diff --git a/README.md b/README.md
index 0904e76..1fe6577 100644
--- a/README.md
+++ b/README.md
@@ -225,10 +225,15 @@ the `register()` function to register your functions to the
 calculator. This function takes these parameters:
 
 - function name
-- number of arguments expected (1,2 or -1 allowed), -1 means batch
-  mode
+- number of arguments expected (see below)
 - help text
 
+Number of expected arguments can be:
+
+- 0: expect 1 argument but do NOT modify the stack
+- 1-n: do a singular calculation
+- -1: batch mode work with all numbers on the stack 
+
 Please [refer to the lua language
 reference](https://www.lua.org/manual/5.4/) for more details about
 LUA.
diff --git a/calc.go b/calc.go
index dedc461..d9d2275 100644
--- a/calc.go
+++ b/calc.go
@@ -151,16 +151,16 @@ func NewCalc() *Calc {
 	// pre-calculate mode switching arrays
 	c.Constants = strings.Split(Constants, " ")
 
-	for name := range LuaFuncs {
-		c.LuaFunctions = append(c.LuaFunctions, name)
-	}
-
 	return &c
 }
 
-// setup the interpreter, called from main()
+// setup the interpreter, called from main(), import lua functions
 func (c *Calc) SetInt(I *Interpreter) {
 	c.interpreter = I
+
+	for name := range LuaFuncs {
+		c.LuaFunctions = append(c.LuaFunctions, name)
+	}
 }
 
 func (c *Calc) ToggleDebug() {
@@ -448,6 +448,8 @@ func (c *Calc) luafunc(funcname string) {
 	var err error
 
 	switch c.interpreter.FuncNumArgs(funcname) {
+	case 0:
+		fallthrough
 	case 1:
 		x, err = c.interpreter.CallLuaFunc(funcname, c.stack.Last())
 	case 2:
@@ -465,7 +467,15 @@ func (c *Calc) luafunc(funcname string) {
 
 	c.stack.Backup()
 
+	dopush := true
+
 	switch c.interpreter.FuncNumArgs(funcname) {
+	case 0:
+		a := c.stack.Last()
+		if len(a) == 1 {
+			c.History("%s(%f) = %f", funcname, a, x)
+		}
+		dopush = false
 	case 1:
 		a := c.stack.Pop()
 		c.History("%s(%f) = %f", funcname, a, x)
@@ -478,7 +488,9 @@ func (c *Calc) luafunc(funcname string) {
 		c.History("%s(*) = %f", funcname, x)
 	}
 
-	c.stack.Push(x)
+	if dopush {
+		c.stack.Push(x)
+	}
 
 	c.Result()
 }
diff --git a/example.lua b/example.lua
new file mode 100644
index 0000000..fa38af7
--- /dev/null
+++ b/example.lua
@@ -0,0 +1,38 @@
+-- simple function, return the lower number of the two operands
+function lower(a,b)
+    if a < b then
+        return a
+    else
+        return b
+    end
+end
+
+-- calculate parallel resistance. Batch  function (registered with -1,
+-- see below). Takes a table as parameter.
+--
+-- Formula: 1/( (1/R1) + (1/R2) + ...)
+function parallelresistance(list)
+    sumres = 0
+    
+    for i, value in ipairs(list) do
+        sumres = sumres + 1 / value
+    end
+
+    return 1 / sumres
+end
+
+-- converter example
+function inch2centimeter(inches)
+    return inches * 2.54
+end
+
+function init()
+    -- expects 2 args
+    register("lower", 2, "lower")
+
+    -- expects a list of all numbers on the stack, batch mode
+    register("parallelresistance", -1, "parallel resistance")
+
+    -- expects 1 arg, but doesn't pop()
+    register("inch2centimeter", 0)
+end  
diff --git a/interpreter.go b/interpreter.go
index 39c0ed8..760a5af 100644
--- a/interpreter.go
+++ b/interpreter.go
@@ -25,7 +25,8 @@ import (
 )
 
 type Interpreter struct {
-	debug bool
+	debug  bool
+	script string
 }
 
 // LUA interpreter, instanciated in main()
@@ -42,8 +43,12 @@ type LuaFunction struct {
 // have access to the interpreter instance
 var LuaFuncs map[string]LuaFunction
 
