List::Maker(3pm) User Contributed Perl Documentation List::Maker(3pm)
NAME
List::Maker - Generate more sophisticated lists than just $a..$b
VERSION
This document describes List::Maker version 0.0.5
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)
@list = < ^10 >; # (0,1,2,3,4,5,6,7,8,9)
@list = < ^@array >; # (0..$#array)
@words = < a list of words >; # ('a', 'list', 'of', 'words')
@words = < 'a list' "of words" >; # ('a list', 'of words')
use List::Maker 'listify';
@list = listify '1..10'; # (1,2,3,4,5,6,7,8,9,10)
use List::Maker 'make_list';
@list = make_list '10..1'; # (10,9,8,7,6,5,4,3,2,1)
use List::Maker 'ql';
@list = ql'1..10 x 2'; # (1,3,5,7,9)
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.
Alternatively, you can load the module with an explicit name, and it creates a subroutine of that name that builds the same kinds of lists
for you (leaving the globbing mechanism unaltered).
INTERFACE
Within any file in which the module has been explicitly loaded:
use List::Maker;
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 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 to < ^LIMIT > < ^5 > (0,1,2,3,4)
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 various 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 = < ^$max : !allocated{$_} >
@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 = < ^$max : !allocated{N} >
or (since the specific letter is irrelevant):
@odds = <1..100 : X % 2 != 0 >;
@primes = <3,5..99> : is_prime(I) >;
@available = < ^$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}" )
In a scalar context, any string list is converted to the standard English representation:
$names = <Tom>; # 'Tom'
$names = <Tom Dick>; # 'Tom and Dick'
$names = <Tom Dick 'Harry Potter'>; # 'Tom, Dick, and Harry Potter'
Perl 6 repetition list operator
List::Maker also understands the Perl 6 "xx" listification operator:
@affirmations = <'aye' xx 5>; # ('aye','aye','aye','aye','aye')
Random number generation
The module understands two syntaxes for generating random numbers. It can generate a random number within a range:
$random = < 2r5.5 >; # 2 <= Random number < 5.5
It can also generate an "NdS" dice roll (i.e. the sum of rolling N dice, each with S sides):
$roll = < 3d12 >; # Sum of three 12-sided dice
The dice notation cares nothing for the laws of physics or rationality and so it will even allow you to specify a non-integer number of
"fractal dice", each with an non-integer numbers of sides:
$roll = < 3.7d12.3 >; # Sum of three-point-seven 12.3-sided dice
In a list context, the dice notation returns the results of each of the individual die rolls (including the partial result of a "fractal"
roll)
@rolls = < 3d12 >; # (6, 5, 12)
@rolls = < 3.7d12.3 >; # (6.1256, 5.9876, 12.0012, 0.3768)
The values returned in list context will always add up to the value that would have been returned in a scalar context.
User-defined syntax via "add_handler"
You can add new syntax variations to the "<...>" format using the "add_handler()" function:
add_handler($pattern => $sub_ref, $pattern => $sub_ref...);
Each pattern is added to the list of syntax checkers and, if it matches, the corresponding subroutine is called to furnish the result of
the "<...>". User-defined handlers are tested in the same order that they are defined, but before the standard built-in formats described
above.
ALTERNATE INTERFACE
If an argument is passed to the "use List::Maker" statement, then that argument is used as the name of a subroutine to be installed in the
current package. That subroutine then expects a single argument, which may be used to generate any of the lists described above.
In other words, passing an argument to "use List::Maker" creates an explicit list-making subroutine, rather than hijacking the built-in
"<..>" and "glob()".
For example:
use List::Maker 'range';
for (range '1..100 x 5') {
print "$_: $result{$_}
";
}
use List::Maker 'roll';
if (roll '3d12' > 20) {
print "The $creature hits you
";
}
use List::Maker 'conjoin';
print conjoin @names;
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 normally prevents you from using the built-in behaviours of "<...>" or "glob()" in any files that directly "use" the
module (though files that don't load the module are unaffected). In files that use the module, you would need to use the "File::Glob"
module directly:
use File::Glob;
my @files = bsd_glob("*.pl");
Alternatively, export the list maker by name (see "ALTERNATE INTERFACE").
BUGS AND LIMITATIONS
The lists generated are not lazy. So this:
for (<1..10000000>) {
...
}
will be vastly slower than:
for (1..10000000) {
...
}
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.
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perl v5.10.1 2010-11-05 List::Maker(3pm)