diff --git a/lib/exec.c b/lib/exec.c
index 7deae29..70ddaf9 100644
--- a/lib/exec.c
+++ b/lib/exec.c
@@ -972,7 +972,7 @@ static HCL_INLINE int call_primitive (hcl_t* hcl, hcl_ooi_t nargs)
 		return -1;
 	}
 
-	return ((hcl_pfimpl_t)rcv->slot[0]) (hcl, nargs);
+	return ((hcl_pfimpl_t)rcv->slot[0]) (hcl, (hcl_mod_t*)rcv->slot[4], nargs);
 }
 
 /* ------------------------------------------------------------------------- */
diff --git a/lib/hcl-prv.h b/lib/hcl-prv.h
index 0bc71c9..88429b8 100644
--- a/lib/hcl-prv.h
+++ b/lib/hcl-prv.h
@@ -1028,7 +1028,8 @@ void hcl_closemod (
 hcl_pfbase_t* hcl_querymod (
 	hcl_t*            hcl,
 	const hcl_ooch_t* pfid,
-	hcl_oow_t         pfidlen
+	hcl_oow_t         pfidlen,
+	hcl_mod_t**       mod
 );
 
 /* ========================================================================= */
diff --git a/lib/hcl.c b/lib/hcl.c
index d338b5a..3bf4385 100644
--- a/lib/hcl.c
+++ b/lib/hcl.c
@@ -619,7 +619,7 @@ void hcl_closemod (hcl_t* hcl, hcl_mod_data_t* mdp)
 	}
 }
 
-hcl_pfbase_t* hcl_querymod (hcl_t* hcl, const hcl_ooch_t* pfid, hcl_oow_t pfidlen)
+hcl_pfbase_t* hcl_querymod (hcl_t* hcl, const hcl_ooch_t* pfid, hcl_oow_t pfidlen, hcl_mod_t** mod)
 {
 	/* primitive function identifier
 	 *   _funcname
@@ -650,7 +650,7 @@ hcl_pfbase_t* hcl_querymod (hcl_t* hcl, const hcl_ooch_t* pfid, hcl_oow_t pfidle
 	 * module id. the last segment is the primitive function name.
 	 * for instance, in con.window.open, con.window is a module id and
 	 * open is the primitive function name. */
-	pair = hcl_rbt_search (&hcl->modtab, pfid, mod_name_len);
+	pair = hcl_rbt_search(&hcl->modtab, pfid, mod_name_len);
 	if (pair)
 	{
 		mdp = (hcl_mod_data_t*)HCL_RBT_VPTR(pair);
@@ -659,11 +659,11 @@ hcl_pfbase_t* hcl_querymod (hcl_t* hcl, const hcl_ooch_t* pfid, hcl_oow_t pfidle
 	else
 	{
 		/* open a module using the part before the last period */
-		mdp = hcl_openmod (hcl, pfid, mod_name_len);
+		mdp = hcl_openmod(hcl, pfid, mod_name_len);
 		if (!mdp) return HCL_NULL;
 	}
 
-	if ((pfbase = mdp->mod.query (hcl, &mdp->mod, sep + 1, pfidlen - mod_name_len - 1)) == HCL_NULL) 
+	if ((pfbase = mdp->mod.query(hcl, &mdp->mod, sep + 1, pfidlen - mod_name_len - 1)) == HCL_NULL) 
 	{
 		/* the primitive function is not found. but keep the module open even if it's opened above */
 		HCL_DEBUG3 (hcl, "Cannot find a primitive function [%.*js] in a module [%js]\n", pfidlen - mod_name_len - 1, sep + 1, mdp->mod.name);
@@ -671,6 +671,8 @@ hcl_pfbase_t* hcl_querymod (hcl_t* hcl, const hcl_ooch_t* pfid, hcl_oow_t pfidle
 		return HCL_NULL;
 	}
 
+	*mod = &mdp->mod;
+
 	HCL_DEBUG4 (hcl, "Found a primitive function [%.*js] in a module [%js] - %p\n",
 		pfidlen - mod_name_len - 1, sep + 1, mdp->mod.name, pfbase);
 	return pfbase;
diff --git a/lib/hcl.h b/lib/hcl.h
index e0a5a63..c93900b 100644
--- a/lib/hcl.h
+++ b/lib/hcl.h
@@ -35,6 +35,10 @@
 
 /* ========================================================================== */
 
+typedef struct hcl_mod_t hcl_mod_t;
+
+/* ========================================================================== */
+
 /**
  * The hcl_errnum_t type defines the error codes.
  */
@@ -835,7 +839,10 @@ enum hcl_pfrc_t
 };
 typedef enum hcl_pfrc_t hcl_pfrc_t;
 
