diff --git a/include/extra/array.h b/include/extra/array.h
index fd662a9..f720a78 100644
--- a/include/extra/array.h
+++ b/include/extra/array.h
@@ -17,6 +17,6 @@ extern ssize_t libcdsb_array_get(vtype_value* x, vtype_array* s, ssize_t index,
 extern ssize_t libcdsb_array_find(const vtype_array* x, const void* value, vtype value_type) LIBCDSB_nt__ LIBCDSB_nn1__;
 extern ssize_t libcdsb_array_push(      vtype_array* x, const void* value, vtype value_type) LIBCDSB_nt__ LIBCDSB_nn1__;
 
-extern int libcdsb_array_foreach(const vtype_array* x, int (*callback)(void* value, ssize_t index, vtype type)) LIBCDSB_nt__ LIBCDSB_nn12__;
+extern int libcdsb_array_foreach(const vtype_array* x, void* data, int (*callback)(void* value, ssize_t index, vtype type, void* data)) LIBCDSB_nt__ LIBCDSB_nn13__;
 
 #endif /* LIBCDSB_EXTRA_ARRAY_H */
diff --git a/include/extra/list.h b/include/extra/list.h
index 6ef3c89..a227b0e 100644
--- a/include/extra/list.h
+++ b/include/extra/list.h
@@ -19,6 +19,6 @@ extern size_t  libcdsb_list_count(const vtype_list* s, const void* value, vtype
 
 extern ssize_t libcdsb_list_get(vtype_value* x, vtype_list* s, ssize_t index, _Bool cut) LIBCDSB_nt__ LIBCDSB_nn2__;
 
-extern int libcdsb_list_foreach(const vtype_list* x, int (*callback)(void* value, ssize_t index, vtype type)) LIBCDSB_nt__ LIBCDSB_nn12__;
+extern int libcdsb_list_foreach(const vtype_list* x, void* data, int (*callback)(void* value, ssize_t index, vtype type, void* data)) LIBCDSB_nt__ LIBCDSB_nn13__;
 
 #endif /* LIBCDSB_EXTRA_LIST_H */
diff --git a/include/extra/set.h b/include/extra/set.h
index 80fabf9..7f37db5 100644
--- a/include/extra/set.h
+++ b/include/extra/set.h
@@ -11,6 +11,6 @@
 extern _Bool libcdsb_vset_find  (vtype_value* x, vtype_set* s, const void* value, vtype type, _Bool cut);
 extern _Bool libcdsb_vset_insert(vtype_set*   x, const void* value, vtype type);
 
-extern int libcdsb_vset_foreach(const vtype_set* x, int (*callback)(const void* value, vtype type)) LIBCDSB_nt__ LIBCDSB_nn12__;
+extern int libcdsb_vset_foreach(const vtype_set* x, void* data, int (*callback)(const void* value, vtype type, void* data)) LIBCDSB_nt__ LIBCDSB_nn13__;
 
 #endif /* LIBCDSB_EXTRA_SET_H */
diff --git a/src/array/extra.c b/src/array/extra.c
index 211d423..4486800 100644
--- a/src/array/extra.c
+++ b/src/array/extra.c
@@ -76,7 +76,7 @@ ssize_t libcdsb_array_get(val_t* x, arr_t* s, ssize_t i, _Bool cut) {
 
 /*#####################################################################################################################*/
 
-int libcdsb_array_foreach(const vtype_array* x, int (*callback)(void* value, ssize_t index, vtype type)) {
+int libcdsb_array_foreach(const vtype_array* x, void* data, int (*callback)(void* value, ssize_t index, vtype type, void* data)) {
 
     void*  p;
     void*  e;
@@ -88,7 +88,7 @@ int libcdsb_array_foreach(const vtype_array* x, int (*callback)(void* value, ssi
     n = 0;
 
     while (p < e) {
-        if ((r = callback(p, n, x->type)))
+        if ((r = callback(p, n, x->type, data)))
             return r;
 
         p += vtype_size(x->type);
diff --git a/src/list/extra.c b/src/list/extra.c
index 570b679..9e8405c 100644
--- a/src/list/extra.c
+++ b/src/list/extra.c
@@ -163,7 +163,7 @@ _Bool libcdsb_list_update(list_t* x, ssize_t i, const void* v, vtype t, int ins)
 /*#####################################################################################################################*/
 
 
-int libcdsb_list_foreach(const vtype_list* x, int (*callback)(void* value, ssize_t index, vtype type)) {
+int libcdsb_list_foreach(const vtype_list* x, void* data, int (*callback)(void* value, ssize_t index, vtype type, void* data)) {
 
     lnode_t* c;
     size_t   n;
@@ -173,7 +173,7 @@ int libcdsb_list_foreach(const vtype_list* x, int (*callback)(void* value, ssize
     n = 0;
 
     while (!is_null(c)) {
-        if ((r = callback(vnode_peek(&c->node, c->type), n, c->type)) != 0)
+        if ((r = callback(vnode_peek(&c->node, c->type), n, c->type, data)) != 0)
             return r;
         c = c->next;
         ++n;
diff --git a/src/set/extra.c b/src/set/extra.c
index 3c3be91..9acc2d1 100644
--- a/src/set/extra.c
+++ b/src/set/extra.c
@@ -76,17 +76,23 @@ _Bool libcdsb_vset_insert(set_t* x, const void* v, vtype t) {
 /*#####################################################################################################################*/
 
 
-int libcdsb_vset_foreach(const vtype_set* x, int (*callback)(const void* value, vtype type)) {
-    rbiter_t i;
-    int      r;
+int libcdsb_vset_foreach(const set_t* x, void* data, int (*callback)(const void* value, vtype type, void* data)) {
+    stack_t   s = { .prev = 0, .value = x->root };
+    int       r = 0;
     rbnode_t* c;
 
-    if (rbiter_init(&i, &x->root, 0)) {
-        while (!rbnode_is_empty(c = rbiter_next(&i))) {
-            if ((r = callback(vnode_peek(&c->value, x->type), x->type)))
-                return r;
+    if (rbnode_is_empty(x->root)) return 0;
+
+    while ((c = stack_pop(&s))) {
+        if ((r = callback(vnode_peek(&c->value, x->type), x->type, data))) {
+            stack_flush(&s);
+            break;
         }
+        if (!rbnode_is_empty(c->left))
+            stack_push(&s, c->left);
+        if (!rbnode_is_empty(c->right))
+            stack_push(&s, c->right);
     }
 
-    return 0;
+    return r;
 }