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use strict;
use warnings;
use 5.008001;

# Module code.
{
    package Scalar::Bool;
    use parent qw(Exporter);
    use Scalar::Util ();

    BEGIN { our @EXPORT_OK = qw(true false is_bool) }

    use overload (
        q{bool} => \&_invert,
        fallback => 1,
    );

    my $true = bless(
        \(
            do { my $v = 1 }
        ), "Scalar::Bool::True"
    );
    sub true () { $true }

    my $false = bless(
        \(
            do { my $v = 0 }
        ), "Scalar::Bool::False"
    );
    sub false () { $false }

    sub is_bool {
        my $value = shift;
        return 0 unless Scalar::Util::reftype($value) eq 'SCALAR';
        return 0 unless overload::Method($value, 'bool');
        return 1;
    }

    package Scalar::Bool::True;
    our @ISA = qw(Scalar::Bool);
    package Scalar::Bool::False;
    our @ISA = qw(Scalar::Bool);
}

# Test code.
{
    BEGIN { Scalar::Bool->import(qw(true false is_bool)); }
    use Test::More;

    note "True:";
    note true;
    note "False:";
    note false;

    if (true) {
        pass;
    } else {
        fail;
    }
    unless (false) {
        pass;
    } else {
        fail;
    }
    ok(is_bool(true));
    ok(is_bool(false));

    done_testing;
}