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1 | # List::Util.pm |
2 | # |
3 | # Copyright (c) 1997-2009 Graham Barr <gbarr@pobox.com>. All rights reserved. |
4 | # This program is free software; you can redistribute it and/or |
5 | # modify it under the same terms as Perl itself. |
6 | # |
7 | # This module is normally only loaded if the XS module is not available |
8 | |
9 | package List::Util; |
10 | |
11 | use strict; |
12 | use vars qw(@ISA @EXPORT_OK $VERSION $XS_VERSION $TESTING_PERL_ONLY); |
13 | require Exporter; |
14 | |
15 | @ISA = qw(Exporter); |
16 | @EXPORT_OK = qw(first min max minstr maxstr reduce sum shuffle); |
17 | $VERSION = "1.22"; |
18 | $XS_VERSION = $VERSION; |
19 | $VERSION = eval $VERSION; |
20 | |
21 | eval { |
22 | # PERL_DL_NONLAZY must be false, or any errors in loading will just |
23 | # cause the perl code to be tested |
24 | local $ENV{PERL_DL_NONLAZY} = 0 if $ENV{PERL_DL_NONLAZY}; |
25 | eval { |
26 | require XSLoader; |
27 | XSLoader::load('List::Util', $XS_VERSION); |
28 | 1; |
29 | } or do { |
30 | require DynaLoader; |
31 | local @ISA = qw(DynaLoader); |
32 | bootstrap List::Util $XS_VERSION; |
33 | }; |
34 | } unless $TESTING_PERL_ONLY; |
35 | |
36 | |
37 | if (!defined &sum) { |
38 | require List::Util::PP; |
39 | List::Util::PP->import; |
40 | } |
41 | |
42 | 1; |
43 | |
44 | __END__ |
45 | |
46 | =head1 NAME |
47 | |
48 | List::Util - A selection of general-utility list subroutines |
49 | |
50 | =head1 SYNOPSIS |
51 | |
52 | use List::Util qw(first max maxstr min minstr reduce shuffle sum); |
53 | |
54 | =head1 DESCRIPTION |
55 | |
56 | C<List::Util> contains a selection of subroutines that people have |
57 | expressed would be nice to have in the perl core, but the usage would |
58 | not really be high enough to warrant the use of a keyword, and the size |
59 | so small such that being individual extensions would be wasteful. |
60 | |
61 | By default C<List::Util> does not export any subroutines. The |
62 | subroutines defined are |
63 | |
64 | =over 4 |
65 | |
66 | =item first BLOCK LIST |
67 | |
68 | Similar to C<grep> in that it evaluates BLOCK setting C<$_> to each element |
69 | of LIST in turn. C<first> returns the first element where the result from |
70 | BLOCK is a true value. If BLOCK never returns true or LIST was empty then |
71 | C<undef> is returned. |
72 | |
73 | $foo = first { defined($_) } @list # first defined value in @list |
74 | $foo = first { $_ > $value } @list # first value in @list which |
75 | # is greater than $value |
76 | |
77 | This function could be implemented using C<reduce> like this |
78 | |
79 | $foo = reduce { defined($a) ? $a : wanted($b) ? $b : undef } undef, @list |
80 | |
81 | for example wanted() could be defined() which would return the first |
82 | defined value in @list |
83 | |
84 | =item max LIST |
85 | |
86 | Returns the entry in the list with the highest numerical value. If the |
87 | list is empty then C<undef> is returned. |
88 | |
89 | $foo = max 1..10 # 10 |
90 | $foo = max 3,9,12 # 12 |
91 | $foo = max @bar, @baz # whatever |
92 | |
93 | This function could be implemented using C<reduce> like this |
94 | |
95 | $foo = reduce { $a > $b ? $a : $b } 1..10 |
96 | |
97 | =item maxstr LIST |
98 | |
99 | Similar to C<max>, but treats all the entries in the list as strings |
100 | and returns the highest string as defined by the C<gt> operator. |
101 | If the list is empty then C<undef> is returned. |
102 | |
103 | $foo = maxstr 'A'..'Z' # 'Z' |
104 | $foo = maxstr "hello","world" # "world" |
105 | $foo = maxstr @bar, @baz # whatever |
106 | |
107 | This function could be implemented using C<reduce> like this |
108 | |
109 | $foo = reduce { $a gt $b ? $a : $b } 'A'..'Z' |
110 | |
111 | =item min LIST |
112 | |
113 | Similar to C<max> but returns the entry in the list with the lowest |
114 | numerical value. If the list is empty then C<undef> is returned. |
115 | |
116 | $foo = min 1..10 # 1 |
117 | $foo = min 3,9,12 # 3 |
