#!/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";