Provided by: libiterator-util-perl_0.02+ds1-1_all 
NAME
Iterator::Util - Essential utilities for the Iterator class.
VERSION
This documentation describes version 0.02 of Iterator::Util, August 23, 2005.
SYNOPSIS
use Iterator::Util;
# Transform sequences
$iterator = imap { transformation code } $some_other_iterator;
# Filter sequences
$iterator = igrep { condition code } $some_other_iterator;
# Range of values (arithmetic sequence)
$iter = irange ($start, $end, $increment);
$iter = irange ($start, $end);
$iter = irange ($start);
# Iterate over an arbitrary list
$iter = ilist (item, item, ...);
$iter = ilist (@items);
# Iterate over an array, by reference
$iter = iarray (\@array);
# Return at most $num items from an iterator
$iter = ihead ($num, $some_other_iterator);
@values = ihead ($num, $some_other_iterator);
# Append multiple iterators into one
$iter = iappend ($it1, $it2, $it3, ...);
# Apply a function to pairs of iterator values
$iter = ipairwise {code} $iter_A, $iter_B;
# Skip the first $num values of an iterator
$iter = iskip ($num, $some_other_iterator);
# Skip values from an iterator until a condition is met
$iter = iskip_until {code} $some_other_iterator;
# Mesh iterators together
$iter = imesh ($iter, $iter, ...);
$iter = izip ($iter, $iter, ...);
# Return each value of an iterator once
$iter = iuniq ($another_iterator);
DESCRIPTION
This module implements many useful functions for creating and manipulating iterator
objects.
An "iterator" is an object, represented as a code block that generates the "next value" of
a sequence, and generally implemented as a closure. For further information, including a
tutorial on using iterator objects, see the Iterator documentation.
FUNCTIONS
imap
$iter = imap { transformation code } $some_other_iterator;
Returns an iterator that is a transformation of some other iterator. Within the
transformation code, $_ is set to each value of the other iterator, in turn.
Examples:
$evens = imap { $_ * 2 } irange (0); # returns 0, 2, 4, ...
$squares = imap { $_ * $_ } irange (7); # 49, 64, 81, 100, ...
igrep
$iter = igrep { condition } $some_other_iterator;
Returns an iterator that selectively returns values from some other iterator. Within
the "condition" code, $_ is set to each value of the other iterator, in turn.
Examples:
$fives = igrep { $_ % 5 == 0 } irange (0,10); # returns 0, 5, 10
$small = igrep { $_ < 10 } irange (8,12); # returns 8, 9
irange
$iter = irange ($start, $end, $increment);
$iter = irange ($start, $end);
$iter = irange ($start);
"irange" returns a sequence of numbers. The sequence begins with $start, ends at
$end, and steps by $increment. This is sort of the Iterator version of a "for" loop.
If $increment is not specified, 1 is used. $increment may be negative -- or even
zero, in which case iterator returns an infinite sequence of $start.
If $end is not specified (is "undef"), the sequence is infinite.
Examples:
$iter = irange (1, 2); # Iterate from 1 to 2
$val = $iter->value(); # $val is now 1.
$val = $iter->value(); # $val is now 2.
$bool = $iter->is_exhausted(); # $bool is now true.
$iter = irange (10, 8, -1); # Iterate from 10 down to 8
$iter = irange (1); # Iterate from 1, endlessly.
ilist
$iter = ilist (@items);
Returns an iterator that iterates over an arbitrary sequence of values. It's sort of
an Iterator version of "foreach".
This function makes an internal copy of the list, so it may not be appropriate for an
extremely large list.
Example:
$iter = ilist (4, 'minus five', @foo, 7);
$val = $iter->value(); # $val is now 4
$val = $iter->value(); # $val is now 'minus five'
...
iarray
$iter = iarray (\@array);
Returns an iterator that iterates over an array. Note that since it uses a reference
to that array, if you modify the array, that will be reflected in the values returned
by the iterator. This may be What You Want. Or it may cause Hard-To-Find Bugs.
ihead
$iter = ihead ($num, $some_other_iterator);
@values = ihead ($num, $some_iterator);
In scalar context, creates an iterator that returns at most $num items from another
iterator, then stops.
In list context, returns the first $num items from the iterator. If $num is "undef",
all remaining values are pulled from the iterator until it is exhausted. Use "undef"
with caution; iterators can be huge -- or infinite.
Examples:
$iota5 = ihead 5, irange 1; # returns 1, 2, 3, 4, 5.
$iter = irange 1; # infinite sequence, starting with 1
@vals = ihead (5, $iter); # @vals is (1, 2, 3, 4, 5)
$nextval = $iter->value; # $nextval is 6.
iappend
$iter = iappend (@list_of_iterators);
Creates an iterator that consists of any number of other iterators glued together.
