immutable means immutable

gistfile1.erl

Gotcha with Erlang

➜  v-kserl-v-02-code  erl
Erlang R16B03-1 (erts-5.10.4) [source] [64-bit] [smp:4:4] [async-threads:10] [hipe] [kernel-poll:false] [dtrace]

Eshell V5.10.4  (abort with ^G)
1> VALUE = fun() -> io:format("I have value!~n") end.
#Fun<erl_eval.20.80484245>
2> K = mykey.
mykey
3> D1 = dict:new().
{dict,0,16,16,8,80,48,
      {[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],[]},
      {{[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],[]}}}
4> dict:store(K, VALUE, D1).
{dict,1,16,16,8,80,48,
      {[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],[]},
      {{[],[],[],[],[],[],[],[],[],
        [[mykey|#Fun<erl_eval.20.80484245>]],
        [],[],[],[],[],[]}}}
5> D1.
{dict,0,16,16,8,80,48,
      {[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],[]},
      {{[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],[]}}}
6> dict:fetch(K, D1).
** exception error: bad argument
     in function  dict:fetch/2
        called as dict:fetch(mykey,
                             {dict,0,16,16,8,80,48,
                                   {[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],
                                    []},
                                   {{[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],
                                     []}}})
7> D2 = dict:store(K, VALUE, D1).
{dict,1,16,16,8,80,48,
      {[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],[]},
      {{[],[],[],[],[],[],[],[],[],
        [[mykey|#Fun<erl_eval.20.80484245>]],
        [],[],[],[],[],[]}}}
8> dict:fetch(K, D2).
#Fun<erl_eval.20.80484245>
9>
[erlang] 0:..erl-v-02-code*                                                                                                      "Jamess-MacBook-Air.loc" 21:48 20-Jun-14