Learn creating linked list in Rust style

linked_list.c

// ref: https://doc.rust-lang.org/rust-by-example/custom_types/enum/testcase_linked_list.html

#include <stdio.h>
#include <stdlib.h>

enum NodeType { Cell, Nil };

typedef struct LinkedList LinkedList;
typedef struct NodeCell {
    int car;
    LinkedList * cdr;
} NodeCell;
typedef struct NodeNil {} NodeNil;
struct LinkedList {
    enum NodeType type;
    union {
        NodeCell cell;
        NodeNil nil;
    };
};
NodeNil nil;

LinkedList * new() {
    LinkedList * seq = malloc(sizeof(LinkedList));
    seq->type = Nil;
    seq->nil = nil;
    return seq;
}

LinkedList * prepend(LinkedList * self, int element) {
    NodeCell * cell = malloc(sizeof(NodeCell));
    cell->car = element;
    cell->cdr = self;
    LinkedList * seq = malloc(sizeof(LinkedList));
    seq->type = Cell;
    seq->cell = *cell;
    return seq;
}

int len(LinkedList * self) {
    switch (self->type) {
        case Cell:
            return len(self->cell.cdr) + 1;
        case Nil:
            return 0;
    }
}

char * stringify(LinkedList * self) {
    char * buff = malloc(100 * sizeof(char));
    switch (self->type) {
        case Cell:
            snprintf(buff, 100, "%i, %s", self->cell.car, stringify(self->cell.cdr));
            return buff;
        case Nil:
            return "Nil";
    }
}

int main() {
    LinkedList * seq = new();
    for (int i = 0; i < 10; i++)
        seq = prepend(seq, i);
    printf("%i\n", len(seq));
    // 10
    printf("%s\n", stringify(seq));
    // 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, Nil
    return 0;
}