diff --git a/doc/stdlib_data.md b/doc/stdlib_data.md
index 5be753b..7e02bf6 100644
--- a/doc/stdlib_data.md
+++ b/doc/stdlib_data.md
@@ -11,15 +11,29 @@ These functions operate on various data structures in Keithlisp.
 ```
 (car cons)
 ```
-`car` returns the `car` portion of `cons`, or nil if the argument is not
-a cons.
+`car` returns the car portion of `cons`, or nil if the argument is not a
+cons.
 
 ## `cdr`
 ```
 (cdr cons)
 ```
-`cdr` returns the `cdr` portion of `cons`, or nil if the argument is not
-a cons.
+`cdr` returns the cdr portion of `cons`, or nil if the argument is not a
+cons.
+
+## `rplaca`
+```
+(rplaca cons value)
+```
+`rplaca` changes the car portion of `cons` to `value`. It returns the
+same `cons` it was given.
+
+## `rplacd`
+```
+(rplacd cons value)
+```
+`rplacd` changes the cdr portion of `cons` to `value`. It returns the
+same `cons` it was given.
 
 ## `list`
 ```
@@ -32,16 +46,63 @@ a cons.
 (length list)
 ```
 `length` returns the length of `list`, or nil if it is not a valid list.
-If `list` is circular, `length` may never return.
+**If `list` is circular, `length` will go into an infinite loop.**
 
 ## `nth`
 ```
 (nth index list)
 ```
-Returns the `index`th element in `list`. `index` must be an int.
+`nth` returns the `index`th element in `list`. `index` must be an int.
+
+If `index` is negative, `nth` will add `(length list)` to it. **This
+will fail if `list` is circular.**
 
 ## `nthcdr`
 ```
 (nthcdr index list)
 ```
-Returns the cdr of the `index`th cons in `list`. `index` must be an int.
+`nthcdr` returns the cdr of the `index`th cons in `list`. `index` must
+be an int.
+
+If `index` is negative, `nthcdr` will add `(length list)` to it. **This
+will fail if `list` is circular.**
+
+## `append`
+```
+(append &rest lists)
+```
+`append` constructs a new list containing all the elements of `lists`
+appended together. It makes a shallow copy of each of its arguments.
+
+## `push`
+```
+(push list item)
+```
+`push` pushes `item` onto `list` and returns the new head of `list`.
+
+## `assoc`
+```
+(assoc alist key)
+```
+`assoc` returns the first cons in `alist` whose car is
+[`eq`](stdlib_comparison.md#eq) to `key`, or nil if no matching cons
+was found.
+
+## `rassoc`
+```
+(rassoc alist value)
+```
+`rassoc` returns the first cons in `alist` whose cdr is
+[`eq`](stdlib_comparison.md#eq) to `value`, or nil if no matching cons
+was found.
+
+## `alist-put`
+```
+(alist-put alist key value)
+```
+`alist-put` creates a new cons mapping `key` to `value`, and attempts to
+update `alist` with it in-place. If `alist` already contains a cons
+whose car is [`eq`](stdlib_comparison.md#eq) to `key`, the cons is
+replaced in-place with the new one. Otherwise, `alist-put` pushes the
+new cons onto `alist` and returns the new head of `alist`, in the same
+manner as [`push`](stdlib_data.md#push).
diff --git a/lisp_types.h b/lisp_types.h
index 4125d74..7c2e591 100644
--- a/lisp_types.h
+++ b/lisp_types.h
@@ -26,7 +26,7 @@ struct lisp_value {
 		lisp_native_fun funptr;
 	} value;
 	char type;
-	bool gc;
+	//bool gc;
 } __attribute__((packed));
 
