diff --git a/nomsu.lua b/nomsu.lua
index 4d80357..ca007e6 100644
--- a/nomsu.lua
+++ b/nomsu.lua
@@ -235,7 +235,12 @@ setmetatable(NOMSU_DEFS, {
   __index = function(self, key)
     local make_node
     make_node = function(src, ...)
-      return Types[key](...)
+      local tree = Types[key](...)
+      insert(lpeg.userdata.depth_first_sources, {
+        src,
+        tree
+      })
+      return tree
     end
     self[key] = make_node
     return make_node
@@ -316,7 +321,8 @@ do
         indent_stack = {
           ""
         },
-        errors = { }
+        errors = { },
+        depth_first_sources = { }
       }
       local old_userdata
       old_userdata, lpeg.userdata = lpeg.userdata, userdata
@@ -339,7 +345,25 @@ do
         end
         error(concat(errors, "\n\n"), 0)
       end
-      return tree
+      local src_map = { }
+      local src_i = 1
+      local walk_tree
+      walk_tree = function(tree, path)
+        if tree.is_multi then
+          for i, v in ipairs(tree) do
+            if Types.is_node(v) then
+              walk_tree(v, Tuple(i, path))
+            end
+          end
+        end
+        local src, t2 = unpack(userdata.depth_first_sources[src_i])
+        src_i = src_i + 1
+        assert(t2 == tree)
+        src_map[path] = src
+      end
+      walk_tree(tree, Tuple())
+      assert(src_i == #userdata.depth_first_sources + 1)
+      return tree, src_map
     end,
     run = function(self, nomsu_code, compile_fn)
       if compile_fn == nil then
@@ -441,7 +465,10 @@ do
       end
       return run_lua_fn()
     end,
-    tree_to_lua = function(self, tree)
+    tree_to_lua = function(self, tree, path)
+      if path == nil then
+        path = Tuple()
+      end
       local _exp_0 = tree.type
       if "Action" == _exp_0 then
         local stub = tree:get_stub()
@@ -484,7 +511,7 @@ do
             if tok.type == "Word" then
               lua:append(tok.value)
             else
-              local tok_lua = self:tree_to_lua(tok)
+              local tok_lua = self:tree_to_lua(tok, Tuple(i, path))
               if not (tok_lua.is_value) then
                 error("non-expression value inside math expression: " .. tostring(colored.yellow(repr(tok))))
               end
@@ -507,7 +534,7 @@ do
               _continue_0 = true
               break
             end
-            local arg_lua = self:tree_to_lua(tok)
+            local arg_lua = self:tree_to_lua(tok, Tuple(i, path))
             if not (arg_lua.is_value) then
               error("Cannot use:\n" .. tostring(colored.yellow(repr(tok))) .. "\nas an argument to " .. tostring(stub) .. ", since it's not an expression, it produces: " .. tostring(repr(arg_lua)), 0)
             end
@@ -560,14 +587,14 @@ do
             end
             return t.type .. "(" .. table.concat(bits, ", ") .. ")"
           else
-            return t.type .. "(" .. make_tree(t.value) .. ")"
+            return t.type .. "(" .. make_tree(t[1]) .. ")"
           end
         end
-        return Lua.Value(nil, make_tree(tree.value))
+        return Lua.Value(nil, make_tree(tree[1]))
       elseif "Block" == _exp_0 then
         local lua = Lua()
         for i, line in ipairs(tree) do
-          local line_lua = self:tree_to_lua(line)
+          local line_lua = self:tree_to_lua(line, Tuple(i, path))
           if i > 1 then
             lua:append("\n")
           end
@@ -577,10 +604,9 @@ do
       elseif "Text" == _exp_0 then
         local lua = Lua.Value()
         local string_buffer = ""
-        for _index_0 = 1, #tree do
+        for i, bit in ipairs(tree) do
           local _continue_0 = false
           repeat
-            local bit = tree[_index_0]
             if type(bit) == "string" then
               string_buffer = string_buffer .. bit
               _continue_0 = true
@@ -593,7 +619,7 @@ do
               lua:append(repr(string_buffer))