The resulting iterator pulls values from the first iterator until it's exhausted, then
from the second, and so on.
ipairwise
$iter = ipairwise {code} $it_A, $it_B;
Creates a new iterator which applies "{code}" to pairs of elements of two other
iterators, $it_A and $it_B in turn. The pairs are assigned to $a and $b before
invoking the code.
The new iterator is exhausted when either $it_A or $it_B are exhausted.
This function is analogous to the pairwise function from List::MoreUtils.
Example:
$first = irange 1; # 1, 2, 3, 4, ...
$second = irange 4, undef, 2; # 4, 6, 8, 10, ...
$third = ipairwise {$a * $b} $first, $second; # 4, 12, 24, 40, ...
iskip
$iter = iskip ($num, $another_iterator);
Returns an iterator that contains the values of $another_iterator, minus the first
$num values. In other words, skips the first $num values of $another_iterator.
Example:
$iter = ilist (24, -1, 7, 8); # Bunch of random values
$cdr = iskip 1, $iter; # "pop" the first value
$val = $cdr->value(); # $val is -1.
iskip_until
$iter = iskip_until {code} $another_iterator;
Returns an iterator that skips the leading values of $another_iterator until "{code}"
evaluates to true for one of its values. "{code}" can refer to the current value as
$_.
Example:
$iter = iskip_until {$_ > 5} irange 1; # returns 6, 7, 8, 9, ...
imesh
izip
$iter = imesh ($iter1, $iter2, ...);
This iterator accepts any number of other iterators, and "meshes" their values
together. First it returns the first value of the first iterator, then the first
value of the second iterator, and so on, until it has returned the first value of all
of its iterator arguments. Then it goes back and returns the second value of the
first iterator, and so on. It stops when any of its iterator arguments is exhausted.
Example:
$i1 = ilist ('a', 'b', 'c');
$i2 = ilist (1, 2, 3);
$i3 = ilist ('rock', 'paper', 'scissors');
$iter = imesh ($i1, $i2, $i3);
# $iter will return, in turn, 'a', 1, 'rock', 'b', 2, 'paper', 'c',...
"izip" is a synonym for "imesh".
iuniq
$iter = iuniq ($another_iterator);
Creates an iterator to return unique values from another iterator; weeds out
duplicates.
Example:
$iter = ilist (1, 2, 2, 3, 1, 4);
$uniq = iuniq ($iter); # returns 1, 2, 3, 4.
EXPORTS
All function names are exported to the caller's namespace by default.
DIAGNOSTICS
Iterator::Util uses Exception::Class objects for throwing exceptions. If you're not
familiar with Exception::Class, don't worry; these exception objects work just like $@
does with "die" and "croak", but they are easier to work with if you are trapping errors.
See the Iterator module documentation for more information on trapping and handling these
exceptions.
• Parameter Errors
Class: "Iterator::X::Parameter_Error"
You called an Iterator method with one or more bad parameters. Since this is almost
certainly a coding error, there is probably not much use in handling this sort of
exception.
As a string, this exception provides a human-readable message about what the problem
was.
• Exhausted Iterators
Class: "Iterator::X::Exhausted"
You called "value|Iterator/value" on an iterator that is exhausted; that is, there are
no more values in the sequence to return.
As a string, this exception is "Iterator is exhausted."
• User Code Exceptions
Class: "Iterator::X::User_Code_Error"
This exception is thrown when the sequence generation code throws any sort of error
besides "Am_Now_Exhausted". This could be because your code explicitly threw an error
(that is, "die"d), or because it otherwise encountered an exception (any runtime
error).
This exception has one method, "eval_error", which returns the original $@ that was
trapped by the Iterator object. This may be a string or an object, depending on how
"die" was invoked.
As a string, this exception evaluates to the stringified $@.
• I/O Errors
Class: "Iterator::X::IO_Error"
This exception is thrown when any sort of I/O error occurs; this only happens with the
filesystem iterators.
This exception has one method, "os_error", which returns the original $! that was
trapped by the Iterator object.
As a string, this exception provides some human-readable information along with $!.
• Internal Errors
Class: "Iterator::X::Internal_Error"
Something happened that I thought couldn't possibly happen. I would appreciate it if
you could send me an email message detailing the circumstances of the error.
REQUIREMENTS
Requires the following additional modules:
Iterator
SEE ALSO
Higher Order Perl, Mark Jason Dominus, Morgan Kauffman 2005.
<http://perl.plover.com/hop/>
THANKS
Much thanks to Will Coleda and Paul Lalli (and the RPI lily crowd in general) for
suggestions for the pre-release version.
AUTHOR / COPYRIGHT
Eric J. Roode, roode@cpan.org
Copyright (c) 2005 by Eric J. Roode. All Rights Reserved. This module is free software;
you can redistribute it and/or modify it under the same terms as Perl itself.
To avoid my spam filter, please include "Perl", "module", or this module's name in the
message's subject line, and/or GPG-sign your message.