diff --git a/core/control_flow.nom b/core/control_flow.nom
index 4066a97..d40c349 100644
--- a/core/control_flow.nom
+++ b/core/control_flow.nom
@@ -88,7 +88,7 @@ immediately:
             locals: %body_lua's "locals"
             statements:".."
                 for \(%subtree as lua expr) in coroutine.wrap(function() nomsu:walk_tree(\(%tree as lua expr)) end) do
-                    if type(\(%subtree as lua expr)) == 'table' and \(%subtree as lua expr).type then
+                    if Types.is_node(\(%subtree as lua expr)) then
                         if \(%condition as lua expr) then
                             \%body_statements
                             break;
diff --git a/core/operators.nom b/core/operators.nom
index d2929bf..7a6f535 100644
--- a/core/operators.nom
+++ b/core/operators.nom
@@ -79,7 +79,7 @@ immediately:
             Expected a Dict for the assignments part of '<- %' statement, not \(%assignments' source code)
         lua> ".."
             for i, item in ipairs(\%assignments.value) do
-                local target, value = item.dict_key, item.dict_value;
+                local target, value = item.key, item.value;
                 local target_lua = nomsu:tree_to_lua(target);
                 if not target_lua.expr then error("Invalid target for assignment: "..target:get_src()); end
                 local value_lua = nomsu:tree_to_lua(value);
diff --git a/nomsu.lua b/nomsu.lua
index 90188ad..0ea6078 100644
--- a/nomsu.lua
+++ b/nomsu.lua
@@ -3,6 +3,7 @@ local re = require('re')
 local lpeg = require('lpeg')
 local utils = require('utils')
 local new_uuid = require('uuid')
+local immutable = require('immutable')
 local repr, stringify, min, max, equivalent, set, is_list, sum
 repr, stringify, min, max, equivalent, set, is_list, sum = utils.repr, utils.stringify, utils.min, utils.max, utils.equivalent, utils.set, utils.is_list, utils.sum
 local colors = setmetatable({ }, {
@@ -22,6 +23,14 @@ do
   local _obj_0 = table
   insert, remove, concat = _obj_0.insert, _obj_0.remove, _obj_0.concat
 end
+local _tuples = { }
+local Tuple
+Tuple = function(t)
+  if not _tuples[#t] then
+    _tuples[#t] = immutable(#t)
+  end
+  return _tuples[#t]:from_table(t)
+end
 local cached
 cached = function(fn)
   local cache = setmetatable({ }, {
@@ -52,9 +61,46 @@ end
 lpeg.setmaxstack(10000)
 local P, R, V, S, Cg, C, Cp, B, Cmt
 P, R, V, S, Cg, C, Cp, B, Cmt = lpeg.P, lpeg.R, lpeg.V, lpeg.S, lpeg.Cg, lpeg.C, lpeg.Cp, lpeg.B, lpeg.Cmt
+local Types = { }
+local _list_0 = {
+  "File",
+  "Nomsu",
+  "Block",
+  "List",
+  "FunctionCall",
+  "Text",
+  "Dict",
+  "Number",
+  "Word",
+  "Var",
+  "Comment"
+}
+for _index_0 = 1, #_list_0 do
+  local t = _list_0[_index_0]
+  Types[t] = immutable({
+    "id",
+    "value"
+  }, {
+    type = t,
+    name = t
+  })
+end
+Types.DictEntry = immutable({
+  "key",
+  "value"
+}, {
+  name = "DictEntry"
+})
+Types.is_node = function(n)
+  return type(n) == 'userdata' and n.type
+end
 local NOMSU_DEFS
 do
   local _with_0 = { }
+  _with_0.Tuple = Tuple
+  _with_0.DictEntry = function(k, v)
+    return Types.DictEntry(k, v)
+  end
   _with_0.nl = P("\r") ^ -1 * P("\n")
   _with_0.ws = S(" \t")
   _with_0.tonumber = tonumber
@@ -133,14 +179,16 @@ do
   end
   NOMSU_DEFS = _with_0
 end
+local node_id = 0
 setmetatable(NOMSU_DEFS, {
   __index = function(self, key)
     local make_node
     make_node = function(start, value, stop)
-      local node = {
-        type = key,
-        value = value
-      }
+      node_id = node_id + 1
+      if type(value) == 'table' then
+        error(value)
+      end
+      local node = Types[key](node_id, value)
       lpeg.userdata.tree_metadata[node] = {
         start = start,
         stop = stop,
@@ -490,7 +538,7 @@ do
         expr_type = nil
       end
       assert(tree, "No tree provided to tree_to_nomsu.")
-      assert(tree.type, "Invalid tree: " .. tostring(repr(tree)))
+      assert(Types.is_node(tree), "Invalid tree: " .. tostring(repr(tree)))
       local join_lines
       join_lines = function(lines)
         for _index_0 = 1, #lines do
@@ -543,9 +591,9 @@ do
           return buff
         elseif "List" == _exp_0 then
           local bits = { }
-          local _list_0 = tok.value
-          for _index_0 = 1, #_list_0 do
-            local bit = _list_0[_index_0]
+          local _list_1 = tok.value
+          for _index_0 = 1, #_list_1 do
+            local bit = _list_1[_index_0]
             local nomsu = inline_expression(bit)
             if not (nomsu) then
               return nil
@@ -555,22 +603,22 @@ do
           return "[" .. concat(bits, ", ") .. "]"
         elseif "Dict" == _exp_0 then
           local bits = { }
-          local _list_0 = tok.value
-          for _index_0 = 1, #_list_0 do
-            local bit = _list_0[_index_0]
+          local _list_1 = tok.value
+          for _index_0 = 1, #_list_1 do
+            local bit = _list_1[_index_0]
             local key_nomsu
-            if bit.dict_key.type == "Word" then
-              key_nomsu = bit.dict_key.value
+            if bit.key.type == "Word" then
+              key_nomsu = bit.key.value
             else
-              key_nomsu = inline_expression(bit.dict_key)
+              key_nomsu = inline_expression(bit.key)
             end
             if not (key_nomsu) then
               return nil
             end
-            if bit.dict_key.type == "FunctionCall" then
+            if bit.key.type == "FunctionCall" then
               key_nomsu = "(" .. key_nomsu .. ")"
             end
-            local value_nomsu = inline_expression(bit.dict_value)
+            local value_nomsu = inline_expression(bit.value)
             if not (value_nomsu) then
               return nil
             end
@@ -579,9 +627,9 @@ do
           return "{" .. concat(bits, ", ") .. "}"
         elseif "Text" == _exp_0 then
           local buff = '"'
