Used in http://stackoverflow.com/questions/16815317/erlang-binary-will-this-result-in-a-copy call with spawn(test, bla, []).

copy.erl

-module(test).
-export([foo/2, bla/0]).

%% here we prepend and append, resulting in a copy

bla() ->
    io:format("before: ~p~n", [erlang:process_info(self(),binary)]),
    A = foo(<<"12345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578123457812345781234578">>, <<"append after me">>),
    io:format("after: ~p~n", [erlang:process_info(self(),binary)]),
    A.

foo(<<>>, A) ->
    A;
foo(<<X:1/binary, R/binary>>, A) ->
    I = binary_to_integer(X),
    foo(R, <<I, A/binary, I>>).

no_copy.erl

-module(test).
-export([foo/2, bla/0]).

%% here we append, binary is not copied

bla() ->
    io:format("before: ~p~n", [erlang:process_info(self(),binary)]),
    A = foo(<<"1234578">>, <<"append after me">>),
    io:format("after: ~p~n", [erlang:process_info(self(),binary)]).

foo(<<>>, A) ->
    A;
foo(<<X:1/binary, R/binary>>, A) ->
    I = binary_to_integer(X),
    foo(R, <<A/binary, I>>).

My output of copy.erl:

70> spawn(copy, bla, []).
before: {binary,[]}
after: {binary,[{25930408,256,1}]}
<0.23197.0>

My output of no_copy.erl:

76> spawn(no_copy, bla, []).
before: {binary,[]}
after: {binary,[{44537112,1801,1},
{25569608,1803,1},
{25571440,1805,1},
{25573272,1807,1}]}
<0.14673.5>

BinInfo is a list containing miscellaneous information about binaries currently being referred to by this process.
So, how can you figure out the code is optimized or not ?