NAME

HOP::Stream - "Higher Order Perl" streams

VERSION

Version 0.03

SYNOPSIS

DESCRIPTION

This package is based on the Stream.pm code from the book "Higher Order Perl", by Mark Jason Dominus.

A stream is conceptually similar to a linked list. However, we may have an infinite stream. As infinite amounts of data are frequently taxing to the memory of most systems, the tail of the list may be a promise. A promise, in this context, is merely a promise that the code will compute the rest of the list if necessary. Thus, the rest of the list does not exist until actually needed.

The documentation here is not complete. See "Higher Order Perl" by Mark Dominus for a full explanation. Further, this is ALPHA code. Patches and suggestions welcome.

EXPORT

The following functions may be exported upon demand. ":all" may be specified if you wish everything exported.

cutsort
drop
filter
head
insert
iterator_to_stream
list_to_stream
append
merge
node
promise
show
tail
transform
upto
upfrom

FUNCTIONS

node

 my $node = node( $head, $tail );

Returns a node for a stream.

The tail of the node may be a promise to compute the actual tail when needed.

head

  my $head = head( $node );

This function returns the head of a stream.

tail

 my $tail = tail( $stream );

Returns the tail of a stream.

is_node

  if ( is_node($tail) ) {
     ...
  }

Returns true if the tail of a node is a node. Generally this function is used internally.

is_promise

  if ( is_promise($tail) ) {
     ...
  }

Returns true if the tail of a node is a promise. Generally this function is used internally.

promise

  my $promise = promise { ... };

A utility function with a code prototype ("sub promise(&);") allowing one to specify a coderef with curly braces and omit the "sub" keyword.

show

 show( $stream, [ $number_of_nodes ] );

This is a debugging function that will return a text representation of $number_of_nodes of the stream $stream.

Omitting the second argument will print all elements of the stream. This is not recommended for infinite streams (duh).

The elements of the stream will be separated by the current value of $".

drop

  my $head = drop( $stream );

This is the "shift" function for streams. It returns the head of the stream and and modifies the stream in-place to be the tail of the stream.

transform

  my $new_stream = transform { $_[0] * 2 } $old_stream;

This is the "map" function for streams. It returns a new stream.

filter

  my $new_stream = filter { $_[0] % 2 } $old_stream;

This is the "grep" function for streams. It returns a new stream.

merge

  my $merged_stream = merge( $stream1, $stream2 );

This function takes two streams assumed to be in sorted order and merges them into a new stream, also in sorted order.

append

  my $merged_stream = append( $stream1, $stream2 );

This function takes a list of streams and attaches them together head-to-tail into a new stream.

list_to_stream

  my $stream = list_to_stream(@list);

Converts a list into a stream. The final item of "list" should be a promise or another stream. Thus, to generate the numbers one through ten, one could do this:

 my $stream = list_to_stream( 1 .. 9, node(10, undef) );
 # or
 my $stream = list_to_stream( 1 .. 9, node(10) );

iterator_to_stream

  my $stream = iterator_to_stream($iterator);

Converts an iterator into a stream. An iterator is merely a code reference which, when called, keeps returning elements until there are no more elements, at which point it returns "undef".

upto

  my $stream = upto($from_num, $to_num);

Given two numbers, $from_num and $to_num, returns an iterator which will return all of the numbers between $from_num and $to_num, inclusive.

upfrom

  my $stream = upfrom($num);

Similar to "upto", this function returns a stream which will generate an infinite list of numbers starting from $num.

AUTHOR

Mark Dominus, maintained by Curtis "Ovid" Poe, "<ovid@cpan.org>"

BUGS

Please report any bugs or feature requests to "bug-hop-stream@rt.cpan.org", or through the web interface at <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=HOP-Stream>. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.

ACKNOWLEDGEMENTS

Many thanks to Mark Dominus and Elsevier, Inc. for allowing this work to be republished.

COPYRIGHT & LICENSE

ABOUT THE SOFTWARE

All Software (code listings) presented in the book can be found on the companion website for the book (http://perl.plover.com/hop/) and is subject to the License agreements below.

LATEST VERSION

You can download the latest versions of these modules at <http://github.com/Ovid/hop/>. Feel free to fork and make changes.

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