car, cons, add

test.c

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

#define new(a) malloc(sizeof(a))

typedef struct {
	int i;
} Atom;

Atom *make_atom(int i) {
	//Atom *a = make(
	Atom *a = new(Atom);
	a->i = i;
	return a;
}

char *atom_to_string(Atom *a, char *s) {
	sprintf(s, "%d", a->i);
}

typedef struct List {
	Atom *atom; // to wrap

	struct List *car;
	struct List *cdr;
} List;

List *make_list() {
	List *l = new(List);
	l->atom = NULL;
	l->car = NULL;
	l->cdr = NULL;
	return l;
}

List *make_int(int i) {
	List *l = make_list();
	l->atom = make_atom(i);
	return l;
}


int is_atom(List *lst) {
	return lst->atom != NULL;
}

List *car(List *lst) {
	if (lst->car == NULL) {
		printf("error");
		exit(-1);
	}
	return lst->car;
}

List *cons(List *a, List *b) {
	List *l = make_list();
	l->car = a;
	l->cdr = b;
	return l;
}

List *add(List *lst) {
	int i = 0;

	List *a = lst->car;
	List *d = lst->cdr;
	while (a != NULL) {
		printf("> %d\n", a->atom->i);
		i += a->atom->i;
		a = d->car;
		d = d->cdr;
	}

	return make_int(i);
}

int main() {
	List *nil = make_list();
	List *a = make_int(10);
	List *b = make_int(20);
	List *c = make_int(30);

	List *args = cons(a, cons(b, cons(c, nil)));
	List *ret = add(args);
	char str[100];

	atom_to_string(ret->atom, str);
	printf("%s\n", str);
}