sub are_hashes_equal($$) {

        my ($a, $b) = @_;  # hashrefs

        # number of keys in hashes must be the same

        return 0 unless keys %$a == keys %$b;

        # and each key-value pair in %$a must have an
        # identical key-value pair in %$b

        while (my ($key_a, $val_a) = each %$a) {
            return 0 unless exists $b->{$key_a}
                            && $b->{$key_a} eq $val_a;
        }

        return 1;
    }

##</code><code>##

    ($a,$b) = ($b,$a) if keys %$b > keys %$a

##</code><code>##

    use Test::LectroTest;

    Property {
        ##[ h <- Hash( Int, Int ) ]##
        are_hashes_equal( $h, $h ) == 1;
    }, name => "equal hashes are recognized as equal";

    Property {
        ##[ h <- Hash( Int, Int, length=>[1,] ) ]##
        my %h_diff = %$h;
        delete $h_diff{scalar each %$h};  # delete 1st key
        are_hashes_equal( $h, \%h_diff ) == 0;
    }, name => "differences in quantity of keys are detected";

    Property {
        ##[ h <- Hash( Int, Int, length=>[1,] ) ]##
        my %h_diff = %$h;
        delete $h_diff{scalar each %$h};  # delete 1st key
        $h_diff{a} = 1;                   # replace with "a" key
        are_hashes_equal( $h, \%h_diff ) == 0;
    }, name => "differences in values of keys are detected";

    Property {
        ##[ h <- Hash( Int, Int, length=>[1,] ) ]##
        my %h_diff = %$h;
        $h_diff{scalar each %$h}++;  # increment 1st value
        are_hashes_equal( $h, \%h_diff ) == 0;
    }, name => "differences in values are detected";

##</code><code>##

1..4
ok 1 - 'equal hashes are recognized as equal' (1000 attempts)
ok 2 - 'differences in quantity of keys are detected' (1000 attempts)
ok 3 - 'differences in values of keys are detected' (1000 attempts)
ok 4 - 'differences in values are detected' (1000 attempts)

##</code><code>##

#!/usr/bin/perl

# Tom Moertel <tom@moertel.com> 2004-10-12

use warnings;
use strict;

sub are_hashes_equal($$) {

    my ($a, $b) = @_;

    # number of keys in hashes must be the same

    return 0 unless keys %$a == keys %$b;

    # and each key-value pair in %$a must have an
    # identical key-value pair in %$b

    while (my ($key_a, $val_a) = each %$a) {
        return 0 unless exists $b->{$key_a}
                        && $b->{$key_a} eq $val_a;
    }

    return 1;
}


# we use LectroTest to test whether the following
# properties hold for our implementation above

use Test::LectroTest;

Property {
    ##[ h <- Hash( Int, Int ) ]##
    are_hashes_equal( $h, $h ) == 1;
}, name => "equal hashes are recognized as equal";

Property {
    ##[ h <- Hash( Int, Int, length=>[1,] ) ]##
    my %h_diff = %$h;
    delete $h_diff{scalar each %$h};  # delete 1st key
    are_hashes_equal( $h, \%h_diff ) == 0;
}, name => "differences in quantity of keys are detected";

Property {
    ##[ h <- Hash( Int, Int, length=>[1,] ) ]##
    my %h_diff = %$h;
    delete $h_diff{scalar each %$h};  # delete 1st key
    $h_diff{a} = 1;                   # replace with "a" key
    are_hashes_equal( $h, \%h_diff ) == 0;
}, name => "differences in values of keys are detected";

Property {
    ##[ h <- Hash( Int, Int, length=>[1,] ) ]##
    my %h_diff = %$h;
    $h_diff{scalar each %$h}++;  # increment 1st value
    are_hashes_equal( $h, \%h_diff ) == 0;
}, name => "differences in values are detected";