concat is done outside of compiled func

etlua.lua

@@ -175,7 +175,13 @@ do
         return nil, err
       end
       return function(...)
-        return self:run(fn, ...)
+        local buffer
+        buffer, err = self:run(fn, ...)
+        if buffer then
+          return concat(buffer)
+        else
+          return nil, err
+        end
       end
     end,
     parse = function(self, str)
@@ -293,7 +299,7 @@ do
           error("unknown type " .. tostring(t))
         end
       end
-      push("return _concat(_b)")
+      push("return _b")
       return concat(buffer, "\n")
     end
   }
@@ -321,10 +327,10 @@ local compile = (function()
   end
 end)()
 local render
-render = function(str, env)
+render = function(str, ...)
   local fn, err = compile(str)
   if fn then
-    return fn(env)
+    return fn(...)
   else
     return nil, err
   end

etlua.moon

@@ -134,7 +134,12 @@ class Parser
     return nil, err unless success
     fn, err = @load @chunks_to_lua!
     return nil, err unless fn
-    (...) -> @run fn, ...
+    (...) ->
+      buffer, err = @run fn, ...
+      if buffer
+        concat buffer
+      else
+        nil, err
 
   parse: (@str) =>
     assert type(@str) == "string", "expecting string for parse"
@@ -228,7 +233,7 @@ class Parser
         else
           error "unknown type #{t}"
 
-    push "return _concat(_b)"
+    push "return _b"
     concat buffer, "\n"
 
 compile = Parser!\compile