diff --git a/userspace/digwatch/digwatch.cpp b/userspace/digwatch/digwatch.cpp
index ecfe810d..fd0c47d9 100644
--- a/userspace/digwatch/digwatch.cpp
+++ b/userspace/digwatch/digwatch.cpp
@@ -45,18 +45,19 @@ static void usage()
     );
 }
 
+string lua_on_event = "on_event";
 
 //
 // Event processing loop
 //
 void do_inspect(sinsp* inspector,
 		digwatch_rules* rules,
-		digwatch_formats* formats)
+		digwatch_formats* formats,
+		lua_State* ls)
 {
 	int32_t res;
 	sinsp_evt* ev;
 	string line;
-	sinsp_evt_formatter* formatter;
 
 	//
 	// Loop through the events
@@ -89,20 +90,24 @@ void do_inspect(sinsp* inspector,
 			continue;
 		}
 
-		formatter = formats->lookup_formatter(ev->get_check_id());
-		if(!formatter)
+		lua_getglobal(ls, lua_on_event.c_str());
+
+		if(lua_isfunction(ls, -1))
 		{
-			throw sinsp_exception("Error: No formatter for event with id %d " + to_string(ev->get_check_id()));
+			lua_pushlightuserdata(ls, ev);
+			lua_pushnumber(ls, ev->get_check_id());
+
+			if(lua_pcall(ls, 2, 0, 0) != 0)
+			{
+				const char* lerr = lua_tostring(ls, -1);
+				string err = "Error installing rules: " + string(lerr);
+				throw sinsp_exception(err);
+			}
 		}
-
-		bool has_all = formatter->tostring(ev, &line);
-		if(!has_all) {
-			cout << "(missing fields) ";
+		else
+		{
+			throw sinsp_exception("No function " + lua_on_event + " found in lua compiler module");
 		}
-		cout << line;
-		cout << endl;
-
-
 	}
 }
 
@@ -111,7 +116,7 @@ void do_inspect(sinsp* inspector,
 //
 int digwatch_init(int argc, char **argv)
 {
-	int result;
+	int result = EXIT_SUCCESS;
 	sinsp* inspector = NULL;
 	digwatch_rules* rules = NULL;
 	digwatch_formats* formats = NULL;
@@ -120,7 +125,7 @@ int digwatch_init(int argc, char **argv)
 	int long_index = 0;
 	string lua_main_filename;
 	string lua_dir = DIGWATCH_INSTALLATION_DIR;
-	lua_State* ls;
+	lua_State* ls = NULL;
 
 	static struct option long_options[] =
 	{
@@ -147,7 +152,6 @@ int digwatch_init(int argc, char **argv)
 			{
 			case 'h':
 				usage();
-				result = EXIT_SUCCESS;
 				goto exit;
 			case 'm':
 				lua_main_filename = optarg;
@@ -220,7 +224,8 @@ int digwatch_init(int argc, char **argv)
 
 		do_inspect(inspector,
 			   rules,
-			   formats);
+			   formats,
+			   ls);
 
 		inspector->close();
 	}
@@ -242,7 +247,10 @@ exit:
 		delete inspector;
 	}
 
-	lua_close(ls);
+	if(ls)
+	{
+		lua_close(ls);
+	}
 	return result;
 }
 
diff --git a/userspace/digwatch/formats.cpp b/userspace/digwatch/formats.cpp
index 531c54e5..2c7d0f83 100644
--- a/userspace/digwatch/formats.cpp
+++ b/userspace/digwatch/formats.cpp
@@ -6,12 +6,12 @@ extern "C" {
 #include "lauxlib.h"
 }
 
-std::map<uint32_t, sinsp_evt_formatter*> g_format_map;
 sinsp* g_inspector;
 
 const static struct luaL_reg ll_digwatch [] =
 {
-	{"set_formatter", &digwatch_formats::set_formatter},
+	{"formatter", &digwatch_formats::formatter},
+	{"format_event", &digwatch_formats::format_event},
 	{NULL,NULL}
 };
 
@@ -24,20 +24,13 @@ digwatch_formats::digwatch_formats(sinsp* inspector, lua_State *ls)
 	luaL_openlib(m_ls, "digwatch", ll_digwatch, 0);
 }
 
-int digwatch_formats::set_formatter (lua_State *ls) {
-	uint32_t index = luaL_checkinteger(ls, 1);
-	string format = luaL_checkstring(ls, 2);
-
+int digwatch_formats::formatter(lua_State *ls)
+{
+	string format = luaL_checkstring(ls, 1);
+	sinsp_evt_formatter* formatter;
 	try
 	{
-		if(format == "" || format == "default")
-		{
-			g_format_map[index] = new sinsp_evt_formatter(g_inspector, DEFAULT_OUTPUT_STR);
-		}
-		else
-		{
-			g_format_map[index] = new sinsp_evt_formatter(g_inspector, format);
-		}
+		formatter = new sinsp_evt_formatter(g_inspector, format);
 	}
 	catch(sinsp_exception& e)
 	{
@@ -46,12 +39,25 @@ int digwatch_formats::set_formatter (lua_State *ls) {
 		throw sinsp_exception("set_formatter error");
 	}
 
-	return 0;
+	lua_pushlightuserdata(ls, formatter);
+
+	return 1;
 }
 
-sinsp_evt_formatter* digwatch_formats::lookup_formatter(uint32_t index)
+int digwatch_formats::format_event (lua_State *ls)
 {
-	return g_format_map[index];
+	string line;
+
+	if (!lua_islightuserdata(ls, -1) || !lua_islightuserdata(ls, -2)) {
+		string err = "invalid arguments passed to format_event() ";
+		throw sinsp_exception("format_event error");
+	}
+	sinsp_evt* evt = (sinsp_evt*)lua_topointer(ls, 1);
+	sinsp_evt_formatter* formatter = (sinsp_evt_formatter*)lua_topointer(ls, 2);
+
+	formatter->tostring(evt, &line);
+
+	lua_pushstring(ls, line.c_str());
+	return 1;
 }
 