-          local _list_0 = tok.value
-          for _index_0 = 1, #_list_0 do
-            local bit = _list_0[_index_0]
+          local _list_1 = tok.value
+          for _index_0 = 1, #_list_1 do
+            local bit = _list_1[_index_0]
             if type(bit) == 'string' then
               if bit:find("\n") then
                 return nil
@@ -627,9 +675,9 @@ do
         local _exp_0 = tok.type
         if "Block" == _exp_0 then
           local buff = ":"
-          local _list_0 = tok.value
-          for _index_0 = 1, #_list_0 do
-            local line = _list_0[_index_0]
+          local _list_1 = tok.value
+          for _index_0 = 1, #_list_1 do
+            local line = _list_1[_index_0]
             nomsu = expression(line)
             if not (nomsu) then
               return nil
@@ -646,9 +694,9 @@ do
         elseif "List" == _exp_0 then
           local buff = "[..]"
           local line = "\n    "
-          local _list_0 = tok.value
-          for _index_0 = 1, #_list_0 do
-            local bit = _list_0[_index_0]
+          local _list_1 = tok.value
+          for _index_0 = 1, #_list_1 do
+            local bit = _list_1[_index_0]
             nomsu = inline_expression(bit)
             if line ~= "\n    " and #line + #", " + #nomsu > max_line then
               buff = buff .. line
@@ -674,17 +722,17 @@ do
         elseif "Dict" == _exp_0 then
           local buff = "{..}"
           local line = "\n    "
-          local _list_0 = tok.value
-          for _index_0 = 1, #_list_0 do
-            local bit = _list_0[_index_0]
-            local key_nomsu = inline_expression(bit.dict_key)
+          local _list_1 = tok.value
+          for _index_0 = 1, #_list_1 do
+            local bit = _list_1[_index_0]
+            local key_nomsu = inline_expression(bit.key)
             if not (key_nomsu) then
               return nil
             end
-            if bit.dict_key.type == "FunctionCall" then
+            if bit.key.type == "FunctionCall" then
               key_nomsu = "(" .. key_nomsu .. ")"
             end
-            local value_nomsu = inline_expression(bit.dict_value)
+            local value_nomsu = inline_expression(bit.value)
             if value_nomsu and #key_nomsu + #value_nomsu < max_line then
               line = line .. (key_nomsu .. "=" .. value_nomsu .. ",")
               if #line >= max_line then
@@ -692,7 +740,7 @@ do
                 line = "\n    "
               end
             else
-              line = line .. (key_nomsu .. "=" .. expression(bit.dict_value))
+              line = line .. (key_nomsu .. "=" .. expression(bit.value))
               buff = buff .. line
               line = "\n    "
             end
@@ -703,9 +751,9 @@ do
           return buff
         elseif "Text" == _exp_0 then
           local buff = '".."\n    '
-          local _list_0 = tok.value
-          for _index_0 = 1, #_list_0 do
-            local bit = _list_0[_index_0]
+          local _list_1 = tok.value
+          for _index_0 = 1, #_list_1 do
+            local bit = _list_1[_index_0]
             if type(bit) == 'string' then
               buff = buff .. bit:gsub("\\", "\\\\"):gsub("\n", "\n    ")
             else
@@ -793,9 +841,9 @@ do
           return buff
         elseif "File" == _exp_0 then
           local lines = { }
-          local _list_0 = tree.value
-          for _index_0 = 1, #_list_0 do
-            local line = _list_0[_index_0]
+          local _list_1 = tree.value
+          for _index_0 = 1, #_list_1 do
+            local line = _list_1[_index_0]
             nomsu = expression(line)
             if not (nomsu) then
               local src = self:get_source_code(line)
@@ -861,7 +909,7 @@ do
     end,
     tree_to_lua = function(self, tree)
       assert(tree, "No tree provided.")
-      if not tree.type then
+      if not Types.is_node(tree) then
         error("Invalid tree: " .. tostring(repr(tree)), 0)
       end
       local _exp_0 = tree.type
@@ -872,9 +920,9 @@ do
         local declared_locals = { }
         local lua_bits = { }
         local line_no = 1
-        local _list_0 = tree.value
-        for _index_0 = 1, #_list_0 do
-          local line = _list_0[_index_0]
+        local _list_1 = tree.value
+        for _index_0 = 1, #_list_1 do
+          local line = _list_1[_index_0]
           local lua = self:tree_to_lua(line)
           if not lua then
             error("No lua produced by " .. tostring(repr(line)), 0)
@@ -884,9 +932,9 @@ do
             do
               local _accum_0 = { }
               local _len_0 = 1
-              local _list_1 = lua.locals
-              for _index_1 = 1, #_list_1 do
-                local l = _list_1[_index_1]
+              local _list_2 = lua.locals
+              for _index_1 = 1, #_list_2 do
+                local l = _list_2[_index_1]
                 if not declared_locals[l] then
                   _accum_0[_len_0] = l
                   _len_0 = _len_0 + 1
@@ -922,9 +970,9 @@ do
       elseif "Block" == _exp_0 then
         local lua_bits = { }
         local locals = { }
-        local _list_0 = tree.value
-        for _index_0 = 1, #_list_0 do
-          local arg = _list_0[_index_0]
+        local _list_1 = tree.value
+        for _index_0 = 1, #_list_1 do
+          local arg = _list_1[_index_0]
           local lua = self:tree_to_lua(arg)
           if #tree.value == 1 and lua.expr and not lua.statements then
             return {
@@ -933,9 +981,9 @@ do
             }
           end
           if lua.locals then
-            local _list_1 = lua.locals
-            for _index_1 = 1, #_list_1 do
-              local l = _list_1[_index_1]
+            local _list_2 = lua.locals
+            for _index_1 = 1, #_list_2 do
+              local l = _list_2[_index_1]
               table.insert(locals, l)
             end
           end
@@ -965,9 +1013,9 @@ do
           do