               string_buffer = ""
             end
-            local bit_lua = self:tree_to_lua(bit)
+            local bit_lua = self:tree_to_lua(bit, Tuple(i, path))
             if not (bit_lua.is_value) then
               error("Cannot use " .. tostring(colored.yellow(repr(bit))) .. " as a string interpolation value, since it's not an expression.", 0)
             end
@@ -624,7 +650,7 @@ do
         local lua = Lua.Value(nil, "{")
         local line_length = 0
         for i, item in ipairs(tree) do
-          local item_lua = self:tree_to_lua(item)
+          local item_lua = self:tree_to_lua(item, Tuple(i, path))
           if not (item_lua.is_value) then
             error("Cannot use " .. tostring(colored.yellow(repr(item))) .. " as a list item, since it's not an expression.", 0)
           end
@@ -652,7 +678,7 @@ do
         local lua = Lua.Value(nil, "{")
         local line_length = 0
         for i, entry in ipairs(tree) do
-          local entry_lua = self:tree_to_lua(entry)
+          local entry_lua = self:tree_to_lua(entry, Tuple(i, path))
           lua:append(entry_lua)
           local entry_lua_str = tostring(entry_lua)
           local last_line = entry_lua_str:match("\n([^\n]*)$")
@@ -675,11 +701,11 @@ do
         return lua
       elseif "DictEntry" == _exp_0 then
         local key, value = tree[1], tree[2]
-        local key_lua = self:tree_to_lua(key)
+        local key_lua = self:tree_to_lua(key, Tuple(1, path))
         if not (key_lua.is_value) then
           error("Cannot use " .. tostring(colored.yellow(repr(key))) .. " as a dict key, since it's not an expression.", 0)
         end
-        local value_lua = value and self:tree_to_lua(value) or Lua.Value(nil, "true")
+        local value_lua = value and self:tree_to_lua(value, Tuple(2, path)) or Lua.Value(nil, "true")
         if not (value_lua.is_value) then
           error("Cannot use " .. tostring(colored.yellow(repr(value))) .. " as a dict value, since it's not an expression.", 0)
         end
@@ -692,7 +718,7 @@ do
           return Lua(nil, "[", key_lua, "]=", value_lua)
         end
       elseif "IndexChain" == _exp_0 then
-        local lua = self:tree_to_lua(tree[1])
+        local lua = self:tree_to_lua(tree[1], Tuple(1, path))
         if not (lua.is_value) then
           error("Cannot index " .. tostring(colored.yellow(repr(tree[1]))) .. ", since it's not an expression.", 0)
         end
@@ -702,7 +728,7 @@ do
         end
         for i = 2, #tree do
           local key = tree[i]
-          local key_lua = self:tree_to_lua(key)
+          local key_lua = self:tree_to_lua(key, Tuple(i, path))
           if not (key_lua.is_value) then
             error("Cannot use " .. tostring(colored.yellow(repr(key))) .. " as an index, since it's not an expression.", 0)
           end
@@ -822,7 +848,7 @@ do
       elseif "EscapedNomsu" == _exp_0 then
         local nomsu = self:tree_to_nomsu(tree.value, true)
         if nomsu == nil and not inline then
-          nomsu = self:tree_to_nomsu(tree.value)
+          nomsu = self:tree_to_nomsu(tree[1])
           return nomsu and Nomsu(nil, "\\:\n    ", nomsu)
         end
         return nomsu and Nomsu(nil, "\\(", nomsu, ")")
@@ -1070,16 +1096,13 @@ do
         depth = 0
       end
       coroutine.yield(tree, depth)
-      if not (Types.is_node(tree)) then
-        return 
-      end
       if tree.is_multi then
         for _index_0 = 1, #tree do
           local v = tree[_index_0]
-          self:walk_tree(v, depth + 1)
+          if Types.is_node(v) then
+            self:walk_tree(v, depth + 1)
+          end
         end
-      else
-        return self:walk_tree(v, depth + 1)
       end
     end,
     initialize_core = function(self)
diff --git a/nomsu.moon b/nomsu.moon
index d8ae4e0..7648998 100755
--- a/nomsu.moon
+++ b/nomsu.moon
@@ -201,7 +201,9 @@ NOMSU_DEFS = with {}
 
