#include <stdint.h>
#include <stdlib.h>
#include <assert.h>

struct stack;

enum node_tag {
    NODE_APP,
    NODE_NUM,
    NODE_GLOBAL,
    NODE_IND,
    NODE_PACK
};

struct node_base {
    enum node_tag tag;
};

struct node_app {
    struct node_base base;
    struct node_base* left;
    struct node_base* right;
};

struct node_num {
    struct node_base base;
    int32_t value;
};

struct node_global {
    struct node_base base;
    int32_t arity;
    void (*function)(struct stack*);
};

struct node_ind {
    struct node_base base;
    struct node_base* next;
};

struct node_data {
    struct node_base base;
    int8_t tag;
    struct node_base** array;
};

struct node_base* alloc_node() {
    struct node_base* new_node = malloc(sizeof(struct node_app));
    assert(new_node != NULL);
    return new_node;
}

struct stack {
    size_t size;
    size_t count;
    struct node_base** data;
};

void stack_init(struct stack* s) {
    s->size = 0;
    s->count = 0;
    s->data = malloc(sizeof(*s->data) * s->size);
    assert(s->data != NULL);
}

void stack_free(struct stack* s) {
    free(s->data);
}

void stack_push(struct stack* s, struct node_base* n) {
    while(s->count >= s->size) {
        s->data = realloc(s->data, sizeof(*s->data) * (s->size *= 2));
        assert(s->data != NULL);
    }
    s->data[s->count++] = n;
}

struct node_base* stack_pop(struct stack* s) {
    assert(s->count > 0);
    s->count--;
}

struct node_base* stack_peek(struct stack* s, size_t o) {
    assert(s->count > o);
    return s->data[s->count - o - 1];
}

void stack_popn(struct stack* s, size_t n) {
    assert(s->count >= n);
    s->count -= n;
}

void stack_slide(struct stack* s, size_t n) {
    assert(s->count > n);
    s->data[s->count - n - 1] = s->data[s->count - 1];
    s->count -= n;
}

void stack_update(struct stack* s, size_t o) {
    assert(s->count > o + 1);
    struct node_ind* ind = (struct node_ind*) s->data[s->count - o - 2];
    ind->base.tag = NODE_IND;
    ind->next = s->data[s->count -= 1];
}

void stack_alloc(struct stack* s, size_t o) {
    while(o--) {
        struct node_ind* new_node = (struct node_ind*) alloc_node();
        new_node->base.tag = NODE_IND;
        new_node->next = NULL;
        stack_push(s, (struct node_base*) new_node);
    }
}

void eval(struct node_base* n);

extern void f_main(struct stack* s);

int main(int argc, char** argv) {
    struct node_global* first_node = (struct node_global*) alloc_node();
    first_node->base.tag = NODE_GLOBAL;
    first_node->arity = 0;
    first_node->function = f_main;
    eval((struct node_base*) first_node);
}