-typedef hcl_pfrc_t (*hcl_pfimpl_t) (hcl_t* hcl, hcl_ooi_t nargs);
+typedef hcl_pfrc_t (*hcl_pfimpl_t) (
+	hcl_t*     hcl,
+	hcl_mod_t* mod,
+	hcl_ooi_t  nargs);
 
 
 typedef struct hcl_pfbase_t hcl_pfbase_t;
@@ -858,8 +865,6 @@ struct hcl_pfinfo_t
  * ========================================================================= */
 #define HCL_MOD_NAME_LEN_MAX 120
 
-typedef struct hcl_mod_t hcl_mod_t;
-
 typedef int (*hcl_mod_load_t) (
 	hcl_t*     hcl,
 	hcl_mod_t* mod
@@ -1692,7 +1697,8 @@ HCL_EXPORT hcl_oop_t hcl_makeprim (
 	hcl_t*          hcl,
 	hcl_pfimpl_t    primimpl,
 	hcl_oow_t       minargs,
-	hcl_oow_t       maxargs
+	hcl_oow_t       maxargs,
+	hcl_mod_t*      mod
 );
 
 
diff --git a/lib/main.c b/lib/main.c
index b1cf6cc..4769c1d 100644
--- a/lib/main.c
+++ b/lib/main.c
@@ -1623,7 +1623,6 @@ int main (int argc, char* argv[])
 			else
 			{
 				hcl_logbfmt (hcl, HCL_LOG_STDERR, "ERROR: cannot read object - [%d] %js\n", hcl_geterrnum(hcl), hcl_geterrmsg(hcl));
-				
 			}
 			goto oops;
 		}
diff --git a/lib/prim.c b/lib/prim.c
index 031482d..80949bb 100644
--- a/lib/prim.c
+++ b/lib/prim.c
@@ -39,16 +39,17 @@ typedef struct pf_t pf_t;
 
 /* ------------------------------------------------------------------------- */
 
-hcl_oop_t hcl_makeprim (hcl_t* hcl, hcl_pfimpl_t primimpl, hcl_oow_t minargs, hcl_oow_t maxargs)
+hcl_oop_t hcl_makeprim (hcl_t* hcl, hcl_pfimpl_t primimpl, hcl_oow_t minargs, hcl_oow_t maxargs, hcl_mod_t* mod)
 {
 	hcl_oop_word_t obj;
 
-	obj = (hcl_oop_word_t)hcl_allocwordobj (hcl, HCL_BRAND_PRIM, HCL_NULL, 3);
+	obj = (hcl_oop_word_t)hcl_allocwordobj (hcl, HCL_BRAND_PRIM, HCL_NULL, 4);
 	if (obj)
 	{
 		obj->slot[0] = (hcl_oow_t)primimpl;
 		obj->slot[1] = minargs;
 		obj->slot[2] = maxargs;
+		obj->slot[4] = (hcl_oow_t)mod;
 	}
 
 	return (hcl_oop_t)obj;
@@ -94,7 +95,7 @@ start_over:
 	}
 }
 
-static hcl_pfrc_t pf_log (hcl_t* hcl, hcl_ooi_t nargs)
+static hcl_pfrc_t pf_log (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 {
 /* TODO: accept log level */
 	hcl_oop_t msg;
@@ -166,7 +167,7 @@ static hcl_pfrc_t pf_log (hcl_t* hcl, hcl_ooi_t nargs)
 	return HCL_PF_SUCCESS;
 }
 
-static hcl_pfrc_t pf_gc (hcl_t* hcl, hcl_ooi_t nargs)
+static hcl_pfrc_t pf_gc (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 {
 	hcl_gc (hcl);
 	HCL_STACK_SETRET (hcl, nargs, hcl->_nil);
@@ -174,7 +175,7 @@ static hcl_pfrc_t pf_gc (hcl_t* hcl, hcl_ooi_t nargs)
 }
 
 /* ------------------------------------------------------------------------- */
-static hcl_pfrc_t pf_eqv (hcl_t* hcl, hcl_ooi_t nargs)
+static hcl_pfrc_t pf_eqv (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 {
 	hcl_oop_t a0, a1, rv;
 
@@ -187,7 +188,7 @@ static hcl_pfrc_t pf_eqv (hcl_t* hcl, hcl_ooi_t nargs)
 	return HCL_PF_SUCCESS;
 }
 
-static hcl_pfrc_t pf_eql (hcl_t* hcl, hcl_ooi_t nargs)
+static hcl_pfrc_t pf_eql (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 {
 	int n;
 	n = hcl_equalobjs(hcl, HCL_STACK_GETARG(hcl, nargs, 0), HCL_STACK_GETARG(hcl, nargs, 1));
@@ -197,7 +198,7 @@ static hcl_pfrc_t pf_eql (hcl_t* hcl, hcl_ooi_t nargs)
 	return HCL_PF_SUCCESS;
 }
 