 setmetatable(NOMSU_DEFS, {__index:(key)=>
     make_node = (src, ...)->
-        Types[key](...)
+        tree = Types[key](...)
+        insert lpeg.userdata.depth_first_sources, {src, tree}
+        return tree
     self[key] = make_node
     return make_node
 })
@@ -327,6 +329,7 @@ class NomsuCompiler
             nomsu_code = Nomsu(filename, nomsu_code)
         userdata = {
             source_code:nomsu_code, indent_stack: {""}, errors: {},
+            depth_first_sources: {},
         }
 
         old_userdata, lpeg.userdata = lpeg.userdata, userdata
@@ -340,8 +343,22 @@ class NomsuCompiler
             table.sort(keys)
             errors = [userdata.errors[k] for k in *keys]
             error(concat(errors, "\n\n"), 0)
-            
-        return tree
+        
+        src_map = {}
+        src_i = 1
+        walk_tree = (tree, path)->
+            if tree.is_multi
+                for i, v in ipairs tree
+                    if Types.is_node(v)
+                        walk_tree(v, Tuple(i, path))
+            src, t2 = unpack(userdata.depth_first_sources[src_i])
+            src_i += 1
+            assert t2 == tree
+            src_map[path] = src
+        walk_tree tree, Tuple!
+        assert src_i == #userdata.depth_first_sources + 1
+
+        return tree, src_map
 
     run: (nomsu_code, compile_fn=nil)=>
         if #tostring(nomsu_code) == 0 then return nil
@@ -410,7 +427,7 @@ class NomsuCompiler
 
     MAX_LINE = 80 -- For beautification purposes, try not to make lines much longer than this value
     math_expression = re.compile [[ ([+-] " ")* "%" (" " [*/^+-] (" " [+-])* " %")+ !. ]]
-    tree_to_lua: (tree)=>
+    tree_to_lua: (tree, path=Tuple!)=>
         switch tree.type
             when "Action"
                 stub = tree\get_stub!
@@ -420,6 +437,7 @@ class NomsuCompiler
                     -- Force all compile-time actions to take a tree location
                     args = [args[p-1] for p in *@environment.ARG_ORDERS[compile_action][stub]]
                     -- Force Lua to avoid tail call optimization for debugging purposes
+                    -- TODO: use tail call
                     ret = compile_action(tree, unpack(args))
                     if not ret then error("Failed to produce any Lua")
                     return ret
@@ -433,7 +451,7 @@ class NomsuCompiler
                         if tok.type == "Word"
                             lua\append tok.value
                         else
-                            tok_lua = @tree_to_lua(tok)
+                            tok_lua = @tree_to_lua(tok, Tuple(i, path))
                             unless tok_lua.is_value
                                 error("non-expression value inside math expression: #{colored.yellow repr(tok)}")
                             if tok.type == "Action"
@@ -446,7 +464,7 @@ class NomsuCompiler
                 args = {}
                 for i, tok in ipairs tree
                     if tok.type == "Word" then continue
-                    arg_lua = @tree_to_lua(tok)
+                    arg_lua = @tree_to_lua(tok, Tuple(i, path))
                     unless arg_lua.is_value
                         error "Cannot use:\n#{colored.yellow repr(tok)}\nas an argument to #{stub}, since it's not an expression, it produces: #{repr arg_lua}", 0
                     insert args, arg_lua
@@ -471,13 +489,13 @@ class NomsuCompiler
                         bits = [make_tree(bit) for bit in *t]
                         return t.type.."("..table.concat(bits, ", ")..")"
                     else
-                        return t.type.."("..make_tree(t.value)..")"
-                Lua.Value nil, make_tree(tree.value)
+                        return t.type.."("..make_tree(t[1])..")"
+                Lua.Value nil, make_tree(tree[1])
             
