difference.sift.lua

type Set<T> = { [T]: true }

-- Asymmetric difference 
local function difference<V>(set: Set<V>, ...: Set<V>): Set<V>
  local diff = table.clone(set)

  for index, nextSet in { ... } do
    for value in nextSet do
      diff[value] = nil
    end
  end

  return diff
end

-- Symmetric difference
local function differenceSymmetric<V>(set: Set<V>, ...: Set<V>): Set<V>
  local diff = table.clone(set)

  for _, nextSet in { ... } do
    for value in nextSet do
      diff[value] = if diff[value] == nil then true else false
    end
  end

  for value, keep in diff do
    diff[value] = if keep then true else nil
  end

  return diff
end