NAME

FP::HashSet - set operations for hash tables

SYNOPSIS

    use FP::Equal 'is_equal';
    use FP::HashSet; # ":all";

    my $A= array_to_hashset ["a","b","c"];
    my $B= array_to_hashset ["a","c","d"];
    is_equal hashset_to_array hashset_union($A,$B),
             ["a","b","c","d"];
    is_equal hashset_to_array hashset_intersection($A,$B),
             ["a","c"];
    is_equal hashset_to_array hashset_difference($A,$B),
             ["b"];
    ok not hashset_is_subset($B,$A);
    ok hashset_is_subset(+{b=>1},$A);
    is hashset_size($A), 3;
    ok not hashset_empty($A);
    ok hashset_empty(+{});
    #hashset_keys_unsorted($A) # ("a","b","c") or in another sort order;
                               # *keys* not values, hence always strings.
    is_equal [hashset_keys ($A)],
             [("a","b","c")]; # (always sorted)

    # a la diff tool:
    is_equal hashset_diff($A,$B), +{ b=>"-", d=>"+" };

    # to treat a hashset as a function:
    my $f= hashset_to_predicate ($A);
    ok $f->("a");

DESCRIPTION

Hashsets are hash tables that are expected to have keys representing the values unambiguously (FP::Array::array_to_hashset will just use the stringification).

Note that hashset_to_array will use the *values* of the hashes, not the keys.