             local _accum_0 = { }
             local _len_0 = 1
-            local _list_0 = tree.value
-            for _index_0 = 1, #_list_0 do
-              local arg = _list_0[_index_0]
+            local _list_1 = tree.value
+            for _index_0 = 1, #_list_1 do
+              local arg = _list_1[_index_0]
               if arg.type ~= "Word" then
                 _accum_0[_len_0] = arg
                 _len_0 = _len_0 + 1
@@ -980,9 +1028,9 @@ do
             do
               local _accum_0 = { }
               local _len_0 = 1
-              local _list_0 = metadata.arg_orders[stub]
-              for _index_0 = 1, #_list_0 do
-                local p = _list_0[_index_0]
+              local _list_1 = metadata.arg_orders[stub]
+              for _index_0 = 1, #_list_1 do
+                local p = _list_1[_index_0]
                 _accum_0[_len_0] = args[p]
                 _len_0 = _len_0 + 1
               end
@@ -1008,9 +1056,9 @@ do
           return lua
         elseif not metadata and self.__class.math_patt:match(stub) then
           local bits = { }
-          local _list_0 = tree.value
-          for _index_0 = 1, #_list_0 do
-            local tok = _list_0[_index_0]
+          local _list_1 = tree.value
+          for _index_0 = 1, #_list_1 do
+            local tok = _list_1[_index_0]
             if tok.type == "Word" then
               insert(bits, tok.value)
             else
@@ -1028,11 +1076,11 @@ do
           }
         end
         local args = { }
-        local _list_0 = tree.value
-        for _index_0 = 1, #_list_0 do
+        local _list_1 = tree.value
+        for _index_0 = 1, #_list_1 do
           local _continue_0 = false
           repeat
-            local tok = _list_0[_index_0]
+            local tok = _list_1[_index_0]
             if tok.type == "Word" then
               _continue_0 = true
               break
@@ -1055,9 +1103,9 @@ do
           do
             local _accum_0 = { }
             local _len_0 = 1
-            local _list_1 = metadata.arg_orders[stub]
-            for _index_0 = 1, #_list_1 do
-              local p = _list_1[_index_0]
+            local _list_2 = metadata.arg_orders[stub]
+            for _index_0 = 1, #_list_2 do
+              local p = _list_2[_index_0]
               _accum_0[_len_0] = args[p]
               _len_0 = _len_0 + 1
             end
@@ -1072,11 +1120,11 @@ do
       elseif "Text" == _exp_0 then
         local concat_parts = { }
         local string_buffer = ""
-        local _list_0 = tree.value
-        for _index_0 = 1, #_list_0 do
+        local _list_1 = tree.value
+        for _index_0 = 1, #_list_1 do
           local _continue_0 = false
           repeat
-            local bit = _list_0[_index_0]
+            local bit = _list_1[_index_0]
             if type(bit) == "string" then
               string_buffer = string_buffer .. bit
               _continue_0 = true
@@ -1122,9 +1170,9 @@ do
         end
       elseif "List" == _exp_0 then
         local items = { }
-        local _list_0 = tree.value
-        for _index_0 = 1, #_list_0 do
-          local item = _list_0[_index_0]
+        local _list_1 = tree.value
+        for _index_0 = 1, #_list_1 do
+          local item = _list_1[_index_0]
           local lua = self:tree_to_lua(item)
           if not (lua.expr) then
             local line = self:get_line_number(item)
@@ -1138,26 +1186,26 @@ do
         }
       elseif "Dict" == _exp_0 then
         local items = { }
-        local _list_0 = tree.value
-        for _index_0 = 1, #_list_0 do
-          local entry = _list_0[_index_0]
+        local _list_1 = tree.value
+        for _index_0 = 1, #_list_1 do
+          local entry = _list_1[_index_0]
           local key_lua
-          if entry.dict_key.type == "Word" then
+          if entry.key.type == "Word" then
             key_lua = {
-              expr = repr(entry.dict_key.value)
+              expr = repr(entry.key.value)
             }
           else
-            key_lua = self:tree_to_lua(entry.dict_key)
+            key_lua = self:tree_to_lua(entry.key)
           end
           if not (key_lua.expr) then
-            local line = self:get_line_number(entry.dict_key)
-            local src = self:get_source_code(entry.dict_key)
+            local line = self:get_line_number(entry.key)
+            local src = self:get_source_code(entry.key)
             error(tostring(line) .. ": Cannot use " .. tostring(colored.yellow(src)) .. " as a dict key, since it's not an expression.", 0)
           end
-          local value_lua = self:tree_to_lua(entry.dict_value)
+          local value_lua = self:tree_to_lua(entry.value)
           if not (value_lua.expr) then
-            local line = self:get_line_number(entry.dict_value)
-            local src = self:get_source_code(entry.dict_value)
+            local line = self:get_line_number(entry.value)
+            local src = self:get_source_code(entry.value)
             error(tostring(line) .. ": Cannot use " .. tostring(colored.yellow(src)) .. " as a dict value, since it's not an expression.", 0)
           end
           local key_str = key_lua.expr:match([=[["']([a-zA-Z_][a-zA-Z0-9_]*)['"]]=])
@@ -1189,22 +1237,22 @@ do
         depth = 0
       end
       coroutine.yield(tree, depth)
-      if type(tree) ~= 'table' or not tree.type then
+      if not (Types.is_node(tree)) then
         return 
       end
       local _exp_0 = tree.type
       if "List" == _exp_0 or "File" == _exp_0 or "Block" == _exp_0 or "FunctionCall" == _exp_0 or "Text" == _exp_0 then
-        local _list_0 = tree.value
-        for _index_0 = 1, #_list_0 do
-          local v = _list_0[_index_0]
+        local _list_1 = tree.value
+        for _index_0 = 1, #_list_1 do
+          local v = _list_1[_index_0]
           self:walk_tree(v, depth + 1)
         end
       elseif "Dict" == _exp_0 then
-        local _list_0 = tree.value