-static hcl_pfrc_t pf_eqk (hcl_t* hcl, hcl_ooi_t nargs)
+static hcl_pfrc_t pf_eqk (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 {
 	/* equal kind? */
 	hcl_oop_t a0, a1, rv;
@@ -211,7 +212,7 @@ static hcl_pfrc_t pf_eqk (hcl_t* hcl, hcl_ooi_t nargs)
 	return HCL_PF_SUCCESS;
 }
 
-static hcl_pfrc_t pf_not (hcl_t* hcl, hcl_ooi_t nargs)
+static hcl_pfrc_t pf_not (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 {
 	hcl_oop_t arg, rv;
 
@@ -228,7 +229,7 @@ static hcl_pfrc_t pf_not (hcl_t* hcl, hcl_ooi_t nargs)
 	return HCL_PF_SUCCESS;
 }
 
-static hcl_pfrc_t pf_and (hcl_t* hcl, hcl_ooi_t nargs)
+static hcl_pfrc_t pf_and (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 {
 	hcl_oop_t arg, rv;
 	hcl_ooi_t i;
@@ -257,7 +258,7 @@ static hcl_pfrc_t pf_and (hcl_t* hcl, hcl_ooi_t nargs)
 	return HCL_PF_SUCCESS;
 }
 
-static hcl_pfrc_t pf_or (hcl_t* hcl, hcl_ooi_t nargs)
+static hcl_pfrc_t pf_or (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 {
 	hcl_oop_t arg, rv;
 	hcl_ooi_t i;
@@ -288,7 +289,7 @@ static hcl_pfrc_t pf_or (hcl_t* hcl, hcl_ooi_t nargs)
 
 /* ------------------------------------------------------------------------- */
 
-static hcl_pfrc_t pf_integer_add (hcl_t* hcl, hcl_ooi_t nargs)
+static hcl_pfrc_t pf_integer_add (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 {
 	hcl_ooi_t i;
 	hcl_oop_t arg, ret;
@@ -305,7 +306,7 @@ static hcl_pfrc_t pf_integer_add (hcl_t* hcl, hcl_ooi_t nargs)
 	return HCL_PF_SUCCESS;
 }
 
-static hcl_pfrc_t pf_integer_sub (hcl_t* hcl, hcl_ooi_t nargs)
+static hcl_pfrc_t pf_integer_sub (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 {
 	hcl_ooi_t i;
 	hcl_oop_t arg, ret;
@@ -322,7 +323,7 @@ static hcl_pfrc_t pf_integer_sub (hcl_t* hcl, hcl_ooi_t nargs)
 	return HCL_PF_SUCCESS;
 }
 
-static hcl_pfrc_t pf_integer_mul (hcl_t* hcl, hcl_ooi_t nargs)
+static hcl_pfrc_t pf_integer_mul (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 {
 	hcl_ooi_t i;
 	hcl_oop_t arg, ret;
@@ -339,7 +340,7 @@ static hcl_pfrc_t pf_integer_mul (hcl_t* hcl, hcl_ooi_t nargs)
 	return HCL_PF_SUCCESS;
 }
 
-static hcl_pfrc_t pf_integer_quo (hcl_t* hcl, hcl_ooi_t nargs)
+static hcl_pfrc_t pf_integer_quo (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 {
 	hcl_ooi_t i;
 	hcl_oop_t arg, ret;
@@ -356,7 +357,7 @@ static hcl_pfrc_t pf_integer_quo (hcl_t* hcl, hcl_ooi_t nargs)
 	return HCL_PF_SUCCESS;
 }
 
-static hcl_pfrc_t pf_integer_rem (hcl_t* hcl, hcl_ooi_t nargs)
+static hcl_pfrc_t pf_integer_rem (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 {
 	hcl_ooi_t i;
 	hcl_oop_t arg, ret, rem;
@@ -377,7 +378,7 @@ static hcl_pfrc_t pf_integer_rem (hcl_t* hcl, hcl_ooi_t nargs)
 /* ------------------------------------------------------------------------- */
 
 
-static hcl_pfrc_t pf_printf (hcl_t* hcl, hcl_ooi_t nargs)
+static hcl_pfrc_t pf_printf (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 {
 	hcl_oop_char_t fmt;
 
