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Util.pm
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2006-11-29
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258 lines
# List::Util.pm
#
# Copyright (c) 1997-2004 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.
package List::Util;
require Exporter;
@ISA = qw(Exporter);
@EXPORT_OK = qw(first min max minstr maxstr reduce sum shuffle);
$VERSION = "1.14";
$XS_VERSION = $VERSION;
$VERSION = eval $VERSION;
eval {
# PERL_DL_NONLAZY must be false, or any errors in loading will just
# cause the perl code to be tested
local $ENV{PERL_DL_NONLAZY} = 0 if $ENV{PERL_DL_NONLAZY};
require DynaLoader;
local @ISA = qw(DynaLoader);
bootstrap List::Util $XS_VERSION;
1
};
eval <<'ESQ' unless defined &reduce;
# This code is only compiled if the XS did not load
use vars qw($a $b);
sub reduce (&@) {
my $code = shift;
return shift unless @_ > 1;
my $caller = caller;
local(*{$caller."::a"}) = \my $a;
local(*{$caller."::b"}) = \my $b;
$a = shift;
foreach (@_) {
$b = $_;
$a = &{$code}();
}
$a;
}
sub sum (@) { reduce { $a + $b } @_ }
sub min (@) { reduce { $a < $b ? $a : $b } @_ }
sub max (@) { reduce { $a > $b ? $a : $b } @_ }
sub minstr (@) { reduce { $a lt $b ? $a : $b } @_ }
sub maxstr (@) { reduce { $a gt $b ? $a : $b } @_ }
sub first (&@) {
my $code = shift;
foreach (@_) {
return $_ if &{$code}();
}
undef;
}
sub shuffle (@) {
my @a=\(@_);
my $n;
my $i=@_;
map {
$n = rand($i--);
(${$a[$n]}, $a[$n] = $a[$i])[0];
} @_;
}
ESQ
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 : $b } 'A'..'Z'
=item reduce BLOCK LIST
Reduces LIST by calling BLOCK multiple times, setting C<$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
=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.
$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
=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 COPYRIGHT
Copyright (c) 1997-2004 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