src/hope_kv_list.erl

   1 %%%----------------------------------------------------------------------------
   2 %%% Equivalent to stdlib's orddict, but with a pretty (IMO), uniform interface.
   3 %%%----------------------------------------------------------------------------
   4 -module(hope_kv_list).
   5
   6 -behavior(hope_dictionary).
   7
   8 -export_type(
   9     [ t/2
  10     ]).
  11
  12 -export(
  13     [ empty/0
  14     , get/2
  15     , set/3
  16     , update/3
  17     , iter/2
  18     , map/2
  19     , filter/2
  20     , fold/3
  21     , of_kv_list/1
  22     , to_kv_list/1
  23     ]).
  24
  25
  26 -type t(K, V) ::
  27     [{K, V}].
  28
  29
  30 %% ============================================================================
  31 %% API
  32 %% ============================================================================
  33
  34 -spec empty() ->
  35     [].
  36 empty() ->
  37     [].
  38
  39 get(T, K) ->
  40     case lists:keyfind(K, 1, T)
  41     of  false  -> none
  42     ;   {K, V} -> {some, V}
  43     end.
  44
  45 set(T, K, V) ->
  46     lists:keystore(K, 1, T, {K, V}).
  47
  48 update(T, K, F) ->
  49     V1Opt = get(T, K),
  50     V2 = F(V1Opt),
  51     % TODO: Eliminate the 2nd lookup.
  52     set(T, K, V2).
  53
  54 iter(T, F1) ->
  55     F2 = lift_map(F1),
  56     lists:foreach(F2, T).
  57
  58 map(T, F1) ->
  59     F2 = fun ({K, _}=X) -> {K, apply_map(F1, X)} end,
  60     lists:map(F2, T).
  61
  62 filter(T, F1) ->
  63     F2 = lift_map(F1),
  64     lists:filter(F2, T).
  65
  66 fold(T, F1, Accumulator) ->
  67     F2 = fun ({K, V}, Acc) -> F1(K, V, Acc) end,
  68     lists:foldl(F2, T, Accumulator).
  69
  70 to_kv_list(T) ->
  71     T.
  72
  73 of_kv_list(List) ->
  74     % TODO: Decide if validation is to be done here. Do so if yes.
  75     List.
  76
  77
  78 %% ============================================================================
  79 %% Helpers
  80 %% ============================================================================
  81
  82 lift_map(F) ->
  83     fun (X) -> apply_map(F, X) end.
  84
  85 apply_map(F, {K, V}) ->
  86     F(K, V).