             when "Block"
                 lua = Lua!
                 for i,line in ipairs tree
-                    line_lua = @tree_to_lua(line)
+                    line_lua = @tree_to_lua(line, Tuple(i, path))
                     if i > 1
                         lua\append "\n"
                     lua\append line_lua\as_statements!
@@ -486,7 +504,7 @@ class NomsuCompiler
             when "Text"
                 lua = Lua.Value!
                 string_buffer = ""
-                for bit in *tree
+                for i, bit in ipairs tree
                     if type(bit) == "string"
                         string_buffer ..= bit
                         continue
@@ -494,7 +512,7 @@ class NomsuCompiler
                         if #lua.bits > 0 then lua\append ".."
                         lua\append repr(string_buffer)
                         string_buffer = ""
-                    bit_lua = @tree_to_lua(bit)
+                    bit_lua = @tree_to_lua(bit, Tuple(i, path))
                     unless bit_lua.is_value
                         error "Cannot use #{colored.yellow repr(bit)} as a string interpolation value, since it's not an expression.", 0
                     if #lua.bits > 0 then lua\append ".."
@@ -514,7 +532,7 @@ class NomsuCompiler
                 lua = Lua.Value nil, "{"
                 line_length = 0
                 for i, item in ipairs tree
-                    item_lua = @tree_to_lua(item)
+                    item_lua = @tree_to_lua(item, Tuple(i, path))
                     unless item_lua.is_value
                         error "Cannot use #{colored.yellow repr(item)} as a list item, since it's not an expression.", 0
                     lua\append item_lua
@@ -538,7 +556,7 @@ class NomsuCompiler
                 lua = Lua.Value nil, "{"
                 line_length = 0
                 for i, entry in ipairs tree
-                    entry_lua = @tree_to_lua(entry)
+                    entry_lua = @tree_to_lua(entry, Tuple(i, path))
                     lua\append entry_lua
                     entry_lua_str = tostring(entry_lua)
                     -- TODO: maybe make this more accurate? It's only a heuristic, so eh...
@@ -559,10 +577,10 @@ class NomsuCompiler
 
             when "DictEntry"
                 key, value = tree[1], tree[2]
-                key_lua = @tree_to_lua(key)
+                key_lua = @tree_to_lua(key, Tuple(1, path))
                 unless key_lua.is_value
                     error "Cannot use #{colored.yellow repr(key)} as a dict key, since it's not an expression.", 0
-                value_lua = value and @tree_to_lua(value) or Lua.Value(nil, "true")
+                value_lua = value and @tree_to_lua(value, Tuple(2, path)) or Lua.Value(nil, "true")
                 unless value_lua.is_value
                     error "Cannot use #{colored.yellow repr(value)} as a dict value, since it's not an expression.", 0
                 key_str = tostring(key_lua)\match([=[["']([a-zA-Z_][a-zA-Z0-9_]*)['"]]=])
@@ -577,7 +595,7 @@ class NomsuCompiler
                     Lua nil, "[",key_lua,"]=",value_lua
             
             when "IndexChain"
-                lua = @tree_to_lua(tree[1])
+                lua = @tree_to_lua(tree[1], Tuple(1, path))
                 unless lua.is_value
                     error "Cannot index #{colored.yellow repr(tree[1])}, since it's not an expression.", 0
                 first_char = tostring(lua)\sub(1,1)
@@ -586,7 +604,7 @@ class NomsuCompiler
 
                 for i=2,#tree
                     key = tree[i]
-                    key_lua = @tree_to_lua(key)
+                    key_lua = @tree_to_lua(key, Tuple(i, path))
                     unless key_lua.is_value
                         error "Cannot use #{colored.yellow repr(key)} as an index, since it's not an expression.", 0
                     key_lua_str = tostring(key_lua)
@@ -684,7 +702,7 @@ class NomsuCompiler
             when "EscapedNomsu"
                 nomsu = @tree_to_nomsu(tree.value, true)
                 if nomsu == nil and not inline
-                    nomsu = @tree_to_nomsu(tree.value)
+                    nomsu = @tree_to_nomsu(tree[1])
                     return nomsu and Nomsu nil, "\\:\n    ", nomsu
                 return nomsu and Nomsu nil, "\\(", nomsu, ")"
 
