Iterator::Simple(3p)

NAME
Iterator::Simple - Simple iterator and utilities

SYNOPSIS
  use Iterator::Simple;

  sub foo {
    my $max = shift;
    my $i = 0;
    iterator {
      return if $i > $max;
      $i++;
    }
  }

  my $iterator = foo(20); # yields 0,1,2, ..., 19, 20;
  $iterator = imap { $_ + 2 } $iterator; # yields 2,3,4,5, ... ,20,21,22
  $iterator = igrep { $_ % 2 } $iterator; # yields 3,5,7,9, ... ,17,19,21

  # iterable object
  $iterator = iter([qw(foo bar baz)]); # iterator from array ref
  $iterator = iter(IO::File->new($filename)); # iterator from GLOB

  # filters
  $iterator = ichain($itr1, $itr2); # chain iterators;
  $iterator = izip($itr1, $itr2); # zip iterators;
  $iterator = ienumerate $iterator; # add index;

  # general filter
  $iterator = ifilter $iterator, sub {
    return $_ if /^A/;
    return;
  }

  # how to iterate
  while(defined($_ = $iterator->())) {
    print;
  }

  while(defined($_ = $iterator->next)) {
    print;
  }

  while(<iterator>) {
    print;
  }

DESCRIPTION
Iterator::Simple is yet another general-purpose iterator utilities.

Rather simple, but powerful and fast iterator.

FUNCTIONS
Iterator::Simple doesn't export any functions by default. please import them like:

  use Iterator::Simple qw(iter list imap);

For all functions:

  use Iterator::Simple qw(:all);

iterator { CODE }
    Iterator constructor. CODE returns a value on each call, and if it is exhausted, returns undef. Therefore, you cannot yields undefined value as a meaning value. If you want, you could use Iterator module which can do that.

    Generally, you can implement iterator as a closure like:

      use Iterator::Simple qw(iterator);

      sub fibonacci {
        my($s1, $s2, $max) = @_;

        iterator {
          my $rv;
          ($rv, $s1, $s2) = ($s1, $s2, $s1 + $s2);
          return if $rv > $max;
          return $rv;
        }
      }

      my $iterator = fiboacci(1, 1, 1000);

    You can iterate it in several ways:

    •   just call it

          while(defined($_ = $iterator->())) {
            print "$_\n";
          }

    •   "next" method

          while(defined($_ = $iterator->next)) {
            print "$_\n";
          }

    •   <> operator

          while(<$iterator>) {
            print "$_\n";
          }

is_iterator($object)
    If $object is an iterator created by Iterator::Simple, returns true. False otherwise.

iter($object)
    This function auto detects what $object is, and automatically turns it into an iterator. Supported objects are:

    •   Iterator made with Iterator::Simple.

    •   Object that implements "__iter__" method.

    •   Object that overloads '<>' or has "next" method.

    •   Object that overloads '&{}'.(as iterator function.)

    •   Object that overloads '@{}'.(with iarray())

    •   ARRAY reference. (iarray())

    •   CODE reference. (as iterator function.)

    •   GLOB reference.

    •   nothing (iter().) (empty iterator.)

    If it fails to convert, runtime error.

is_iterable($object)
    return true if $object can be converted with iter($object)

list($object)
    This function converts $object into single array referece.

    •   ARRAY reference.

    •   GLOB reference.

    •   Iterator made with Iterator::Simple.

    •   Object that overloads '@{}' operator.

    •   Object that implements '__iter__' method.

    •   Object that overloads '<>' operator or has "next" method.

    •   nothing (i.e. list() returns []);

    If it fails to convert, runtime error.

    Note that after list($iterator), that iterator is not usable any more.

imap { CODE } $iterable
    This is the iterator version of "map". Returns an iterator which yields the value from source iterator modified by CODE.

igrep { CODE } $iterable
    This is the iterator version of "grep". Returns an iterator which yields the value from source iterator only when CODE returns true value.

iflatten $iterable
    When $iterable yields another iterator, iterate it first.

      $subitr = iter([10, 11,12]);
      $source = iter([ 1, 2, $subitr, 4]);

      $flattened = iflatten $source;

      # yields 1, 2, 10, 11, 12, 4.

ifilter $iterable, sub{ CODE }
    This is the combination of imap, igrep, iflatten. it supports modify (imap) , skip (igrep), and inflate (iflatten). but it should be faster than combination of them.

    For example:

      $combination = iflatten
        imap { $_ eq 'baz' ? iter(['whoa', 'who']) : ":$_:" }
        igrep { $_ ne 'bar' }
        iter [ 'foo', 'bar', 'baz', 'fiz' ];

      $itr = iter [ 'foo', 'bar', 'baz', 'fiz' ];
      $filterd = ifilter $itr, sub {
        return if $_ eq 'bar'; #skip
        return iter(['whoa', 'who']) if $_ eq 'baz'; #inflate
        return ":$_:"; # modify
      };

    Both of them will yields ':foo:', 'whoa', 'who', ':fiz:'.

ichain($iterable, $iterable2, ...)
    This function returns an iterator which chains one or more iterators. Iterates each iterables in order as is, until each iterables are exhausted.

