Current File : //usr/lib64/perl5/vendor_perl/List/Util.pm
# List::Util.pm
#
# Copyright (c) 1997-2009 Graham Barr <gbarr@pobox.com>. All rights reserved.
# This program is free software; you can redistribute it and/or
# modify it under the same terms as Perl itself.
#
# This module is normally only loaded if the XS module is not available
package List::Util;
use strict;
require Exporter;
our @ISA = qw(Exporter);
our @EXPORT_OK = qw(first min max minstr maxstr reduce sum sum0 shuffle);
our $VERSION = "1.27";
our $XS_VERSION = $VERSION;
$VERSION = eval $VERSION;
require XSLoader;
XSLoader::load('List::Util', $XS_VERSION);
sub sum0
{
return 0 unless @_;
goto ∑
}
1;
__END__
=head1 NAME
List::Util - A selection of general-utility list subroutines
=head1 SYNOPSIS
use List::Util qw(first max maxstr min minstr reduce shuffle sum);
=head1 DESCRIPTION
C<List::Util> contains a selection of subroutines that people have
expressed would be nice to have in the perl core, but the usage would
not really be high enough to warrant the use of a keyword, and the size
so small such that being individual extensions would be wasteful.
By default C<List::Util> does not export any subroutines. The
subroutines defined are
=over 4
=item first BLOCK LIST
Similar to C<grep> in that it evaluates BLOCK setting C<$_> to each element
of LIST in turn. C<first> returns the first element where the result from
BLOCK is a true value. If BLOCK never returns true or LIST was empty then
C<undef> is returned.
$foo = first { defined($_) } @list # first defined value in @list
$foo = first { $_ > $value } @list # first value in @list which
# is greater than $value
This function could be implemented using C<reduce> like this
$foo = reduce { defined($a) ? $a : wanted($b) ? $b : undef } undef, @list
for example wanted() could be defined() which would return the first
defined value in @list
=item max LIST
Returns the entry in the list with the highest numerical value. If the
list is empty then C<undef> is returned.
$foo = max 1..10 # 10
$foo = max 3,9,12 # 12
$foo = max @bar, @baz # whatever
This function could be implemented using C<reduce> like this
$foo = reduce { $a > $b ? $a : $b } 1..10
=item maxstr LIST
Similar to C<max>, but treats all the entries in the list as strings
and returns the highest string as defined by the C<gt> operator.
If the list is empty then C<undef> is returned.
$foo = maxstr 'A'..'Z' # 'Z'
$foo = maxstr "hello","world" # "world"
$foo = maxstr @bar, @baz # whatever
This function could be implemented using C<reduce> like this
$foo = reduce { $a gt $b ? $a : $b } 'A'..'Z'
=item min LIST
Similar to C<max> but returns the entry in the list with the lowest
numerical value. If the list is empty then C<undef> is returned.
$foo = min 1..10 # 1
$foo = min 3,9,12 # 3
$foo = min @bar, @baz # whatever
This function could be implemented using C<reduce> like this
$foo = reduce { $a < $b ? $a : $b } 1..10
=item minstr LIST
Similar to C<min>, but treats all the entries in the list as strings
and returns the lowest string as defined by the C<lt> operator.
If the list is empty then C<undef> is returned.
$foo = minstr 'A'..'Z' # 'A'
$foo = minstr "hello","world" # "hello"
$foo = minstr @bar, @baz # whatever
This function could be implemented using C<reduce> like this
$foo = reduce { $a lt $b ? $a : $b } 'A'..'Z'
=item reduce BLOCK LIST
Reduces LIST by calling BLOCK, in a scalar context, multiple times,
setting C<$a> and C<$b> each time. The first call will be with C<$a>
and C<$b> set to the first two elements of the list, subsequent
calls will be done by setting C<$a> to the result of the previous
call and C<$b> to the next element in the list.
Returns the result of the last call to BLOCK. If LIST is empty then
C<undef> is returned. If LIST only contains one element then that
element is returned and BLOCK is not executed.
$foo = reduce { $a < $b ? $a : $b } 1..10 # min
$foo = reduce { $a lt $b ? $a : $b } 'aa'..'zz' # minstr
$foo = reduce { $a + $b } 1 .. 10 # sum
$foo = reduce { $a . $b } @bar # concat
If your algorithm requires that C<reduce> produce an identity value, then
make sure that you always pass that identity value as the first argument to prevent
C<undef> being returned
$foo = reduce { $a + $b } 0, @values; # sum with 0 identity value
=item shuffle LIST
Returns the elements of LIST in a random order
@cards = shuffle 0..51 # 0..51 in a random order
=item sum LIST
Returns the sum of all the elements in LIST. If LIST is empty then
C<undef> is returned.
$foo = sum 1..10 # 55
$foo = sum 3,9,12 # 24
$foo = sum @bar, @baz # whatever
This function could be implemented using C<reduce> like this
$foo = reduce { $a + $b } 1..10
If your algorithm requires that C<sum> produce an identity of 0, then
make sure that you always pass C<0> as the first argument to prevent
C<undef> being returned
$foo = sum 0, @values;
=item sum0 LIST
Similar to C<sum>, except this returns 0 when given an empty list, rather
than C<undef>.
=back
=head1 KNOWN BUGS
With perl versions prior to 5.005 there are some cases where reduce
will return an incorrect result. This will show up as test 7 of
reduce.t failing.
=head1 SUGGESTED ADDITIONS
The following are additions that have been requested, but I have been reluctant
to add due to them being very simple to implement in perl
# One argument is true
sub any { $_ && return 1 for @_; 0 }
# All arguments are true
sub all { $_ || return 0 for @_; 1 }
# All arguments are false
sub none { $_ && return 0 for @_; 1 }
# One argument is false
sub notall { $_ || return 1 for @_; 0 }
# How many elements are true
sub true { scalar grep { $_ } @_ }
# How many elements are false
sub false { scalar grep { !$_ } @_ }
=head1 SEE ALSO
L<Scalar::Util>, L<List::MoreUtils>
=head1 COPYRIGHT
Copyright (c) 1997-2007 Graham Barr <gbarr@pobox.com>. All rights reserved.
This program is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.
=cut
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