#include <stdbool.h>

/* Datastructures representing s-exprs */

struct sexp_list;

enum sexp_form {
    sexp_bool,
    sexp_int,
    sexp_string,
    sexp_symbol,
    sexp_list,
};

struct sexp {
    enum sexp_form form;
    union {
        bool bool_lit;
        /* Integer literals are not directly converted to numbers */
        char *lexeme;
        struct sexp_list *list;
    };
};

struct sexp_list {
    struct sexp *elem;
    struct sexp_list *next;
};

/* Helper to create a list by appending at its end in O(1) time */
struct sexp_list_builder {
    struct sexp_list *head;
    struct sexp_list *last;
};

/* Returns false if allocation fails */
bool sexp_list_append(struct sexp_list_builder *b, struct sexp *elem);

/* If allocation fails, these functions return NULL */
struct sexp *sexp_make_bool(bool v);
struct sexp *sexp_make_int(char *lexeme);
struct sexp *sexp_make_string(char *lexeme);
struct sexp *sexp_make_symbol(char *lexeme);
struct sexp *sexp_make_list(struct sexp_list *list);

void free_sexp_list(struct sexp_list *head);
void free_sexp(struct sexp *s);