    Example:

      $itr1 = iter(['foo', 'bar', 'baz']);
      $itr2 = iter(['hoge', 'hage']);

      $chained = ichain($itr1, $itr2);

      # yields 'foo', 'bar', 'baz', 'hoge', 'hage'.

ienumerate($iterable)
    This function returns an iterator yields like:

      $ary = iter(['foo', 'bar', 'baz', ... ]);

      $iter = ienumerate $ary;

      # yields [0, 'foo'], [1, 'bar'], [2, 'baz'], ...

izip($iterable, $iterable2, ...);
    Accepts one or more iterables, returns an iterator like:

      $animals = iter(['dogs', 'cats', 'pigs']);
      $says = iter(['bowwow', 'mew', 'oink']);

      $zipped = izip($animals, $says);

      # yields ['dogs','bowwow'], ['cats','mew'], ['pigs', 'oink'].

    Note that when one of source iterables is exhausted, zipped iterator will be exhausted also.

islice($iterable, $start, $end, $step)
    Same as islice of itertools in Python. If $end is undef or negative value, it iterates source until it is exhausted. $step defaults to 1. 0 or negative step value is prohibited.

      $iter = iter([0,1,2,3,4,5,6,7,8,9,10,11,12]);

      $sliced = islice($iter, 3, 13, 2);

      # yields 3, 5, 7, 9, 11.

ihead($count, $iterable)
      islice($iterable, 0, $count, 1);

iskip($count, $iterable)
      islice($iterable, $count, undef, 1);

iarray($arrayref);
    Turns array reference into an iterator. Used in iter($arrayref). You do not have to use this function directly, because iter($arrayref) is sufficient.

OO INTERFACE
Iterator used in Iterator::Simple is just a code reference blessed in Iterator::Simple::Iterator. This class implements several method and overloads some operators.

Itrator::Simple::Iterator->new($coderef)
    Just bless $coderef in Iterator::Simple::Iterator and returns it.

$iterator->next
    Call underlying code.

$iterator->__iter__
    Returns self. You don't need to use this.

Overloaded operators.
    •   Read filehandle operator '<>'

        Overloading '<>' makes this possible like:

          print while <$iterator>;

    •   Pipe.. bit_OR? .. No, pipe!

          $iterator | $coderef1 | $coderef2;

        is equivalent to:

          $iterator->filter($coderef1)->filter($coderef2);

        is equivalent to:

          ifilter(ifilter($iterator, $coderef1), $coderef2);

$iterator->filter($coderef)
$iterator->flatten()
$iterator->chain($another, ..)
$iterator->zip($another, ..)
$iterator->enumerate()
$iterator->slice($start, $end, $step)
$iterator->head($count)
$iterator->skip($count)
    For example, $iterator->flatten() is equivalent to "iflatten $iterator".

TIPS
All iterator transformation function calls "iter" function on all source iterables. So you can pass just array reference, GLOB ref, etc.

These examples completely do the right thing:

  imap { $_ + 2 } [1, 2, 3, ... ];
  ienumerate(\*STDIN);

  # DBIx::Class::ResultSet has 'next' method.
  ifilter $dbic_resultset, sub {CODE};

You can implement "__iter__" method on your objects in your application. By doing that, your object will be Iterator::Simple friendly :).

Note that "__iter__" method must return an iterator.

Why Not Iterator.pm
There is another iterator module in CPAN, named Iterator and Iterator::Util made by Eric J. Roode that is great solution. Why yet another iterator module? The answer is *Speed*. You use iterator because you have too many data to manipulate in memory, therefore iterator could be called thousands of times, speed is important.

For this simple example:

  use Iterator::Util qw(iarray imap igrep);

  for(1 .. 100) {
    my $itr = igrep { $_ % 2 } imap { $_ + 2 } iarray([1 .. 1000]);
    my @result;
    while($itr->isnt_exhausted) {
      push @result, $itr->value;
    }
  }

meanwhile:

  use Iterator::Simple qw(iarray imap igrep);

  for(1 .. 100) {
    my $itr = igrep { $_ % 2 } imap { $_ + 2 } iarray([1 .. 1000]);
    my @result;
    while(defined($_ = $itr->())) {
      push @result, $_;
    }
  }

Iterator::Simple is about ten times faster!

That is natural because Iterator::Simple iterator is just a code reference, while Iterator.pm iterator is full featured class instance. But Iterator::Simple is sufficient for usual demands.

One of most downside of Iterator::Simple is, you cannot yields undef value as a meaning value, because Iterator::Simple thinks it as a exhausted sign. If you need to do that, you have to yield something which represents undef value.

Also, Iterator::Simple cannot determine iterator is exhausted until next iteration, while Iterator.pm has 'is(nt)_exhausted' method which is useful in some situation.

AUTHOR
Rintaro Ishizaki <rintaro@cpan.org>

LICENSE
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

SEE ALSO

•   Iterator - Feature rich another iterator class.

•   Iterator::Util - Utilities which uses Iterator. Many of filter functions are from this module.