pcm4/stage2/include/lisp.h

#pragma once
#include <cstdint>

#define     SYMBOL_TABLE_SIZE       2048

typedef unsigned int  symbol_t;

#define     TYPE_SYMBOL     1
#define     TYPE_NUMBER     2
#define     TYPE_STRING     3
#define     TYPE_FLOAT      4
#define     TYPE_LIST       5


#define     symbolp(x)      (x->type == TYPE_SYMBOL)
#define     numberp(x)      (x->type == TYPE_NUMBER)
#define     stringp(x)      (x->type == TYPE_STRING)
#define     floatp(x)       (x->type == TYPE_FLOAT)
#define     listp(x)        (x->type == TYPE_LIST)

typedef struct cell {
    uint8_t                 type;
    union {
        struct {
            cell            *head;
            cell            *tail;
        };
        struct {
            union {
                symbol_t     sym;
                int          num;
                char        *str;
                float        fnum;
            };
        };
    };
};


symbol_t     intern_symbol(const char *s);
symbol_t     make_symbol(const char *s);

static auto NIL = make_symbol("nil");


cell  head(cell x);
cell  tail(cell x);