June 2018 Update

Task/Set/Lua/set-2.lua

@@ -0,0 +1,111 @@
+local function new(_, ...)
+  local r = {}
+  local s = setmetatable({}, {
+    -- API operations
+    __index = {
+
+      -- single value insertion
+      insert = function(s, v)
+        if not r[v] then
+          table.insert(s, v)
+          r[v] = #s
+        end
+        return s
+      end,
+
+      -- single value removal
+      remove = function(s, v)
+        local i = r[v]
+        if i then
+          r[v] = nil
+          local t = table.remove(s)
+          if t ~= v then
+            r[t] = i
+            s[i] = t
+          end
+        end
+        return s
+      end,
+
+      -- multi-value insertion
+      batch_insert = function(s, ...)
+        for _,v in pairs {...} do
+          s:insert(v)
+        end
+        return s
+      end,
+
+      -- multi-value removal
+      batch_remove = function(s, ...)
+        for _,v in pairs {...} do
+          s:remove(v)
+        end
+        return s
+      end,
+
+      -- membership test
+      has = function(s, e)
+        return r[e] ~= nil
+      end
+    },
+
+    -- set manipulation operators
+
+    -- union
+    __add = function(s1, s2)
+      r = set()
+      r:batch_insert(table.unpack(s1))
+      r:batch_insert(table.unpack(s2))
+      return r
+    end,
+
+    -- subtraction
+    __sub = function(s1, s2)
+      r = set()
+      r:batch_insert(table.unpack(s1))
+      r:batch_remove(table.unpack(s2))
+      return r
+    end,
+
+    -- intersection
+    __mul = function(s1, s2)
+      r = set()
+      for _,v in ipairs(s1) do
+        if s2:has(v) then
+          r:insert(v)
+        end
+      end
+      return r
+    end,
+
+    -- equality
+    __eq = function(s1, s2)
+      if #s1 ~= #s2 then return false end
+      for _,v in ipairs(s1) do
+        if not s2:has(v) then return false end
+      end
+      return true
+    end,
+
+    -- proper subset
+    __lt = function(s1, s2)
+      if s1 == s2 then return false end
+      for _,v in ipairs(s1) do
+        if not s2:has(v) then return false end
+      end
+      return true
+    end,
+
+    -- subset
+    __lte = function(s1, s2)
+      return (s1 == s2) or (s1 < s2)
+    end,
+
+    -- metatable type tag
+    __type__ = 'set'
+  })
+  s:batch_insert(...)
+  return s
+end
+
+return setmetatable({}, { __call = new })