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=encoding utf8

=head1 NAME

Lucy::Docs::Tutorial::AnalysisTutorial - How to choose and use Analyzers.

=head1 DESCRIPTION

Try swapping out the EasyAnalyzer in our Schema for a
L<StandardTokenizer|Lucy::Analysis::StandardTokenizer>:

    my $tokenizer = Lucy::Analysis::StandardTokenizer->new;
    my $type = Lucy::Plan::FullTextType->new(
        analyzer => $tokenizer,
    );

Search for C<senate>, C<Senate>, and C<Senator> before and after making the
change and re-indexing.

Under EasyAnalyzer, the results are identical for all three searches, but
under StandardTokenizer, searches are case-sensitive, and the result sets for
C<Senate> and C<Senator> are distinct.

=head2 EasyAnalyzer

What’s happening is that L<EasyAnalyzer|Lucy::Analysis::EasyAnalyzer> is performing more aggressive
processing than StandardTokenizer.  In addition to tokenizing, it’s also
converting all text to lower case so that searches are case-insensitive, and
using a “stemming” algorithm to reduce related words to a common stem (C<senat>,
in this case).

EasyAnalyzer is actually multiple Analyzers wrapped up in a single package.
In this case, it’s three-in-one, since specifying a EasyAnalyzer with
C<language =E<gt> 'en'> is equivalent to this snippet creating a
L<PolyAnalyzer|Lucy::Analysis::PolyAnalyzer>:

    my $tokenizer    = Lucy::Analysis::StandardTokenizer->new;
    my $normalizer   = Lucy::Analysis::Normalizer->new;
    my $stemmer      = Lucy::Analysis::SnowballStemmer->new( language => 'en' );
    my $polyanalyzer = Lucy::Analysis::PolyAnalyzer->new(
        analyzers => [ $tokenizer, $normalizer, $stemmer ],
    );

You can add or subtract Analyzers from there if you like.  Try adding a fourth
Analyzer, a SnowballStopFilter for suppressing “stopwords” like “the”, “if”,
and “maybe”.

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

Also, try removing the SnowballStemmer.

    my $polyanalyzer = Lucy::Analysis::PolyAnalyzer->new(
        analyzers => [ $tokenizer, $normalizer ],
    );

The original choice of a stock English EasyAnalyzer probably still yields the
best results for this document collection, but you get the idea: sometimes you
want a different Analyzer.

=head2 When the best Analyzer is no Analyzer

Sometimes you don’t want an Analyzer at all.  That was true for our “url”
field because we didn’t need it to be searchable, but it’s also true for
certain types of searchable fields.  For instance, “category” fields are often
set up to match exactly or not at all, as are fields like “last_name” (because
you may not want to conflate results for “Humphrey” and “Humphries”).

To specify that there should be no analysis performed at all, use StringType:

    my $type = Lucy::Plan::StringType->new;
    $schema->spec_field( name => 'category', type => $type );

=head2 Highlighting up next

In our next tutorial chapter, L<HighlighterTutorial|Lucy::Docs::Tutorial::HighlighterTutorial>,
we’ll add highlighted excerpts from the “content” field to our search results.