118 | $foo = min @bar, @baz # whatever |
119 | |
120 | This function could be implemented using C<reduce> like this |
121 | |
122 | $foo = reduce { $a < $b ? $a : $b } 1..10 |
123 | |
124 | =item minstr LIST |
125 | |
126 | Similar to C<min>, but treats all the entries in the list as strings |
127 | and returns the lowest string as defined by the C<lt> operator. |
128 | If the list is empty then C<undef> is returned. |
129 | |
130 | $foo = minstr 'A'..'Z' # 'A' |
131 | $foo = minstr "hello","world" # "hello" |
132 | $foo = minstr @bar, @baz # whatever |
133 | |
134 | This function could be implemented using C<reduce> like this |
135 | |
136 | $foo = reduce { $a lt $b ? $a : $b } 'A'..'Z' |
137 | |
138 | =item reduce BLOCK LIST |
139 | |
140 | Reduces LIST by calling BLOCK, in a scalar context, multiple times, |
141 | setting C<$a> and C<$b> each time. The first call will be with C<$a> |
142 | and C<$b> set to the first two elements of the list, subsequent |
143 | calls will be done by setting C<$a> to the result of the previous |
144 | call and C<$b> to the next element in the list. |
145 | |
146 | Returns the result of the last call to BLOCK. If LIST is empty then |
147 | C<undef> is returned. If LIST only contains one element then that |
148 | element is returned and BLOCK is not executed. |
149 | |
150 | $foo = reduce { $a < $b ? $a : $b } 1..10 # min |
151 | $foo = reduce { $a lt $b ? $a : $b } 'aa'..'zz' # minstr |
152 | $foo = reduce { $a + $b } 1 .. 10 # sum |
153 | $foo = reduce { $a . $b } @bar # concat |
154 | |
155 | If your algorithm requires that C<reduce> produce an identity value, then |
156 | make sure that you always pass that identity value as the first argument to prevent |
157 | C<undef> being returned |
158 | |
159 | $foo = reduce { $a + $b } 0, @values; # sum with 0 identity value |
160 | |
161 | =item shuffle LIST |
162 | |
163 | Returns the elements of LIST in a random order |
164 | |
165 | @cards = shuffle 0..51 # 0..51 in a random order |
166 | |
167 | =item sum LIST |
168 | |
169 | Returns the sum of all the elements in LIST. If LIST is empty then |
170 | C<undef> is returned. |
171 | |
172 | $foo = sum 1..10 # 55 |
173 | $foo = sum 3,9,12 # 24 |
174 | $foo = sum @bar, @baz # whatever |
175 | |
176 | This function could be implemented using C<reduce> like this |
177 | |
178 | $foo = reduce { $a + $b } 1..10 |
179 | |
180 | If your algorithm requires that C<sum> produce an identity of 0, then |
181 | make sure that you always pass C<0> as the first argument to prevent |
182 | C<undef> being returned |
183 | |
184 | $foo = sum 0, @values; |
185 | |
186 | =back |
187 | |
188 | =head1 KNOWN BUGS |
189 | |
190 | With perl versions prior to 5.005 there are some cases where reduce |
191 | will return an incorrect result. This will show up as test 7 of |
192 | reduce.t failing. |
193 | |
194 | =head1 SUGGESTED ADDITIONS |
195 | |
196 | The following are additions that have been requested, but I have been reluctant |
197 | to add due to them being very simple to implement in perl |
198 | |
199 | # One argument is true |
200 | |
201 | sub any { $_ && return 1 for @_; 0 } |
202 | |
203 | # All arguments are true |
204 | |
205 | sub all { $_ || return 0 for @_; 1 } |
206 | |
207 | # All arguments are false |
208 | |
209 | sub none { $_ && return 0 for @_; 1 } |
210 | |
211 | # One argument is false |
212 | |
213 | sub notall { $_ || return 1 for @_; 0 } |
214 | |
215 | # How many elements are true |
216 | |
217 | sub true { scalar grep { $_ } @_ } |
218 | |
219 | # How many elements are false |
220 | |
221 | sub false { scalar grep { !$_ } @_ } |
222 | |
223 | =head1 SEE ALSO |
224 | |
225 | L<Scalar::Util>, L<List::MoreUtils> |
226 | |
227 | =head1 COPYRIGHT |
228 | |
229 | Copyright (c) 1997-2007 Graham Barr <gbarr@pobox.com>. All rights reserved. |
230 | This program is free software; you can redistribute it and/or |
231 | modify it under the same terms as Perl itself. |
232 | |
233 | =cut |