+func NewInterpreter(script string, debug bool) *Interpreter {
+	return &Interpreter{debug: debug, script: script}
+}
+
 // initialize the lua environment properly
-func InitLua(config string, debug bool) *Interpreter {
+func (i *Interpreter) InitLua() {
 	// we only  load a subset of lua Open  modules and don't allow
 	// net, system or io stuff
 	for _, pair := range []struct {
@@ -66,7 +71,7 @@ func InitLua(config string, debug bool) *Interpreter {
 	}
 
 	// load the lua config (which we expect to contain init() and math functions)
-	if err := L.DoFile(config); err != nil {
+	if err := L.DoFile(i.script); err != nil {
 		panic(err)
 	}
 
@@ -84,8 +89,6 @@ func InitLua(config string, debug bool) *Interpreter {
 	}); err != nil {
 		panic(err)
 	}
-
-	return &Interpreter{debug: debug}
 }
 
 func (i *Interpreter) Debug(msg string) {
@@ -113,6 +116,8 @@ func (i *Interpreter) CallLuaFunc(funcname string, items []float64) (float64, er
 		funcname, LuaFuncs[funcname].numargs))
 
 	switch LuaFuncs[funcname].numargs {
+	case 0:
+		fallthrough
 	case 1:
 		// 1 arg variant
 		if err := L.CallByParam(lua.P{
diff --git a/main.go b/main.go
index 9df9488..d9ad1c8 100644
--- a/main.go
+++ b/main.go
@@ -30,7 +30,7 @@ import (
 	lua "github.com/yuin/gopher-lua"
 )
 
-const VERSION string = "2.0.5"
+const VERSION string = "2.0.6"
 
 const Usage string = `This is rpn, a reverse polish notation calculator cli.
 
@@ -98,8 +98,9 @@ func main() {
 	// our config file is interpreted  as lua code, only functions can
 	// be defined, init() will be called by InitLua().
 	if _, err := os.Stat(configfile); err == nil {
-		I := InitLua(configfile, enabledebug)
-		calc.SetInt(I)
+		luarunner := NewInterpreter(configfile, enabledebug)
+		luarunner.InitLua()
+		calc.SetInt(luarunner)
 	}
 
 	if len(flag.Args()) > 1 {
diff --git a/rpn.go b/rpn.go
index 4b6bee6..2496d37 100644
--- a/rpn.go
+++ b/rpn.go
@@ -210,7 +210,6 @@ COMMENTS
 
     In this case only 123 will be added to the stack.
 
-
 VARIABLES
     You can register the last item of the stack into a variable. Variable
     names must be all caps. Use the ">NAME" command to put a value into
@@ -245,8 +244,13 @@ EXTENDING RPN USING LUA
 
     *   function name
 
-    *   number of arguments expected (1,2 or -1 allowed), -1 means batch
-        mode.
+    *   number of arguments expected (see below)
+
+        Number of expected arguments can be:
+
+            - 0: expect 1 argument but do NOT modify the stack
+            - 1-n: do a singular calculation
+            - -1: batch mode work with all numbers on the stack
 
     *   help text
 
diff --git a/rpn.pod b/rpn.pod
index 7fce755..899f181 100644
--- a/rpn.pod
+++ b/rpn.pod
@@ -273,8 +273,13 @@ function name
 
 =item *
 
-number of arguments expected (1,2 or -1 allowed), -1 means batch
-mode.
+number of arguments expected (see below)
+
+Number of expected arguments can be:
+
+    - 0: expect 1 argument but do NOT modify the stack
+    - 1-n: do a singular calculation
+    - -1: batch mode work with all numbers on the stack 
 
 =item *
 
diff --git a/test.lua b/test.lua
deleted file mode 100644
index f71649e..0000000
--- a/test.lua
+++ /dev/null
@@ -1,17 +0,0 @@
-function add(a,b)
-  return a + b
-end
-
-function test(a)
-  return a
-end  
-
-function parallelresistance(a,b)
-  return 1.0 / (a * b)
-end
-
-function init()
-  register("add", 2, "addition")
-  register("test", 1, "test")
-  register("parallelresistance", 2, "parallel resistance")
-end