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Author image Damian Conway

NAME

List::Maker - Generate more sophisticated lists than just $a..$b

VERSION

This document describes List::Maker version 0.0.3

SYNOPSIS

    use List::Maker;

    @list = <1..10>;                      # (1,2,3,4,5,6,7,8,9,10)

    @list = <10..1>;                      # (10,9,8,7,6,5,4,3,2,1)

    @list = <1,3,..10>                    # (1,3,5,7,9)
    @list = <1..10 x 2>                   # (1,3,5,7,9)
  
    @list = <0..10 : prime N>;            # (2,3,5,7)
    @list = <1,3,..30  : /7/>             # (7,17,27)

    @words = < a list of words >;         # ('a', 'list', 'of', 'words')
    @words = < 'a list' "of words" >;     # ('a list', 'of words')

  

DESCRIPTION

The List::Maker module hijacks Perl's built-in file globbing syntax (< *.pl > and glob '*.pl') and retargets it at list creation.

The rationale is simple: most people rarely if ever glob a set of files, but they have to create lists in almost every program they write. So the list construction syntax should be easier than the filename expansion syntax.

INTERFACE

Once the module has been loaded, angle brackets no longer expand a shell pattern into a list of files. Instead, they expand a list specification into a list of values.

Numeric lists

Numeric list specifications may take any of the following 4 forms:

    Type           Syntax                  For example     Produces
    ==========     ===================     ===========     ===========
    Count up       <MIN..MAX>              <1..5>          (1,2,3,4,5)
    Count down     <MAX..MIN>              <5..1>          (5,4,3,2,1)
    Count by       <START..END x STEP>     <1..10 x 3>     (1,4,7,10)
    Count via      <START, NEXT,..END>     <1, 3,..10>     (1,3,5,7,9)

The numbers don't have to be integers either:

    @scores = <0.5..4.5>;      # same as: (0.5, 1.5, 2.5, 3.5, 4.5)

    @steps = <1..0 x -0.2>;    # same as: (1, 0.8, 0.6, 0.4, 0.2, 0)
    

Filtered numeric lists

Any of the four styles of numeric list may also have a filter applied to it, by appending a colon, followed by a boolean expression:

    @odds   = <1..100 : \$_ % 2 != 0 >;

    @primes = <3,5..99> : is_prime(\$_) >;

    @available = <1..$max : !allocated{\$_} >

    @ends_in_7 = <1..1000 : /7$/ >

The boolean expression is tested against each element of the list, and only those for which it is true are retained. During these tests each element is aliased to $_. However, since angle brackets interpolate, it's necessary to escape any explicit reference to $_ within the filtering expression, as in the first three examples above.

That often proves to be annoying, so the module also allows the candidate value to be referred to using any single uppercase letter (which is replaced with \$_ when the filter is applied. So the previous examples could also be written:

    @odds   = <1..100 : N % 2 != 0 >;

    @primes = <3,5..99> : is_prime(N) >;

    @available = <1..$max : !allocated{N} >

or (since the specific letter is irrelevant):

    @odds   = <1..100 : X % 2 != 0 >;

    @primes = <3,5..99> : is_prime(I) >;

    @available = <1..$max : !allocated{T} >

String lists

Any list specification that doesn't conform to one of the four pattern described above is taken to be a list of whitespace-separated strings, like a qw{...} list:

    @words = <Eat at Joe's>;     # same as: ( 'Eat', 'at', 'Joe\'s' )

However, unlike a qw{...}, these string lists interpolate (before listification):

    $whose = q{Joe's};

    @words = <Eat at $whose>;    # same as: ( 'Eat', 'at', 'Joe\'s' )

More interestingly, the words in these lists can be quoted to change the default whitespace separation. For example:

    @names = <Tom Dick "Harry Potter">;   
                        # same as: ( 'Tom', 'Dick', 'Harry Potter' )
    

Single quotes may be also used, but this may be misleading, since the overall list still interpolates in that case:

    @names = <Tom Dick '$Harry{Potter}'>;   
                        # same as: ( 'Tom', 'Dick', "$Harry{Potter}" )

DIAGNOSTICS

Sequence <%s, %s, %s...> will never reach %s

The specified numeric list didn't make sense. Typically, because you specified an increasing list with a negative step size (or vice versa).

CONFIGURATION AND ENVIRONMENT

List::Maker requires no configuration files or environment variables.

DEPENDENCIES

None.

INCOMPATIBILITIES

Using this module prevents you from using <...> or glob() to expand file lists. You would need to use the File::Glob module directly:

    use File::Glob;

    my @files = bsd_glob("*.pl");

BUGS AND LIMITATIONS

No bugs have been reported.

Please report any bugs or feature requests to bug-list-maker@rt.cpan.org, or through the web interface at http://rt.cpan.org.

AUTHOR

Damian Conway <DCONWAY@CPAN.org>

LICENCE AND COPYRIGHT

Copyright (c) 2005, Damian Conway <DCONWAY@CPAN.org>. All rights reserved.

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See perlartistic.

DISCLAIMER OF WARRANTY

BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE SOFTWARE, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE SOFTWARE "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH YOU. SHOULD THE SOFTWARE PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR, OR CORRECTION.

IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE SOFTWARE AS PERMITTED BY THE ABOVE LICENCE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE SOFTWARE (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE SOFTWARE TO OPERATE WITH ANY OTHER SOFTWARE), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.