-
diff --git a/userspace/digwatch/formats.h b/userspace/digwatch/formats.h
index 7cb84c61..913c461c 100644
--- a/userspace/digwatch/formats.h
+++ b/userspace/digwatch/formats.h
@@ -10,9 +10,11 @@ class digwatch_formats
  public:
 	digwatch_formats(sinsp* inspector, lua_State *ls);
 
-	// set_formatter(index, format_string)
-	static int set_formatter(lua_State *ls);
-	sinsp_evt_formatter* lookup_formatter(uint32_t index);
+	// formatter = digwatch.formatter(format_string)
+	static int formatter(lua_State *ls);
+
+	// formatted_string = digwatch.format_event(evt, formatter)
+	static int format_event(lua_State *ls);
 
  private:
 	lua_State* m_ls;
diff --git a/userspace/digwatch/lua/compiler.lua b/userspace/digwatch/lua/compiler.lua
index aadd33bc..0bda6965 100644
--- a/userspace/digwatch/lua/compiler.lua
+++ b/userspace/digwatch/lua/compiler.lua
@@ -167,13 +167,13 @@ local function outputformat (format)
    return {type = "OutputFormat", value = format}
 end
 
-local function functioncall (name, args)
-   return {type = "FunctionCall", name = name, arguments = args}
+local function functioncall (str, mname, fname, args)
+   return {type = "FunctionCall", mname = mname, fname = fname, arguments = args, source = str}
 end
 
 local function rule(filter, output)
    if not output then
-      output = outputformat("")
+      output = outputformat(nil)
    end
    return {type = "Rule", filter = filter, output = output}
 end
@@ -217,7 +217,7 @@ local G = {
   MacroDef = (C(V"Macro") * V"Skip" * V"Colon" * (V"Filter"));
 
   FuncArgs = symb("(") * list(V"Value", symb(",")) * symb(")");
-  Output = ((V"Name" * V"FuncArgs") / functioncall) + P(1)^0 / outputformat;
+  Output = (C(V"Name" * P(".") * V"Name" * V"FuncArgs") / functioncall) + P(1)^0 / outputformat;
 
   -- Terminals
   Value = terminal "Number" + terminal "String" + terminal "BareString";
@@ -462,7 +462,7 @@ function print_ast(ast, level)
       print(ast.value)
 
    elseif t == "FunctionCall" then
-      print(ast.name .. "(" )
+      print(ast.mname..ast.fname .. "(" )
       print_ast(ast.arguments)
       print(")")
 
diff --git a/userspace/digwatch/lua/rule_loader.lua b/userspace/digwatch/lua/rule_loader.lua
index a7963d9f..bd913280 100644
--- a/userspace/digwatch/lua/rule_loader.lua
+++ b/userspace/digwatch/lua/rule_loader.lua
@@ -5,6 +5,8 @@
 
 --]]
 
+local DEFAULT_OUTPUT_FORMAT = "%evt.num %evt.time %evt.cpu %proc.name (%thread.tid) %evt.dir %evt.type %evt.args"
+
 local compiler = require "compiler"
 
 --[[
@@ -72,10 +74,31 @@ local state
    to the line-oriented compiler.
 --]]
 local function init()
-   return {macros={}, filter_ast=nil, n_rules=0}
+   return {macros={}, filter_ast=nil, n_rules=0, outputs={}}
 end
 
 
+function set_output(output_ast)
+
+   if(output_ast.type == "OutputFormat") then
+
+      local format
+      if output_ast.value==nil then
+	 format = DEFAULT_OUTPUT_FORMAT
+      else
+	 format = output_ast.value
+      end
+
+      state.outputs[state.n_rules] = {type="format", formatter=digwatch.formatter(format)}
+
+   elseif (output_ast.type == "FunctionCall") then
+      require(output_ast.mname)
+      state.outputs[state.n_rules] = {type="function", mname = output_ast.mname, source=output_ast.source}
+   else
+      error ("Unexpected type in set_output: ".. output_ast.type)
+   end
+end
+
 function load_rule(r)
    if (state == nil) then
       state = init()
@@ -90,8 +113,9 @@ function load_rule(r)
       error ("Unexpected type in load_rule: "..line_ast.type)
    end
 
-   -- Register a formatter with the output string from this rule
-   digwatch.set_formatter(state.n_rules, line_ast.output.value)
+   state.n_rules = state.n_rules + 1
+
+   set_output(line_ast.output)
 
    -- Store the index of this formatter in each relational expression that
    -- this rule contains.
@@ -100,8 +124,6 @@ function load_rule(r)
    -- event.
    mark_relational_nodes(line_ast.filter.value, state.n_rules)
 
-   state.n_rules = state.n_rules + 1
-
    -- Rule ASTs are merged together into one big AST, with "OR" between each
    -- rule.
    if (state.filter_ast == nil) then
@@ -114,3 +136,15 @@ end
 function on_done()
    install_filter(state.filter_ast)
 end
+
+evt = nil
+function on_event(evt_, rule_id)
+   if state.outputs[rule_id].type == "format" then
+      print(digwatch.format_event(evt, state.outputs[rule_id].formatter))
+   elseif state.outputs[rule_id].type == "function" then
+      local reqmod =  "local "..state.outputs[rule_id].mname.." = require('" ..state.outputs[rule_id].mname .. "')";
+      evt = evt_
+      assert(loadstring(reqmod .. "; print(type(evt));" ..state.outputs[rule_id].source))()
+   end
+end
+