 struct lisp_cons {
diff --git a/native_funs.c b/native_funs.c
index 6af2e5f..e9adab4 100644
--- a/native_funs.c
+++ b/native_funs.c
@@ -376,6 +376,18 @@ void lispf_cdr(lisp_cons* cons, lisp_value* value) {
 		return;
 	*value = cons->car.value.cons->cdr;
 }
+void lispf_rplaca(lisp_cons* cons, lisp_value* value) {
+	if (cons->car.type != LISP_T_CONS || lisp_is_nil(cons->car))
+		return;
+	cons->car.value.cons->car = cons->cdr.value.cons->car;
+	*value = cons->car;
+}
+void lispf_rplacd(lisp_cons* cons, lisp_value* value) {
+	if (cons->car.type != LISP_T_CONS || lisp_is_nil(cons->car))
+		return;
+	cons->car.value.cons->cdr = cons->cdr.value.cons->car;
+	*value = cons->car;
+}
 
 void lispf_list(lisp_cons* cons, lisp_value* value) {
 	lisp_cons* head = NULL;
@@ -416,11 +428,19 @@ void lispf_nth(lisp_cons* cons, lisp_value* value) {
 	if (cons->car.type != LISP_T_INT)
 		return;
 	int index = cons->car.value._int;
+	if (index < 0) {
+		// index is negative, call lispf_length
+		lisp_value temp;
+		lispf_length(cons->cdr.value.cons, &temp);
+		index += temp.value._int;
+	}
 	lisp_cons* head = cons->cdr.value.cons->car.value.cons;
+	if (head == NULL)
+		return;
 	while (index > 0) {
+		head = head->cdr.value.cons;
 		if (head == NULL)
 			return;
-		head = head->cdr.value.cons;
 		index--;
 	}
 	*value = head->car;
@@ -429,14 +449,100 @@ void lispf_nthcdr(lisp_cons* cons, lisp_value* value) {
 	if (cons->car.type != LISP_T_INT)
 		return;
 	int index = cons->car.value._int;
+	if (index < 0) {
+		// index is negative, call lispf_length
+		lisp_value temp;
+		lispf_length(cons->cdr.value.cons, &temp);
+		index += temp.value._int;
+	}
 	lisp_cons* head = cons->cdr.value.cons->car.value.cons;
+	if (head == NULL)
+		return;
 	while (index > 0) {
+		head = head->cdr.value.cons;
 		if (head == NULL)
 			return;
-		head = head->cdr.value.cons;
 		index--;
 	}
-	*value = head->cdr;
+	value->type = LISP_T_CONS;
+	value->value.cons = head;
+}
+void lispf_append(lisp_cons* cons, lisp_value* value) {
+	lisp_cons* head = NULL;
+	lisp_cons* tail = NULL;
+
+	while (cons != NULL) {
+		if (cons->cdr.value.cons == NULL && cons->car.type != LISP_T_CONS) {
+			tail->cdr = cons->car;
+			break;
+		} else {
+			lisp_cons* subcons = cons->car.value.cons;
+			while (subcons != NULL) {
+				lisp_cons* element = dbg_malloc(sizeof(lisp_cons));
+				element->car = subcons->car;
+				element->cdr.type = LISP_T_CONS;
+				element->cdr.value.cons = NULL;
+
+				if (head == NULL)
+					head = element;
+				if (tail != NULL)
+					tail->cdr.value.cons = element;
+
+				tail = element;
+				subcons = subcons->cdr.value.cons;
+			}
+			cons = cons->cdr.value.cons;
+		}
+	}
+
+	value->type = LISP_T_CONS;
+	value->value.cons = head;
+}
+void lispf_push(lisp_cons* cons, lisp_value* value) {
+	lisp_cons* list = cons->car.value.cons;
+	lisp_value item = cons->cdr.value.cons->car;
+
+	value->type = LISP_T_CONS;
+	value->value.cons = dbg_malloc(sizeof(lisp_cons));
+	value->value.cons->car = item;
+	value->value.cons->cdr.type = LISP_T_CONS;
+	value->value.cons->cdr.value.cons = list;
+}
+
+void lispf_assoc(lisp_cons* cons, lisp_value* value) {
+	lisp_cons* alist = cons->car.value.cons;
+	lisp_value key = cons->cdr.value.cons->car;
+	value->type = LISP_T_CONS;
+	value->value.cons = lisp_alist_get(alist, key);
+}
+void lispf_rassoc(lisp_cons* cons, lisp_value* value) {
+	lisp_cons* alist = cons->car.value.cons;
+	lisp_value cdr_key = cons->cdr.value.cons->car;
+	value->type = LISP_T_CONS;
+	while (alist != NULL) {
+		if (alist->car.type != LISP_T_CONS || alist->car.value.cons == NULL)
+			goto next;
+		value->value.cons = alist->car.value.cons;
+		if (lisp_is_equal(value->value.cons->cdr, cdr_key))
+			return;
+	next:
+		if (alist->cdr.type == LISP_T_CONS)
+			alist = alist->cdr.value.cons;
+		else
+			alist = NULL;
+	}
+}
+void lispf_alist_put(lisp_cons* cons, lisp_value* value) {
+	value->type = LISP_T_CONS;
+	value->value.cons = cons->car.value.cons;
+	lisp_value key = cons->cdr.value.cons->car;
+	lisp_value new_value = cons->cdr.value.cons->cdr.value.cons->car;
+
+	lisp_cons* pair = dbg_malloc(sizeof(lisp_cons));
+	pair->car = key;
+	pair->cdr = new_value;
+
+	lisp_cons* old_pair = lisp_alist_put(&value->value.cons, pair);
 }
 