@@ -444,7 +445,7 @@ int hcl_addbuiltinprims (hcl_t* hcl)
 
 	for (i = 0; i < HCL_COUNTOF(builtin_prims); i++)
 	{
-		prim = hcl_makeprim(hcl, builtin_prims[i].impl, builtin_prims[i].minargs, builtin_prims[i].maxargs);
+		prim = hcl_makeprim(hcl, builtin_prims[i].impl, builtin_prims[i].minargs, builtin_prims[i].maxargs, HCL_NULL);
 		if (!prim) return -1;
 
 		hcl_pushtmp (hcl, &prim);
diff --git a/lib/read.c b/lib/read.c
index a4814db..73826dd 100644
--- a/lib/read.c
+++ b/lib/read.c
@@ -2077,9 +2077,10 @@ static int read_object (hcl_t* hcl)
 				if (obj)
 				{
 					hcl_pfbase_t* pfbase;
+					hcl_mod_t* mod;
 					hcl_oop_t prim;
 
-					pfbase = hcl_querymod(hcl, TOKEN_NAME_PTR(hcl), TOKEN_NAME_LEN(hcl));
+					pfbase = hcl_querymod(hcl, TOKEN_NAME_PTR(hcl), TOKEN_NAME_LEN(hcl), &mod);
 					if (!pfbase)
 					{
 						/* TODO switch to syntax error */
@@ -2087,7 +2088,7 @@ static int read_object (hcl_t* hcl)
 					}
 
 					hcl_pushtmp (hcl, &obj);
-					prim = hcl_makeprim(hcl, pfbase->handler, pfbase->minargs, pfbase->maxargs);
+					prim = hcl_makeprim(hcl, pfbase->handler, pfbase->minargs, pfbase->maxargs, mod);
 
 					if (!prim || !hcl_putatsysdic(hcl, obj, prim))
 					{
diff --git a/mod/arr.c b/mod/arr.c
index 41195f0..11786a5 100644
--- a/mod/arr.c
+++ b/mod/arr.c
@@ -27,7 +27,7 @@
 
 #include "_arr.h"
 
-static hcl_pfrc_t pf_arr_get (hcl_t* hcl, hcl_ooi_t nargs)
+static hcl_pfrc_t pf_arr_get (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 {
 	hcl_oop_oop_t arr;
 	hcl_oop_t idx;
@@ -54,7 +54,7 @@ static hcl_pfrc_t pf_arr_get (hcl_t* hcl, hcl_ooi_t nargs)
 	return HCL_PF_SUCCESS;
 }
 
-static hcl_pfrc_t pf_arr_put (hcl_t* hcl, hcl_ooi_t nargs)
+static hcl_pfrc_t pf_arr_put (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 {
 	hcl_oop_oop_t arr;
 	hcl_oop_t idx, val;
@@ -83,7 +83,7 @@ static hcl_pfrc_t pf_arr_put (hcl_t* hcl, hcl_ooi_t nargs)
 	return HCL_PF_SUCCESS;
 }
 
-static hcl_pfrc_t pf_arr_size (hcl_t* hcl, hcl_ooi_t nargs)
+static hcl_pfrc_t pf_arr_size (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 {
 	hcl_oop_oop_t arr;
 	hcl_oop_t size;
diff --git a/mod/dic.c b/mod/dic.c
index b90bed6..ed84a75 100644
--- a/mod/dic.c
+++ b/mod/dic.c
@@ -27,7 +27,7 @@
 
 #include "_dic.h"
 
-static hcl_pfrc_t pf_dic_get (hcl_t* hcl, hcl_ooi_t nargs)
+static hcl_pfrc_t pf_dic_get (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 {
 	hcl_oop_t dic;
 	hcl_oop_t key;
@@ -54,7 +54,7 @@ static hcl_pfrc_t pf_dic_get (hcl_t* hcl, hcl_ooi_t nargs)
 }
 
 
-static hcl_pfrc_t pf_dic_put (hcl_t* hcl, hcl_ooi_t nargs)
+static hcl_pfrc_t pf_dic_put (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 {
 	hcl_oop_t dic;
 	hcl_oop_t key, val;
@@ -88,7 +88,7 @@ static int walker (hcl_t* hcl, hcl_oop_dic_t dic, hcl_oop_cons_t pair, void* ctx
 	return 0;
 }
 
-static hcl_pfrc_t pf_dic_walk (hcl_t* hcl, hcl_ooi_t nargs)
+static hcl_pfrc_t pf_dic_walk (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 {
 /* TODO: write a proper function 
  * (dic.apply #{ ... } callable-or-lambda)
diff --git a/mod/str.c b/mod/str.c
index b6b769f..4ceca9b 100644
--- a/mod/str.c
+++ b/mod/str.c
@@ -27,7 +27,7 @@
 
 #include "_str.h"
 
-static hcl_pfrc_t pf_str_length (hcl_t* hcl, hcl_ooi_t nargs)
+static hcl_pfrc_t pf_str_length (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 {
 	hcl_oop_t str;
 	hcl_ooi_t size;