// scan a list of items in a file
Set seenItems = newSet();
FILE *in = fopen(FileName,"r");
while (fscanf(in, "%d", &item) == 1) {
   if (SetMember(seenItems, item))
      // ignore, already processed;
   else {
      SetInsert(seenItems, item);
      process item;
   }
}
fclose(in);