oracular (3) List::Maker.3pm.gz
NAME
List::Maker - Generate more sophisticated lists than just $a..$b
VERSION
This document describes List::Maker version 0.005
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.
Under Perl 5.10 and later the module is also lexically scoped in its effects. That is, under Perls that
support it, the change in the behaviour of angle brackets is confined to the specific lexical scope into
which the module was imported.
Under Perl 5.8 and earlier, loading the module changes the effect of "<...>" and "glob()" for the
remainder of the current package in the current file.
This means:
# Code Under 5.8 or earlier Under 5.10 or later
==================== ==================== ===================
@list = <1..10>; normal glob() normal glob()
{
use List::Maker; installs in file installs in block
@list = <1..10>; generates list generates list
}
@list = <1..10>; generates list normal glob()
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} >
Randomly selecting from lists
In addition to (or instead of) specifying a filter on a list, you can also select a specific number of
the list's items at random, by appending ":pick" N to the list specification.
For example:
$N_random_percentages = <0..100 : pick $N >;
@any_three_primes = <3,5..99> : is_prime(I) : pick 3>;
$one_available = < ^$max : !allocated{T} :pick>
The requested number of elements are picked at random, and without replacement. If the number of elements
to be picked is omitted, a single element is randomly picked.
You can also pick with replacement (which is equivalent to rolling some number of M-sided dice, with one
list element on each face), by using ":roll" instead of ":pick":
$N_nonunique_random_percentages = <0..100 : roll $N >;
@three_nonunique_primes = <3,5..99> : is_prime(I) : roll 3>;
$one_available = < ^$max : !allocated{T} :roll>
If the number of elements to be rolled is omitted, a single element is randomly rolled (which is exactly
the same as randomly picking it).
Note that, because each requested "roll" is independent, it's entirely possible for one or more values to
be selected repeatedly.
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 => $sub_ref...);
Each pattern is added to the list of syntax checkers and, if it matches, the corresponding subroutine is
called to furnish the result of the "<...>". User-defined handlers are tested in the same order that they
are defined, but before the standard built-in formats described above.
ALTERNATE INTERFACE
If an argument is passed to the "use List::Maker" statement, then that argument is used as the name of a
subroutine to be installed in the current package. That subroutine then expects a single argument, which
may be used to generate any of the lists described above.
In other words, passing an argument to "use List::Maker" creates an explicit list-making subroutine,
rather than hijacking the built-in "<..>" and "glob()".
For example:
use List::Maker 'range';
for (range '1..100 x 5') {
print "$_: $result{$_}\n";
}
use List::Maker 'roll';
if (roll '3d12' > 20) {
print "The $creature hits you\n";
}
use List::Maker 'conjoin';
print scalar 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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