    |
    | fi       | Finnish    |
    | fr       | French     |
    | hu       | Hungarian  |
    | it       | Italian    |
    | nl       | Dutch      |
    | no       | Norwegian  |
    | pt       | Portuguese |
    | sv       | Swedish    |
    | ru       | Russian    |
    |-----------------------|

=head1 CONSTRUCTORS

=head2 new

    my $stopfilter = Lucy::Analysis::SnowballStopFilter->new(
        language => 'de',
    );
    
    # or...
    my $stopfilter = Lucy::Analysis::SnowballStopFilter->new(
        stoplist => \%stoplist,
    );

Create a new SnowballStopFilter.

=over

=item *

B<stoplist> - A hash with stopwords as the keys.

=item *

B<language> - The ISO code for a supported language.

=back

=head1 METHODS

=head2 transform

    my $inversion = $snowball_stop_filter->transform($inversion);

Take a single L<Inversion|Lucy::Analysis::Inversion> as input
and returns an Inversion, either the same one (presumably transformed
in some way), or a new one.

=over

=item *

B<inversion> - An inversion.

=back

=head1 INHERITANCE

Lucy::Analysis::SnowballStopFilter isa L<Lucy::Analysis::Analyzer> isa Clownfish::Obj.

=cut