-        for _index_0 = 1, #_list_0 do
-          local e = _list_0[_index_0]
-          self:walk_tree(e.dict_key, depth + 1)
-          self:walk_tree(e.dict_value, depth + 1)
+        local _list_1 = tree.value
+        for _index_0 = 1, #_list_1 do
+          local e = _list_1[_index_0]
+          self:walk_tree(e.key, depth + 1)
+          self:walk_tree(e.value, depth + 1)
         end
       else
         self:walk_tree(tree.value, depth + 1)
@@ -1216,10 +1264,10 @@ do
       for node, depth in coroutine.wrap(function()
         return self:walk_tree(tree)
       end) do
-        if type(node) ~= 'table' or not node.type then
-          print(("    "):rep(depth) .. repr(node))
-        else
+        if Types.is_node(node) then
           print(tostring(("    "):rep(depth)) .. tostring(node.type) .. ":")
+        else
+          print(("    "):rep(depth) .. repr(node))
         end
       end
       return io.write(colors.reset)
@@ -1229,16 +1277,16 @@ do
       for node, depth in coroutine.wrap(function()
         return self:walk_tree(tree)
       end) do
-        if type(node) ~= 'table' or not node.type then
-          insert(bits, (("    "):rep(depth) .. repr(node)))
-        else
+        if Types.is_node(node) then
           insert(bits, (tostring(("    "):rep(depth)) .. tostring(node.type) .. ":"))
+        else
+          insert(bits, (("    "):rep(depth) .. repr(node)))
         end
       end
       return concat(bits, "\n")
     end,
     tree_map = function(self, tree, fn)
-      if type(tree) ~= 'table' then
+      if not (Types.is_node(tree)) then
         return tree
       end
       local replacement = fn(tree)
@@ -1258,44 +1306,25 @@ do
           end
         end
         if is_changed then
-          local new_tree
-          do
-            local _tbl_0 = { }
-            for k, v in pairs(tree) do
-              _tbl_0[k] = v
-            end
-            new_tree = _tbl_0
-          end
+          local new_tree = getmetatable(tree)(tree.id, Tuple(new_values))
           self.tree_metadata[new_tree] = self.tree_metadata[tree]
-          new_tree.value = new_values
           return new_tree
         end
       elseif "Dict" == _exp_0 then
         local new_values, is_changed = { }, false
         for i, e in ipairs(tree.value) do
-          local new_key = self:tree_map(e.dict_key, fn)
-          local new_value = self:tree_map(e.dict_value, fn)
-          if (new_key ~= nil and new_key ~= e.dict_key) or (new_value ~= nil and new_value ~= e.dict_value) then
+          local new_key = self:tree_map(e.key, fn)
+          local new_value = self:tree_map(e.value, fn)
+          if (new_key ~= nil and new_key ~= e.key) or (new_value ~= nil and new_value ~= e.value) then
             is_changed = true
-            new_values[i] = {
-              dict_key = new_key,
-              dict_value = new_value
-            }
+            new_values[i] = DictEntry(new_key, new_value)
           else
             new_values[i] = e
           end
         end
         if is_changed then
-          local new_tree
-          do
-            local _tbl_0 = { }
-            for k, v in pairs(tree) do
-              _tbl_0[k] = v
-            end
-            new_tree = _tbl_0
-          end
+          local new_tree = getmetatable(tree)(tree.id, Tuple(new_values))
           self.tree_metadata[new_tree] = self.tree_metadata[tree]
-          new_tree.value = new_values
           return new_tree
         end
       elseif nil == _exp_0 then
@@ -1320,9 +1349,9 @@ do
       return concat((function()
         local _accum_0 = { }
         local _len_0 = 1
-        local _list_0 = tree.value
-        for _index_0 = 1, #_list_0 do
-          local t = _list_0[_index_0]
+        local _list_1 = tree.value
+        for _index_0 = 1, #_list_1 do
+          local t = _list_1[_index_0]
           _accum_0[_len_0] = (t.type == "Word" and t.value or "%")
           _len_0 = _len_0 + 1
         end
@@ -1336,9 +1365,9 @@ do
       return concat((function()
         local _accum_0 = { }
         local _len_0 = 1
-        local _list_0 = tree.value
-        for _index_0 = 1, #_list_0 do
-          local t = _list_0[_index_0]
+        local _list_1 = tree.value
+        for _index_0 = 1, #_list_1 do
+          local t = _list_1[_index_0]
           _accum_0[_len_0] = (t.type == "Word" and t.value or "%" .. tostring(t.value))
           _len_0 = _len_0 + 1
         end
@@ -1382,7 +1411,7 @@ do
       return stub_args
     end,
     var_to_lua_identifier = function(self, var)
-      if type(var) == 'table' and var.type == "Var" then
+      if Types.Var:is_instance(var) then
         var = var.value
       end
       return "_" .. (var:gsub("%W", function(verboten)
@@ -1402,9 +1431,9 @@ do
       local nomsu_string_as_lua
       nomsu_string_as_lua = function(code)
         local concat_parts = { }
-        local _list_0 = code.value
-        for _index_0 = 1, #_list_0 do
-          local bit = _list_0[_index_0]
+        local _list_1 = code.value
+        for _index_0 = 1, #_list_1 do
+          local bit = _list_1[_index_0]
           if type(bit) == "string" then
             insert(concat_parts, bit)
           else
@@ -1548,6 +1577,7 @@ do
         end
       })
       self.environment.LOADED = { }
+      self.environment.Types = Types
       return self:initialize_core()
     end,
     __base = _base_0,
diff --git a/nomsu.moon b/nomsu.moon
index df6d296..037368b 100755
--- a/nomsu.moon
+++ b/nomsu.moon
@@ -15,11 +15,18 @@ re = require 're'
 lpeg = require 'lpeg'
 utils = require 'utils'
 new_uuid = require 'uuid'
+immutable = require 'immutable'
 {:repr, :stringify, :min, :max, :equivalent, :set, :is_list, :sum} = utils
 colors = setmetatable({}, {__index:->""})
 colored = setmetatable({}, {__index:(_,color)-> ((msg)-> colors[color]..(msg or '')..colors.reset)})
 {:insert, :remove, :concat} = table
 
