typedef struct word{
    struct word *previous;
    char *name;
    uint8_t flag;
    void(*xt)();
}word;

#define STRUCT {0, "+", 0, add}
word last_word = {&(STRUCT), "-", 0, sub};

typedef struct word{
    // struct word *previous;
    char *name;
    uint8_t flag;
    void(*xt)();
} word;

word w[] = {
    { "plus", 0, add };
    { "minus", 0, sub };
    ...
};

typedef struct word{
    struct word *previous;
    char *name;
    unsigned char flag;
    void(*xt)();
} word;

word w[] = {
    { 0, "plus", 0, add },
    { &w[0], "minus", 0, minus },
    { &w[1], "product", 0, prod  }
    ...
};

typedef struct word {
    struct word *previous;
    char *name;
    uint8_t flag;
    void(*xt)();
} word;

word w1 = { 0, "plus", 0, add };
word w2 = { &w1, "minus", 0, sub };

typedef struct word {
    struct word *previous;
    char *name;
    uint8_t flag;
    void(*xt)();
} word;

word* root = malloc(sizeof(word));
*root = (word){ 0, "plus", 0, add };

word* prev = root;
root = malloc(sizeof(word));
*root = (word){ prev, "minus", 0, sub };

prev = root;
root = malloc(sizeof(word));
*root = (word){ prev, "times", 0, mult };

// ...

typedef struct word
{
    void(*xt)();
    char *name;
    uint8_t index;
    uint8_t flag;
} word;

word w[] =
{
    { 0, "plus", 0, add },
    { 1, "minus", 0, minus },
    { 2, "product", 0, prod  },
    // ...
};