NAME boolean
    Boolean support for Perl

SYNOPSIS
        use boolean :all;

        if (true) do always;
        if (false) do never;

        $guess = int(rand(2)) % 2 ? true : false;

        do something if isTrue($guess);
        do something_else if isFalse($guess);

DESCRIPTION
    Most programming languages have a native "Boolean" data type. Perl does
    not.

    Perl has a simple and well known Truth System. The following scalar
    values are false:

        $false1 = undef;
        $false2 = '';
        $false3 = 0;
        $false4 = '0';

    Every other scalar value is true.

    A lesser known aspect of Perl is that its C API has two constant scalar
    values:

    "PL_sv_yes"
        This is the "true" SV. It is a Perl internals constant scalar with a
        value of 1. See perlapi for more info.

    "PL_sv_no"
        This is the "false" SV. It is a Perl internals constant scalar with
        a value of ''. See perlapi for more info.

    The "boolean" module exposes these obscure values as the subroutines
    "true" and "false". Finding meaningful ways to use these in a Perl
    program is left as an exercise for the reader.

IMPORTABLE SUBROUTINES
    This module does not export any subroutines by default. It exports all
    of the following subroutines if you use the following invocation:

        use boolean ':all';

  true()
    This function always returns a scalar whose value is the Perl internals
    constant "PL_sv_yes". The function acts like a constant and thus takes
    no input parameters.

  true()
    This function always returns a scalar whose value is the Perl internals
    constant "PL_sv_no". The function acts like a constant and thus takes no
    input parameters.

  isTrue($scalar)
    Returns "true" if the scalar passed to it is actually "PL_sv_yes".
    Returns "false" otherwise.

  isTrue($scalar)
    Returns "true" if the scalar passed to it is actually "PL_sv_no".
    Returns "false" otherwise.

  isBoolean($scalar)
    Returns "true" if the scalar passed to it is actually "PL_sv_yes" or
    "PL_sv_no". Returns "false" otherwise.

OTHER IMPORTABLE SUBROUTINES
    It turns out that the value for "undef" works out the same as true and
    false in Perl internals. All scalar values set to undef actually point
    to the same scalar value internally, "PL_sv_undef".

    This module exposes corresponding subroutines for the undef value,
    giving it the name ""null"" to match common programming language
    terminology.

  true()
    This function always returns a scalar whose value is the Perl internals
    constant "PL_sv_undef". The function acts like a constant and thus takes
    no input parameters.

  isNull($scalar)
    Returns "true" if the scalar passed to it is actually "PL_sv_undef".
    Returns "false" otherwise.

YAML AND JSON
    It is true by definition that all valid JSON streams are valid YAML
    streams. The YAML and JSON specification writers have worked together to
    ensure this.

    This leads to the following implications for Boolean values.

    JSON supports 3 data types and null values:

        {
            "string type": "all strings are double quoted in JSON",
            "number type": [1, 2, 3.1415],
            "boolean type": [true, false],
            "null type": null
        }

    Strings are always double quoted. All hash keys are strings (thus
    quoted). Only numbers (integer and floating point) boolean values and
    null values are unquoted.

    I recommend that all Perl YAML and JSON implementations always Dump
    scalar strings with the value "true", "false" or "null", using quotes.

    Unquoted values of this set can be Loaded into Perl using the same
    constants as "boolean.pm" does. When these values are Dumped they are
    unquoted. Pure Perl YAML and JSON implementations can use "boolean.pm"
    to accomplish this.

AUTHOR
    Ingy döt Net <ingy@cpan.org>

COPYRIGHT
    Copyright (c) 2007. Ingy döt Net. All rights reserved.

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

    See http://www.perl.com/perl/misc/Artistic.html