+_tuples = {}
+Tuple = (t)->
+    if not _tuples[#t]
+        _tuples[#t] = immutable(#t)
+    return _tuples[#t]\from_table(t)
+
 cached = (fn)->
     cache = setmetatable({}, {__mode:"k"})
     return (self, arg)->
@@ -53,8 +60,17 @@ do
 lpeg.setmaxstack 10000 -- whoa
 {:P,:R,:V,:S,:Cg,:C,:Cp,:B,:Cmt} = lpeg
 
+Types = {}
+for t in *{"File", "Nomsu", "Block", "List", "FunctionCall", "Text", "Dict", "Number", "Word", "Var", "Comment"}
+    Types[t] = immutable({"id","value"}, {type:t, name:t})
+Types.DictEntry = immutable({"key","value"}, {name:"DictEntry"})
+Types.is_node = (n)->
+    type(n) == 'userdata' and n.type
+
 NOMSU_DEFS = with {}
     -- Newline supports either windows-style CR+LF or unix-style LF
+    .Tuple = Tuple
+    .DictEntry = (k,v) -> Types.DictEntry(k,v)
     .nl = P("\r")^-1 * P("\n")
     .ws = S(" \t")
     .tonumber = tonumber
@@ -114,9 +130,12 @@ NOMSU_DEFS = with {}
         err_msg ..="\n#{prev_line}\n#{err_line}\n#{pointer}\n#{next_line}\n"
         error(err_msg)
 