 void lispf_type_of(lisp_cons* cons, lisp_value* value) {
@@ -560,11 +666,19 @@ void init_native_funs() {
 	lisp_defun_native(lisp_string_create("cons"), &lispf_cons);
 	lisp_defun_native(lisp_string_create("car"), &lispf_car);
 	lisp_defun_native(lisp_string_create("cdr"), &lispf_cdr);
+	lisp_defun_native(lisp_string_create("rplaca"), &lispf_rplaca);
+	lisp_defun_native(lisp_string_create("rplacd"), &lispf_rplacd);
 
 	lisp_defun_native(lisp_string_create("list"), &lispf_list);
 	lisp_defun_native(lisp_string_create("length"), &lispf_length);
 	lisp_defun_native(lisp_string_create("nth"), &lispf_nth);
 	lisp_defun_native(lisp_string_create("nthcdr"), &lispf_nthcdr);
+	lisp_defun_native(lisp_string_create("append"), &lispf_append);
+	lisp_defun_native(lisp_string_create("push"), &lispf_push);
+
+	lisp_defun_native(lisp_string_create("assoc"), &lispf_assoc);
+	lisp_defun_native(lisp_string_create("rassoc"), &lispf_rassoc);
+	lisp_defun_native(lisp_string_create("alist-put"), &lispf_alist_put);
 
 	// etc
 	lisp_defun_native(lisp_string_create("type-of"), &lispf_type_of);
diff --git a/native_funs.h b/native_funs.h
index bcfa27f..151987e 100644
--- a/native_funs.h
+++ b/native_funs.h
@@ -28,11 +28,19 @@ void lispf_num_ge(lisp_cons* cons, lisp_value* value);
 void lispf_cons(lisp_cons* cons, lisp_value* value);
 void lispf_car(lisp_cons* cons, lisp_value* value);
 void lispf_cdr(lisp_cons* cons, lisp_value* value);
+void lispf_rplaca(lisp_cons* cons, lisp_value* value);
+void lispf_rplacd(lisp_cons* cons, lisp_value* value);
 
 void lispf_list(lisp_cons* cons, lisp_value* value);
 void lispf_length(lisp_cons* cons, lisp_value* value);
 void lispf_nth(lisp_cons* cons, lisp_value* value);
 void lispf_nthcdr(lisp_cons* cons, lisp_value* value);
+void lispf_append(lisp_cons* cons, lisp_value* value);
+void lispf_push(lisp_cons* cons, lisp_value* value);
+
+void lispf_assoc(lisp_cons* cons, lisp_value* value);
+void lispf_rassoc(lisp_cons* cons, lisp_value* value);
+void lispf_alist_put(lisp_cons* cons, lisp_value* value);
 
 void lispf_type_of(lisp_cons* cons, lisp_value* value);
 void lispf_addr_of(lisp_cons* cons, lisp_value* value);