Playing with SymPy design in C

#include "stdlib.h"
#include "stdio.h"
 
//----------------------- basic ---------------------------------
 
typedef struct _basic {
    void (*print)();
 
    struct _basic *args;
    int nargs;
} basic;
 
void basic_print(basic *b)
{
    if (b->nargs != 0)
    {
        printf("basic_print nargs\n");
    }
    else
        printf("basic_print\n");
}
 
void basic_init(basic *b)
{
    b->print = basic_print;
    b->nargs = 0;
}
 
basic *basic_new()
{
    basic *b;
    b = malloc(sizeof(basic));
    basic_init(b);
    return b;
}
 
//------------------------ add  -------------------------------------------
 
typedef struct {
    basic super;
 
    int i,j;
} add;
 
void add_print(add *p)
{
    printf("add_print %d %d\n", p->i, p->j);
}
 
basic *add_new(int a, int b)
{
    add *p;
    p = malloc(sizeof(add));
    basic_init((basic *)p);
    p->super.print = add_print;
    p->super.nargs = 1;
    p->i = a;
    p->j = b;
    return (basic *)p;
}
 
 
// ------------------------------------------------------------
 
 
int main()
{
    basic *b;
    b = basic_new();
    b->print(b);
    b = add_new(1, 2);
    b->print(b);
    printf("OK");
    return 0;
}

$ ./basic 
basic_print
add_print 1 2