+node_id = 0
 setmetatable(NOMSU_DEFS, {__index:(key)=>
     make_node = (start, value, stop)->
-        node = {type: key, :value}
+        node_id = node_id + 1
+        if type(value) == 'table' then error(value)-- = Tuple(value)
+        node = Types[key](node_id, value)
         lpeg.userdata.tree_metadata[node] = {
             :start,:stop,filename:lpeg.userdata.filename,source_code:lpeg.userdata.source_code
         }
@@ -176,6 +195,7 @@ class NomsuCompiler
             error("Attempt to run undefined action: #{key}", 0)
         })
         @environment.LOADED = {}
+        @environment.Types = Types
         @initialize_core!
     
     define_action: (signature, source, fn)=>
@@ -394,7 +414,7 @@ class NomsuCompiler
         --   "inline" for code that cannot contain indented code or an end-of-line component
         --       e.g. code that is meant to go inside parentheses
         assert tree, "No tree provided to tree_to_nomsu."
-        assert tree.type, "Invalid tree: #{repr(tree)}"
+        assert Types.is_node(tree), "Invalid tree: #{repr(tree)}"
         join_lines = (lines)->
             for line in *lines
                 if #indentation + #line > max_line
@@ -436,13 +456,13 @@ class NomsuCompiler
                 when "Dict"
                     bits = {}
                     for bit in *tok.value
-                        key_nomsu = if bit.dict_key.type == "Word"
-                            bit.dict_key.value
-                        else inline_expression bit.dict_key
+                        key_nomsu = if bit.key.type == "Word"
+                            bit.key.value
+                        else inline_expression bit.key
                         return nil unless key_nomsu
-                        if bit.dict_key.type == "FunctionCall"
+                        if bit.key.type == "FunctionCall"
                             key_nomsu = "("..key_nomsu..")"
-                        value_nomsu = inline_expression bit.dict_value
+                        value_nomsu = inline_expression bit.value
                         return nil unless value_nomsu
                         insert bits, key_nomsu.."="..value_nomsu
                     return "{"..concat(bits, ", ").."}"
@@ -510,18 +530,18 @@ class NomsuCompiler
                     buff = "{..}"
                     line = "\n    "
                     for bit in *tok.value
-                        key_nomsu = inline_expression bit.dict_key
+                        key_nomsu = inline_expression bit.key
                         return nil unless key_nomsu
-                        if bit.dict_key.type == "FunctionCall"
+                        if bit.key.type == "FunctionCall"
                             key_nomsu = "("..key_nomsu..")"
-                        value_nomsu = inline_expression bit.dict_value
+                        value_nomsu = inline_expression bit.value
                         if value_nomsu and #key_nomsu + #value_nomsu < max_line
                             line ..= key_nomsu.."="..value_nomsu..","
                             if #line >= max_line
                                 buff ..= line
                                 line = "\n    "
                         else
-                            line ..= key_nomsu.."="..expression(bit.dict_value)
+                            line ..= key_nomsu.."="..expression(bit.value)
                             buff ..= line
                             line = "\n    "
                     if line ~= "\n    "
@@ -638,7 +658,7 @@ class NomsuCompiler
     tree_to_lua: (tree)=>
         -- Return <lua code for value>, <additional lua code>
         assert tree, "No tree provided."
-        if not tree.type
+        if not Types.is_node(tree)
             error("Invalid tree: #{repr(tree)}", 0)
         switch tree.type
             when "File"
@@ -777,18 +797,18 @@ class NomsuCompiler
             when "Dict"
                 items = {}
                 for entry in *tree.value
-                    key_lua = if entry.dict_key.type == "Word"
-                        {expr:repr(entry.dict_key.value)}
+                    key_lua = if entry.key.type == "Word"
+                        {expr:repr(entry.key.value)}
                     else
-                        @tree_to_lua entry.dict_key
+                        @tree_to_lua entry.key
                     unless key_lua.expr
-                        line = @get_line_number(entry.dict_key)
-                        src = @get_source_code(entry.dict_key)
+                        line = @get_line_number(entry.key)
+                        src = @get_source_code(entry.key)
                         error "#{line}: Cannot use #{colored.yellow src} as a dict key, since it's not an expression.", 0
-                    value_lua = @tree_to_lua entry.dict_value
+                    value_lua = @tree_to_lua entry.value
                     unless value_lua.expr
-                        line = @get_line_number(entry.dict_value)
-                        src = @get_source_code(entry.dict_value)
+                        line = @get_line_number(entry.value)
+                        src = @get_source_code(entry.value)
                         error "#{line}: Cannot use #{colored.yellow src} as a dict value, since it's not an expression.", 0
                     key_str = key_lua.expr\match([=[["']([a-zA-Z_][a-zA-Z0-9_]*)['"]]=])
                     if key_str
@@ -810,35 +830,34 @@ class NomsuCompiler
     
