#define EOL 0
#define NUM 1
#define PLUS_OP  2
#define MINUS_OP 3

extern int tokenVal;
extern int currentToken;

void getToken(void);

typedef struct _AST {    
    int op;
    int val;
    struct _AST *left;
    struct _AST *right;
} AST;

AST *readExpr(void);