/* lisp.h */                                                                                                                                                                                                        
#ifndef _LISP_H                                                                                                                                                                                                     
#define _LISP_H                                                                                                                                                                                                     
                                                                                                                                                                                                                    
#define MAX_NODES 100           /* essentially, the number of fun args */                                                                                                                                           
                                                                                                                                                                                                                    
struct                                                                                                                                                                                                              
{                                                                                                                                                                                                                   
    enum { B_NODE, L_NODE } s;                                                                                                                                                                                      
    union                                                                                                                                                                                                           
    {                                                                                                                                                                                                               
        int i;                                                                                                                                                                                                      
        double d;                                                                                                                                                                                                   
        char c,                                                                                                                                                                                                     
            * s;                                                                                                                                                                                                    
        struct s_exp* n[MAX_NODES];                                                                                                                                                                                 
    } v;                                                                                                                                                                                                            
} s_exp;                                                                                                                                                                                                            
#endif