     walk_tree: (tree, depth=0)=>
         coroutine.yield(tree, depth)
-        if type(tree) != 'table' or not tree.type
-            return
+        return unless Types.is_node(tree)
         switch tree.type
             when "List", "File", "Block", "FunctionCall", "Text"
                 for v in *tree.value
                     @walk_tree(v, depth+1)
             when "Dict"
                 for e in *tree.value
-                    @walk_tree(e.dict_key, depth+1)
-                    @walk_tree(e.dict_value, depth+1)
+                    @walk_tree(e.key, depth+1)
+                    @walk_tree(e.value, depth+1)
             else @walk_tree(tree.value, depth+1)
         return nil
 
     print_tree: (tree)=>
         io.write(colors.bright..colors.green)
         for node,depth in coroutine.wrap(-> @walk_tree tree)
-            if type(node) != 'table' or not node.type
-                print(("    ")\rep(depth)..repr(node))
-            else
+            if Types.is_node(node)
                 print("#{("    ")\rep(depth)}#{node.type}:")
+            else
+                print(("    ")\rep(depth)..repr(node))
         io.write(colors.reset)
     
     tree_to_str: (tree)=>
         bits = {}
         for node,depth in coroutine.wrap(-> @walk_tree tree)
-            if type(node) != 'table' or not node.type
-                insert bits, (("    ")\rep(depth)..repr(node))
-            else
+            if Types.is_node(node)
                 insert bits, ("#{("    ")\rep(depth)}#{node.type}:")
+            else
+                insert bits, (("    ")\rep(depth)..repr(node))
         return concat(bits, "\n")
 
     @unescape_string: (str)=>
@@ -860,7 +879,7 @@ class NomsuCompiler
     tree_map: (tree, fn)=>
         -- Return a new tree with fn mapped to each node. If fn provides a replacement,
         -- use that and stop recursing, otherwise recurse.
-        if type(tree) != 'table' then return tree
+        unless Types.is_node(tree) then return tree
         replacement = fn(tree)
         if replacement != nil
             return replacement
@@ -875,27 +894,25 @@ class NomsuCompiler
                     else
                         new_values[i] = old_value
                 if is_changed
-                    new_tree = {k,v for k,v in pairs(tree)}
+                    new_tree = getmetatable(tree)(tree.id, Tuple(new_values))
                     -- TODO: Maybe generate new metadata?
                     @tree_metadata[new_tree] = @tree_metadata[tree]
-                    new_tree.value = new_values
                     return new_tree
                 
             when "Dict"
                 new_values, is_changed = {}, false
                 for i,e in ipairs tree.value
-                    new_key = @tree_map(e.dict_key, fn)
-                    new_value = @tree_map(e.dict_value, fn)
-                    if (new_key != nil and new_key != e.dict_key) or (new_value != nil and new_value != e.dict_value)
+                    new_key = @tree_map(e.key, fn)
+                    new_value = @tree_map(e.value, fn)
+                    if (new_key != nil and new_key != e.key) or (new_value != nil and new_value != e.value)
                         is_changed = true
-                        new_values[i] = {dict_key:new_key, dict_value:new_value}
+                        new_values[i] = DictEntry(new_key, new_value)
                     else
                         new_values[i] = e
                 if is_changed
-                    new_tree = {k,v for k,v in pairs(tree)}
+                    new_tree = getmetatable(tree)(tree.id, Tuple(new_values))
                     -- TODO: Maybe generate new metadata?
                     @tree_metadata[new_tree] = @tree_metadata[tree]
-                    new_tree.value = new_values
                     return new_tree
             when nil -- Raw table, probably from one of the .value of a multi-value tree (e.g. List)
                 error("Invalid tree: #{repr tree}")
@@ -953,7 +970,7 @@ class NomsuCompiler
     var_to_lua_identifier: (var)=>
         -- Converts arbitrary nomsu vars to valid lua identifiers by replacing illegal
         -- characters with escape sequences
-        if type(var) == 'table' and var.type == "Var"
+        if Types.Var\is_instance(var)
             var = var.value
         "_"..(var\gsub "%W", (verboten)->
             if verboten == "_" then "__" else ("_%x")\format(verboten\byte!))
diff --git a/nomsu.peg b/nomsu.peg
index 6c12cc4..bfa9f0c 100644
--- a/nomsu.peg
+++ b/nomsu.peg
@@ -3,7 +3,7 @@ file (File):
         (ignored_line %nl)*
         statement (nodent statement)*
         (%nl ignored_line)*
-    (!. / (("" -> "Parse error") => error)?) |}
+    (!. / (("" -> "Parse error") => error)?) |} -> Tuple
 
