List - Modular code

//basic.h

#ifndef BASIC_H
#define BASIC_H

#define _CRT_SECURE_NO_WARNINGS

#include <stdlib.h>
#include <stdio.h>
#include <stdbool.h>
#include <stdint.h>
#include <string.h>

typedef int element;

typedef struct list_element {
    element value;
    struct list_element *next;
}item;

typedef item* list;

extern list emptylist();
extern void showList(list l);
extern bool empty(list l);
extern element head(list l);
extern void* _abort();
extern list tail(list l);
extern list cons(element e, list l);
extern list copyList(list l);
extern void destroy(list l);
extern list insert_FIFO(element e, list l);
extern list toList(element *v, uint32_t size);
extern element* toArray(list l, size_t *sz);
extern list copyList(list l);
extern list insert();

#endif /*!BASIC_H*/

//basic.c

list emptylist()
{
    return NULL;
}

bool empty(list l)
{
    return (l == NULL);
}

element head(list l)
{
    if (empty(l)) { _abort(); return EXIT_FAILURE; }

    return l->value;
}

void* _abort()
{
    printf("\n\nIMPOSSIBILE ACCEDERE ALLA LISTA\n\n");
    return NULL;
}

list tail(list l)
{
    if (empty(l))
    {
        _abort();
        return emptylist();
    }
    else
        return l->next;
}

list cons(element e, list l)
{
    list t;

    t = malloc(sizeof(item));
    t->value = e;
    t->next = l;

    return t;
}

void showList(list l)
{
    list temp = l;

    printf("[");
    while (temp != NULL)
    {
        printf("%d", temp->value);
        if (!empty(tail(temp))) printf(", ");
        temp = tail(temp);
    }
    printf("]");
}

list insert()
{
    list l;
    uint32_t len;

    printf("Inserire il numero di elementi che si desidera inserire (il numero deve essere > di zero) : ");

    do
    {
        scanf("%d", &len);
    } while (len <= 0); printf("\n");

    l = NULL;

    for (uint32_t i = 0; i < len; i++)
    {
        int val;
        printf("\nInserire l'elemento n.%d : ", i + 1);
        scanf("%d", &val);

        l = cons(val, l);
    }

    return l;
}

void destroy(list l)
{
    while (tail(l) != NULL)
    {
        list prossimo = tail(l);
        free(l);
        l = prossimo;
    }
}

list copyList(list l)
{
    list temp = l, t = emptylist();

    while (!empty(temp))
    {
        t = insert_FIFO(head(temp), t);
        temp = tail(temp);
    }

    return t;
}

list insert_FIFO(element e, list l)
{
    list l1 = l, t, start = l;

    t = cons(e, l);
    if (empty(l)) return t;

    while (!empty(l))
    {
        l1 = l;
        l = tail(l);
    }

    l1->next = t;
    t->next = emptylist();

    return start;
}

list toList(element *v, uint32_t size)
{
    list l = emptylist();

    for (size_t i = 0; i < size; i++)
        l = cons(v[i], l);

    return l;
}

element *toArray(list l, size_t *sz)
{
    element *v = NULL;
    size_t size = 0;
    list t = l;

    while (!empty(t))
    {
        v = realloc(v, (++size) * sizeof(element));
        v[size - 1] = head(t);
        t = tail(t);
    }

    *sz = size;
    return v;
}

int main(void)
{
    return EXIT_SUCCESS;
}