NAME

    Text::Util::Chinese - A collection of subroutines for processing
    Chinese Text

DESCRIPTIONS

    The subroutines provided by this module are for processing Chinese
    text. Conventionally, all input strings are assumed to be
    wide-characters. No `decode_utf8` or `utf8::decode` were done in this
    module. Users of this module should deal with input-decoding first
    before passing values to these subroutines.

    Given the fact that corpus files are usually large, it may be a good
    idea to avoid slurping the entire input stream. Conventionally,
    subroutines in this modules accept "input iterator" as its way to
    receive a small piece of corpus at a time. The "input iterator" is a
    CodeRef that returns a string every time it is called, or undef if
    there are nothing more to be processed. Here's a trivial example to
    open a file as an input iterator:

        sub open_as_iterator {
            my ($path) = @_
            open my $fh, '<', $path;
            return sub {
                my $line = <$fh>;
                return undef unless defined($line);
                return decode_utf8($line);
            }
        }
        
        my $input_iter = open_as_iterator("/data/corpus.txt");

    This $input_iter can be then passed as arguments to different
    subroutines.

EXPORTED SUBROUTINES

    extract_words( $input_iter ) #=> ArrayRef[Str]

      This extracts words from Chinese text. A word in Chinese text is a
      token with N charaters. These N characters is often used together in
      the input and therefore should be a meaningful unit.

      The input parameter is a iterator -- a subroutine that must return a
      string of Chinese text each time it is invoked. Or, when the input is
      exhausted, it must return undef. For example:

          open my $fh, '<', 'book.txt';
          my $words = extract_words(
              sub {
                  my $x = <$fh>;
                  return decode_utf8 $x;
              });

      The type of return value is ArrayRef[Str].

      It is likely that this subroutine returns an empty ArrayRef with no
      contents. It is only useful when the volume of input is a leats a few
      thousands of characters. The more, the better.

    extract_presuf( $input_iter, $output_cb, $opts ) #=> HashRef

      This subroutine extract meaningful tokens that are prefix or suffix
      of input. Comparing to extract_word, it yields extracted tokens
      frequently by calling $output_cb.

      It is used like this:

          my $extracted = extract_presuf(
              \&next_input,
              sub {
                  my ($token, $extracted) = @_;
      
                  ...
              },
              +{
                  threshold => 9,
                  lengths => [ 2,3 ],
              }
          );

      The $output_cb callback is passed two arguments. The first one is the
      new $token that appears more then $threshold times as a prefix and as
      a suffix. The second arguments is a HashRef with keys being the set
      of all extracted tokens. The very same HashRef is also going to be
      the return value of this subroutine.

      The 3rd argument is a HashRef with parameters to the internal
      algorithm. threshold should be an Int, lengths should be an
      ArrayRef[Int] and that constraints the lengths of prefixes and
      suffixes to be extracted.

      The default value for threshold is 9, while the default value for
      lengths is [2,3]

    phrase_iterator( $input_iter ) #=> CodeRef

      This subroutine split input into smallelr phrases. It takes an text
      iterator, and returns another one.

    tokenize_by_script( $text ) #=> Array[ Str ]

      This subroutine split text into tokens, where each token is the same
      writing script.

AUTHORS

    Kang-min Liu <gugod@gugod.org>

LICENCE

    Unlicense https://unlicense.org/

