GN_Xnx, index next entry in linked list

RST 20H, DEFW $4409

IN:

     CDE = pointer to previous entry
     BHL = pointer to current entry

     Fc = 0
     CDE = pointer to old current entry (ie. BHL(in))
     BHL = pointer to next entry
     Fz = 1, if BHL(out) = 0.

     Fc = 1
          If BHL(in) = 0; BHL(in) and CDE(in) are then preserved.
     A = error code:
          RC_EOF ($09), attempt to step beyond start or end of list

     ......../IXIY same
     AFBCDEHL/.... different

Bugs:
 

Related calls:

GN_Xdl, delete an entry from a linked list
GN_Xin, insert an entry into a linked list