-module(htbl).         % imperative thread-safe hashtable
                       % API follows that of dict; when in doubt, look at dict
-export([new/1,        % returns new hashtable, given number of processes
	 store/3,      % store key-value pair, replacing old key mapping
	 update/4,     % update value of a key-value pair
	 find/2,       % return mapped value, or error
	 erase/2,      % erase key, value pair
	 fetch_keys/1, % return all keys
	 unit_test/0
	]).

%% -----------------------------------------------------------------------------
%% In:
%%  Nprocs: number of processes to allocate
%% Out: a new hashtable that is implemented as some number of processes (you
%%  choose) parameterized by Nprocs, allowing concurrent access similar to
%%  that which we defined for arrays in iarray.erl
%% Note: look at the erlang:phash2 built-in function
%% -----------------------------------------------------------------------------
new(Nprocs) ->
    .

%% -----------------------------------------------------------------------------
%% In:
%%  Key, Val: key-value pair to add to hashtable
%%  H: the hashtable
%% Out: (none)
%% Replaces current Key mapping if one exists.
%% -----------------------------------------------------------------------------
store(Key, Val, H) ->
    ok.

%% -----------------------------------------------------------------------------
%% In:
%%  Key: a key
%%  Fun: function value -> value to apply to existing value mapped by Key
%%  Initial: initial value if key is not mapped
%%  H: the hashtable
%% Out: (none)
%% -----------------------------------------------------------------------------
update(Key, Fun, Initial, H) ->
    ok.

%% -----------------------------------------------------------------------------
%% In:
%%  Key: a key
%%  H: the hashtable
%% Out: {ok, Value} for Value mapped by Key; or error if Key is unmapped
%% -----------------------------------------------------------------------------
find(Key, H) ->
    .

%% -----------------------------------------------------------------------------
%% In:
%%  Key: a key
%%  H: the hashtable
%% Out: (none)
%% Erase all key-value pairs for given Key.
%% -----------------------------------------------------------------------------
erase(Key, H) ->
    ok.

%% -----------------------------------------------------------------------------
%% In:
%%  H: the hashtable
%% Out: list of all currently mapped keys
%% -----------------------------------------------------------------------------
fetch_keys(H) ->
    .

unit_test() ->
    ok.