diff --git a/bin/moon b/bin/moon
index e5b3119..5665a80 100755
--- a/bin/moon
+++ b/bin/moon
@@ -17,7 +17,7 @@ local help = [=[Usage: %s [options] [script [args]]
 ]=]
 
 local function print_err(...)
-	msg = table.concat({...}, "\t")
+	local msg = table.concat({...}, "\t")
 	io.stderr:write(msg .. "\n")
 end
 
@@ -49,7 +49,7 @@ local new_arg = {
 
 local moonscript_chunk, lua_parse_error
 local passed, err = pcall(function()
-	moonscript_chunk, lua_parse_error = moonscript.loadfile(script_fname)
+	moonscript_chunk, lua_parse_error = moonscript.loadfile(script_fname, { implicitly_return_root = false })
 end)
 
 if not passed then
@@ -70,16 +70,25 @@ getfenv(moonscript_chunk).arg = new_arg
 
 if not opts.d then
 	local err, trace
+
 	xpcall(function() moonscript_chunk(unpack(new_arg)) end, function(_err)
 		err = _err
 		trace = debug.traceback("", 2)
 	end)
 
 	if err then
-		local traceback = util.trim(trace)
-		traceback = moonscript.errors.truncate_traceback(traceback)
-		print_err(moonscript.errors.rewrite_traceback(traceback, err))
-		os.exit(1)
+		local truncated = moonscript.errors.truncate_traceback(util.trim(trace))
+		local rewritten = moonscript.errors.rewrite_traceback(truncated, err)
+
+		if rewritten then
+			print_err(rewritten)
+		else
+			-- faield to rewrite, show original
+			print_err(table.concat({
+				err,
+				util.trim(trace)
+			}, "\n"))
+		end
 	end
 else
 	moonscript_chunk(unpack(new_arg))
diff --git a/moonscript/compile.lua b/moonscript/compile.lua
index 6891c3c..35a1321 100644
--- a/moonscript/compile.lua
+++ b/moonscript/compile.lua
@@ -587,7 +587,9 @@ RootBlock = (function()
       return "RootBlock<>"
     end,
     root_stms = function(self, stms)
-      stms = transform.Statement.transformers.root_stms(self, stms)
+      if not (self.options.implicitly_return_root == false) then
+        stms = transform.Statement.transformers.root_stms(self, stms)
+      end
       local _list_0 = stms
       for _index_0 = 1, #_list_0 do
         local s = _list_0[_index_0]
@@ -607,9 +609,10 @@ RootBlock = (function()
     setmetatable(_base_0, _parent_0.__base)
   end
   local _class_0 = setmetatable({
-    __init = function(self, ...)
+    __init = function(self, options)
+      self.options = options
       self.root = self
-      return _parent_0.__init(self, ...)
+      return _parent_0.__init(self)
     end,
     __base = _base_0,
     __name = "RootBlock",
@@ -654,11 +657,12 @@ value = function(value)
   end
   return out
 end
-tree = function(tree, scope)
-  if scope == nil then
-    scope = RootBlock()
+tree = function(tree, options)
+  if options == nil then
+    options = { }
   end
   assert(tree, "missing tree")
+  local scope = (options.scope or RootBlock)(options)
   local runner = coroutine.create(function()
     return scope:root_stms(tree)
   end)
diff --git a/moonscript/compile.moon b/moonscript/compile.moon
index c1aae94..411ee9f 100644
--- a/moonscript/compile.moon
+++ b/moonscript/compile.moon
@@ -340,14 +340,15 @@ class Block
     @stms fn lines
 
 class RootBlock extends Block
-  new: (...) =>
+  new: (@options) =>
     @root = self
-    super ...
+    super!
 
   __tostring: => "RootBlock<>"
 
   root_stms: (stms) =>
-    stms = transform.Statement.transformers.root_stms self, stms
+    unless @options.implicitly_return_root == false
+      stms = transform.Statement.transformers.root_stms self, stms
     @stm s for s in *stms
 
   render: =>
@@ -372,9 +373,11 @@ value = (value) ->
     out = \render!
   out
 
-tree = (tree, scope=RootBlock!) ->
+tree = (tree, options={}) ->
   assert tree, "missing tree"
 