@@ -866,12 +884,10 @@ class NomsuCompiler
 
     walk_tree: (tree, depth=0)=>
         coroutine.yield(tree, depth)
-        return unless Types.is_node(tree)
         if tree.is_multi
             for v in *tree
-                @walk_tree(v, depth+1)
-        else
-            @walk_tree(v, depth+1)
+                if Types.is_node(v)
+                    @walk_tree(v, depth+1)
 
     initialize_core: =>
         -- Sets up some core functionality
diff --git a/nomsu_tree.lua b/nomsu_tree.lua
index f4f10b2..4bacdb5 100644
--- a/nomsu_tree.lua
+++ b/nomsu_tree.lua
@@ -57,7 +57,7 @@ Tree = function(name, kind, methods)
           return _accum_0
         end)(), ', ')) .. ")"
       end
-      methods.map = function(self, fn)
+      methods._map = function(self, fn)
         do
           local ret = fn(self)
           if ret then
@@ -70,7 +70,7 @@ Tree = function(name, kind, methods)
           local _len_0 = 1
           for _index_0 = 1, #self do
             local v = self[_index_0]
-            _accum_0[_len_0] = v.map and v:map(fn) or v
+            _accum_0[_len_0] = v._map and v:_map(fn) or v
             _len_0 = _len_0 + 1
           end
           new_vals = _accum_0
@@ -82,7 +82,7 @@ Tree = function(name, kind, methods)
       methods.__tostring = function(self)
         return tostring(self.name) .. "(" .. tostring(repr(self.value)) .. ")"
       end
-      methods.map = function(self, fn)
+      methods._map = function(self, fn)
         return fn(self) or self
       end
     end
@@ -96,6 +96,7 @@ Tree = function(name, kind, methods)
   end
 end
 Tree("Block", 'multi')
+Tree("EscapedNomsu", 'multi')
 Tree("Text", 'multi')
 Tree("List", 'multi')
 Tree("Dict", 'multi')
@@ -104,11 +105,6 @@ Tree("IndexChain", 'multi')
 Tree("Number", 'single')
 Tree("Word", 'single')
 Tree("Comment", 'single')
-Tree("EscapedNomsu", 'single', {
-  map = function(self, fn)
-    return fn(self) or self:map(fn)
-  end
-})
 Tree("Var", 'single', {
   as_lua_id = function(self)
     return "_" .. (self.value:gsub("%W", function(c)
diff --git a/nomsu_tree.moon b/nomsu_tree.moon
index c15d29c..2f7c202 100644
--- a/nomsu_tree.moon
+++ b/nomsu_tree.moon
@@ -32,15 +32,15 @@ Tree = (name, kind, methods)->
             return @_map(fn)
         if is_multi
             .__tostring = => "#{@name}(#{table.concat [repr(v) for v in *@], ', '})"
-            .map = (fn)=>
+            ._map = (fn)=>
                 if ret = fn(@)
                     return ret
-                new_vals = [v.map and v\map(fn) or v for v in *@]
+                new_vals = [v._map and v\_map(fn) or v for v in *@]
                 ret = getmetatable(self)(unpack(new_vals))
                 return ret
         else
             .__tostring = => "#{@name}(#{repr(@value)})"
-            .map = (fn)=>
+            ._map = (fn)=>
                 fn(@) or @
 
     if is_multi
@@ -49,6 +49,7 @@ Tree = (name, kind, methods)->
         Types[name] = immutable {"value"}, methods
 
 Tree "Block", 'multi'
+Tree "EscapedNomsu", 'multi'
 Tree "Text", 'multi'
 Tree "List", 'multi'
 Tree "Dict", 'multi'
@@ -58,9 +59,6 @@ Tree "Number", 'single'
 Tree "Word", 'single'
 Tree "Comment", 'single'
 
-Tree "EscapedNomsu", 'single',
-    map: (fn)=> fn(@) or @\map(fn)
-
 Tree "Var", 'single',
     as_lua_id: =>
         "_"..(@value\gsub("%W", (c)-> if c == "_" then "__" else ("_%x")\format(c\byte!)))