filtering dict like a boss.

dict_filter.erl

-module(main).
-export([start/0]).
-import(io, [fwrite/2]).

%% internal callback when calling
%% dict:filter/2
filter_even(_, Value) ->
  case lists:nth(1, Value) rem 2 of
    0 -> true;
    1 -> false
  end.

debug(Value) -> fwrite("~p~n", [Value]).

start() ->
  D0 = dict:append("1", 1, dict:new()),
  D1 = dict:append("2", 2, D0),
  D2 = dict:append("3", 3, D1),
  D3 = dict:append("4", 4, D2),
  D4 = dict:append("5", 5, D3),
  debug(dict:fetch("1", D4)),
  debug(dict:fetch("2", D4)),
  debug(dict:fetch("3", D4)),
  debug(dict:fetch("4", D4)),
  debug(dict:fetch("5", D4)),
  D5 = dict:filter(fun filter_even/2, D4),
  debug(dict:fetch("2", D5)),
  debug(dict:fetch("4", D5)).