Class-Based Set Module

local set = {}

--create a nil set;
function set.create()
    return setmetatable({}, set)
end

--insert a x value in set s;
function set:insert(x)
    self[x] = true
end

--remove a x value of set s;
function set:remove(x)
    self[x] = nil
end

--create and return a complement set
function set:complement(s2)
    local s3 = set.create()
    for k in pairs(s2) do
        if not self:isIn(k) then
            s3:insert(k)
        end
    end
    return s3
end

--create and return the unite two sets
function set:union(s2)
    local s3 = set.create()
    for k in pairs(self) do
        s3:insert(k)
    end
    for k in pairs(s2) do
        s3:insert(k)
    end
    return s3
end

--create and return the intersection of two sets
function set:intersection(s2)
    local s3 = set.create()
    for k in pairs(self) do
        if s2:isIn(k) then
            s3:insert(k)
        end
    end
    return s3
end

--return true if the set s is nil
function set:isEmpty()
    local count = 0
    for k in pairs(self) do
        count = count + 1
    end
    return count == 0
end

--return true if x is in set s
function set:isIn(self, x)
    return self[x]
end

--return true if s2 is contained in s1
function set:isSubset(s2)
    for k in pairs(s2) do
        if not self:isIn(k) then
            return false
        end
    end
    return true
end

--return true if s1 is contained in s2
function set:isSuperset(s2)
    return s2:isSubset(self)
end

return set