Question

I would like to delete a list and append the fore-end and back-end list and generate a new list. I have the following two structures:

typedef struct term {
   SYMBOL symbol;
   union {
       LIST termlist;
       struct term* term;
   } super;
   LIST   args;
   NAT    stamp;
   NAT    size;
} *TERM, TERM_NODE;

typedef struct LIST_HELP {
   struct LIST_HELP *cdr;
   POINTER           car;
} LIST_NODE;

typedef LIST_NODE *LIST;

Using these two structure I have a TERM like:

forall([X8,X9],implies(connected(X8,X9),exists([V],and(or(equal(h_1(X8),U),equal(h_2(X8),U)),connected(U,X9)))

Here all are symbols. Suppose if forall is a symbol then the rest act as the arguments for forall. It is a kind of Term composed of another Term. I would like to remove [V] from this and append the list before and after of it. Can you please tell me how I would do that?

Answer 1

Probably homework; so, lets say you have a list LIST l1, you find it’s cdr by l1->cdr. Now: To delete one entry from the list what you want to do is set the cdr’s cdr as the current’s cdr like so:

l1->cdr = (l1->cdr)->cdr;

You effectively deleted the entry that was previously in l1->cdr. What you also have to do is remember that previous value of l1->cdr so you can free the memory used by it.