+- testing, testing, testing
+- support integer keys for ht
+- validate arguments to interface functions
++ optimize tracing code, still too much overhead
++ use NULL instead of a sentinal node in skiplist and list
++ make the interfaces for all data structures consistent
++ make list and skiplist use string keys
++ optimize integer keys
+- ht_print()
+- iterators
+- characterize performance of data structures
+- experiment with the performance impact of not passing the hash between functions
+- experiment with embedding key is the list/skiplist nodes