+  scope = (options.scope or RootBlock) options
+
   runner = coroutine.create ->
     scope\root_stms tree
 
diff --git a/moonscript/errors.lua b/moonscript/errors.lua
index 08c65e2..d895e50 100644
--- a/moonscript/errors.lua
+++ b/moonscript/errors.lua
@@ -85,11 +85,14 @@ rewrite_traceback = function(text, err)
   end
   err = rewrite_single(err)
   local match = g:match(text)
+  if not (match) then
+    return nil
+  end
   for i, trace in ipairs(match) do
     match[i] = rewrite_single(trace)
   end
   return concat({
-    "moon:" .. err,
+    "moon: " .. err,
     header_text,
     "\t" .. concat(match, "\n\t")
   }, "\n")
diff --git a/moonscript/errors.moon b/moonscript/errors.moon
index 4b48021..ede5fce 100644
--- a/moonscript/errors.moon
+++ b/moonscript/errors.moon
@@ -71,11 +71,14 @@ rewrite_traceback = (text, err) ->
 
   err = rewrite_single err
   match = g\match text
+
+  return nil unless match
+
   for i, trace in ipairs match
     match[i] = rewrite_single trace
 
   concat {
-    "moon:" .. err
+    "moon: " .. err
     header_text
     "\t" .. concat match, "\n\t"
   }, "\n"
diff --git a/moonscript/init.lua b/moonscript/init.lua
index 51a1e04..e895224 100644
--- a/moonscript/init.lua
+++ b/moonscript/init.lua
@@ -20,7 +20,10 @@ create_moonpath = function(package_path)
   end
   return concat(paths, ";")
 end
-to_lua = function(text)
+to_lua = function(text, options)
+  if options == nil then
+    options = { }
+  end
   if "string" ~= type(text) then
     local t = type(text)
     error("expecting string (got " .. t .. ")", 2)
@@ -29,7 +32,7 @@ to_lua = function(text)
   if not tree then
     error(err, 2)
   end
-  local code, ltable, pos = compile.tree(tree)
+  local code, ltable, pos = compile.tree(tree, options)
   if not code then
     error(compile.format_error(ltable, pos, text), 2)
   end
@@ -65,9 +68,12 @@ end
 if not _G.moon_no_loader then
   init_loader()
 end
-loadstring = function(str, chunk_name)
+loadstring = function(str, chunk_name, options)
+  if options == nil then
+    options = nil
+  end
   local passed, code, ltable = pcall(function()
-    return to_lua(str)
+    return to_lua(str, options)
   end)
   if not passed then
     error(chunk_name .. ": " .. code, 2)
@@ -77,16 +83,19 @@ loadstring = function(str, chunk_name)
   end
   return lua.loadstring(code, chunk_name or "=(moonscript.loadstring)")
 end
-loadfile = function(fname)
+loadfile = function(fname, options)
+  if options == nil then
+    options = nil
+  end
   local file, err = io.open(fname)
   if not file then
     return nil, err
   end
   local text = assert(file:read("*a"))
   file:close()
-  return loadstring(text, fname)
+  return loadstring(text, fname, options)
 end
-dofile = function(fname)
+dofile = function(fname, options)
   local f = assert(loadfile(fname))
   return f()
 end
diff --git a/moonscript/init.moon b/moonscript/init.moon
index b059387..61f15f8 100644
--- a/moonscript/init.moon
+++ b/moonscript/init.moon
@@ -24,7 +24,7 @@ create_moonpath = (package_path) ->
     if p then paths[i] = p..".moon"
   concat paths, ";"
 
-to_lua = (text) ->
+to_lua = (text, options={}) ->
   if "string" != type text
     t = type text
     error "expecting string (got ".. t ..")", 2
@@ -33,7 +33,7 @@ to_lua = (text) ->
   if not tree
     error err, 2
 
-  code, ltable, pos = compile.tree tree
+  code, ltable, pos = compile.tree tree, options
   if not code
     error compile.format_error(ltable, pos, text), 2
 
@@ -63,23 +63,23 @@ init_loader = ->
 
 init_loader! if not _G.moon_no_loader
 
-loadstring = (str, chunk_name) ->
-  passed, code, ltable = pcall -> to_lua str
+loadstring = (str, chunk_name, options=nil) ->
+  passed, code, ltable = pcall -> to_lua str, options
   if not passed
     error chunk_name .. ": " .. code, 2
 
   line_tables[chunk_name] = ltable if chunk_name
   lua.loadstring code, chunk_name or "=(moonscript.loadstring)"
 
-loadfile = (fname) ->
+loadfile = (fname, options=nil) ->
   file, err = io.open fname
   return nil, err if not file
   text = assert file\read "*a"
   file\close!
-  loadstring text, fname
+  loadstring text, fname, options
 
 -- throws errros
-dofile = (fname) ->
+dofile = (fname, options) ->
   f = assert loadfile fname
   f!