diff --git a/code_obj.lua b/code_obj.lua
index 577eaf3..a8d7adf 100644
--- a/code_obj.lua
+++ b/code_obj.lua
@@ -78,7 +78,7 @@ do
   local _class_0
   local _base_0 = {
     is_code = true,
-    __tostring = function(self)
+    as_smext = function(self)
       if self.__str == nil then
         local buff, indent = { }, 0
         local match, gsub, rep
@@ -95,7 +95,7 @@ do
               end
             end
           else
-            b = tostring(b)
+            b = b:as_smext()
             if indent > 0 then
               b = gsub(b, "\n", "\n" .. rep(" ", indent))
             end
@@ -106,6 +106,9 @@ do
       end
       return self.__str
     end,
+    __tostring = function(self)
+      return self:as_smext()
+    end,
     as_lua = function(self)
       return tostring(self.__class.__name) .. "(" .. tostring(concat({
         tostring(self.source):as_lua(),
@@ -123,13 +126,13 @@ do
       }, ", ")) .. ")"
     end,
     __len = function(self)
-      return #tostring(self)
+      return #self:as_smext()
     end,
     match = function(self, ...)
-      return tostring(self):match(...)
+      return self:as_smext():match(...)
     end,
     gmatch = function(self, ...)
-      return tostring(self):gmatch(...)
+      return self:as_smext():gmatch(...)
     end,
     dirty = function(self)
       self.__str = nil
@@ -155,9 +158,6 @@ do
           if b.is_code then
             b.dirty = error
           end
-          if type(b) ~= 'string' and not (type(b) == 'table' and b.is_code) then
-            b = b:as_lua()
-          end
           bits[#bits + 1] = b
           _continue_0 = true
         until true
@@ -169,7 +169,7 @@ do
     end,
     trailing_line_len = function(self)
       if self._trailing_line_len == nil then
-        self._trailing_line_len = #tostring(self):match("[^\n]*$")
+        self._trailing_line_len = #self:as_smext():match("[^\n]*$")
       end
       return self._trailing_line_len
     end,
@@ -212,7 +212,9 @@ do
         if b.is_code then
           b.dirty = error
         end
-        b = tostring(b)
+        if not (type(b) == 'string') then
+          b = b:as_smext()
+        end
         local line = match(b, "\n([^\n]*)$")
         if line then
           line_len = #line
@@ -233,9 +235,6 @@ do
         if b.is_code then
           b.dirty = error
         end
-        if type(b) ~= 'string' and not (type(b) == 'table' and b.is_code) then
-          b = b:as_lua()
-        end
         bits[i] = b
       end
       return self:dirty()
@@ -253,7 +252,6 @@ do
       if type(self.source) == 'string' then
         self.source = Source:from_string(self.source)
       end
-      assert(self.source and Source:is_instance(self.source), "Source has the wrong type")
       return self:append(...)
     end,
     __base = _base_0,
@@ -402,8 +400,9 @@ do
             end
           else
             walk(b, pos)
+            b = b:as_smext()
           end
-          pos = pos + #tostring(b)
+          pos = pos + #b
         end
       end
       walk(self, 1)
diff --git a/containers.lua b/containers.lua
index ab632c4..b51b133 100644
--- a/containers.lua
+++ b/containers.lua
@@ -216,6 +216,8 @@ local _list_mt = {
     return rawset(self, k, v)
   end
 }
+_list_mt.__index.as_lua = _list_mt.as_lua
+_list_mt.__index.as_nomsu = _list_mt.as_nomsu
 List = function(t)
   return setmetatable(t, _list_mt)
 end
diff --git a/syntax_tree.lua b/syntax_tree.lua
index afdb631..851711a 100644
--- a/syntax_tree.lua
+++ b/syntax_tree.lua
@@ -11,7 +11,7 @@ AST.is_syntax_tree = function(n, t)
   if t == nil then
     t = nil
   end
-  return type(n) == 'table' and getmetatable(n) and AST[n.type] == getmetatable(n) and (t == nil or n.type == t)
+  return type(n) == 'table' and getmetatable(n) and getmetatable(n).__type == "Syntax Tree" and (t == nil or n.type == t)
 end
 local as_lua
 as_lua = function(self)
@@ -54,6 +54,7 @@ for _index_0 = 1, #types do
     cls.__index = cls
     cls.__name = name
     cls.type = name
+    cls.__type = "Syntax Tree"
     cls.is_instance = function(self, x)
       return getmetatable(x) == self
     end