first draft

Inital working version in version control

Set.lua

@@ -0,0 +1,87 @@
+local Set = {}
+Set.mt = {__index = Set}
+function Set:new(t)
+  local instance = {}
+  if type(t) == "table" then
+    if #t > 0 then
+      for _,v in ipairs(t) do
+        instance[v] = true
+      end
+    else
+      for k in pairs(t) do
+        instance[k] = true
+      end
+    end
+  else
+    instance = {t}
+  end
+  return setmetatable(instance, Set.mt)
+end
+
+function Set:add(e)
+  self[e] = true
+end
+
+function Set:remove(e)
+  self[e] = nil
+end
+
+-- Union
+Set.mt.__add = function (a, b)
+  local res = Set:new()
+  if getmetatable(a) ~= Set.mt then a = Set:new(a) end
+  if getmetatable(b) ~= Set.mt then b = Set:new(b) end
+  for k in pairs(a) do res[k] = true end
+  for k in pairs(b) do res[k] = true end
+  return res
+end
+
+-- Subtraction
+Set.mt.__sub = function (a, b)
+  local res = Set:new()
+  if getmetatable(a) ~= Set.mt then a = Set:new(a) end
+  if getmetatable(b) ~= Set.mt then b = Set:new(b) end
+  for k in pairs(a) do res[k] = true end
+  for k in pairs(b) do res[k] = nil end
+  return res
+end
+
+-- Intersection
+Set.mt.__mul = function (a, b)
+  local res = Set:new()
+  if getmetatable(a) ~= Set.mt then a = Set:new(a) end
+  if getmetatable(b) ~= Set.mt then b = Set:new(b) end
+  for k in pairs(a) do
+    res[k] = b[k]
+  end
+  return res
+end
+
+-- String representation
+Set.mt.__tostring = function (set)
+  local s = "{"
+  local sep = ""
+  for k in pairs(set) do
+    s = s .. sep .. k
+    sep = ", "
+  end
+  return s .. "}"
+end
+
+function Set:len()
+  local num = 0
+  for _ in pairs(self) do
+    num = num + 1
+  end
+  return num
+end
+
+function Set:tolist()
+  local res = {}
+  for k in pairs(self) do
+    table.insert(res, k)
+  end
+  return res
+end
+
+return Set