 shebang: "#!" [^%nl]* %nl
 
@@ -13,7 +13,7 @@ indented_block (Block):
     {| (":" / "(..)")? indent
             statement (nodent statement)*
         (dedent / (("" -> "Error while parsing block") => error))
-    |}
+    |} -> Tuple
 
 inline_nomsu (Nomsu): "\" inline_expression
 indented_nomsu (Nomsu): "\" expression
@@ -29,27 +29,27 @@ expression:
 -- Function calls need at least one word in them
 inline_functioncall (FunctionCall):
     {| (inline_expression %ws*)* word (%ws* (inline_expression / word))*
-        (%ws* ":" %ws* (inline_functioncall / inline_expression))?|}
+        (%ws* ":" %ws* (inline_functioncall / inline_expression))?|} -> Tuple
 functioncall (FunctionCall):
-    {| (expression (dotdot / %ws*))* word ((dotdot / %ws*) (expression / word))* |}
+    {| (expression (dotdot / %ws*))* word ((dotdot / %ws*) (expression / word))* |} -> Tuple
 
 word (Word): { %operator / (!number plain_word) }
 
 inline_text (Text):
     !('".."' eol)
-    '"' {|
+    '"' ({|
         ({~ (('\"' -> '"') / ('\\' -> '\') / %escaped_char / [^%nl\"])+ ~}
         / inline_text_interpolation)*
-    |} '"'
+    |} -> Tuple) '"'
 -- Have to use "%indent" instead of "indent" etc. to avoid messing up text lines that start with "#"
 indented_text (Text):
-    '".."' eol %nl {|
+    '".."' eol %nl ({|
         {~ (%nl*) (%indent -> "") ~}
         ({~
             (("\\" -> "\") / (("\" eol %nl+ %nodent "..") -> "")
             / (%nl+ {~ %nodent -> "" ~}) / [^%nl\])+
         ~} / text_interpolation)*
-    |} (((!.) &%dedent) / (&(%nl %dedent)) / (("" -> "Error while parsing Text") => error))
+    |} -> Tuple) (((!.) &%dedent) / (&(%nl %dedent)) / (("" -> "Error while parsing Text") => error))
 inline_text_interpolation:
     "\" (
         variable / inline_list / inline_dict / inline_text
@@ -73,11 +73,11 @@ variable (Var): "%" { plain_word? }
 
 inline_list (List):
     !('[..]')
-    "[" %ws* {| (inline_list_item (comma inline_list_item)* comma?)? |} %ws* "]"
+    "[" %ws* ({| (inline_list_item (comma inline_list_item)* comma?)? |} -> Tuple) %ws* "]"
 indented_list (List):
-    "[..]" indent {|
+    "[..]" indent ({|
         list_line (nodent list_line)*
-    |}
+    |} -> Tuple)
     (dedent / (("" -> "Error while parsing list") => error))
 list_line:
      ((functioncall / expression) !comma)
@@ -86,17 +86,17 @@ inline_list_item: inline_functioncall / inline_expression
 
 inline_dict (Dict):
     !('{..}')
-    "{" %ws* {| (inline_dict_item (comma inline_dict_item)* comma?)? |} %ws* "}"
+    "{" %ws* ({| (inline_dict_item (comma inline_dict_item)* comma?)? |} -> Tuple) %ws* "}"
 indented_dict (Dict):
-    "{..}" indent {|
+    "{..}" indent ({|
         dict_line (nodent dict_line)*
-    |}
+    |} -> Tuple)
     (dedent / (("" -> "Error while parsing dict") => error))
 dict_line:
-    ({| {:dict_key: inline_expression / word :} %ws* ":" %ws* {:dict_value: functioncall / expression :} |} !comma)
+    (((inline_expression / word) %ws* ":" %ws* (functioncall / expression)) -> DictEntry !comma)
     / (inline_dict_item (comma dict_line?)?)
 inline_dict_item:
-    {| {:dict_key: inline_expression / word :} %ws* ":" %ws* {:dict_value: inline_functioncall / inline_expression :} |}
+    ((inline_expression / word) %ws* ":" %ws* (inline_functioncall / inline_expression)) -> DictEntry
 
 block_comment(Comment): "#.." { [^%nl]* (%nl+ %indent [^%nl]* (%nl+ %nodent [^%nl]*)* %dedent)? }
 line_comment(Comment): "#" { [^%nl]* }