Auxiliary C Code ...

TOKEN makeif(tok, exp, thenpart, elsepart)
  TOKEN tok, exp, thenpart, elsepart;
  {  tok->tokentype = OPERATOR;  /* change tok */
     tok->whichval = IFOP;       /*   to if op */
     if (elsepart != NULL)
         elsepart->link = NULL;
     thenpart->link = elsepart;
     exp->link = thenpart;
     tok->operands = exp;
     return tok;
   }


         if               (if exp
        /                     thenpart
       / operands             elsepart)
      /
     /
    exp ------> thenpart ------> elsepart
         link             link