erlang模块的模块信息中未更新MD5

Question

FYI: I just started to learn Erlang with the help of https://learnyousomeerlang.com .

While going through the chapters I encountered about module_info. The following is the output that I got for one of the module.

[{module,useless},
 {exports,[{add,2},
           {hello,0},
           {greet_and_add_two,1},
           {module_info,0},
           {module_info,1}]},
 {attributes,[{vsn,[296174539721071843666185210011547328263]},
              {author,"An Erlang Champ"}]},
 {compile,[{version,"7.4"},
           {options,[debug_info,export_all]},
           {source,"/Users/vivekdhayalan/useless.erl"}]},
 {native,false},
 {md5,<<222,209,36,56,31,223,59,231,71,237,66,109,149,39,
        223,7>>}]

I have noticed md5 attribute in my output on curious I updated my module and checked the module info after compiling by module once again. But, I still found the same md5 thinking what could be the reason.

If you have any clues please help to understand. Might, be I'm to curious about md5 as I'm yet complete the chapter.

note: vsn is also not getting updated

Updating with more info.

My initial code:

-module(useless).
-export([add/2, hello/0, greet_and_add_two/1]).

add(C,B) ->
C + B.

%% Shows greetings.
%% io:format/1 is the standard function used to output text.
hello() ->
io:format("Hello, world!~n").

greet_and_add_two(X) ->
hello(),
add(X,2).

Module info & compile steps

28> compile:file(useless, [debug_info, export_all]).
{ok,useless}
29> useless:module_info().                          
[{module,useless},
 {exports,[{add,2},
           {hello,0},
           {greet_and_add_two,1},
           {module_info,0},
           {module_info,1}]},
 {attributes,[{vsn,[296174539721071843666185210011547328263]},
              {author,"An Erlang Champ"}]},
 {compile,[{version,"7.4"},
           {options,[debug_info,export_all]},
           {source,"/Users/vivekdhayalan/useless.erl"}]},
 {native,false},
 {md5,<<222,209,36,56,31,223,59,231,71,237,66,109,149,39,
        223,7>>}]

I'm updating my module just with adding author as below

-module(useless).
-export([add/2, hello/0, greet_and_add_two/1]).
-author("An Erlang Champ").

add(C,B) ->
C + B.

%% Shows greetings.
%% io:format/1 is the standard function used to output text.
hello() ->
io:format("Hello, world!~n").

greet_and_add_two(X) ->
hello(),
add(X,2).

my module info after compile.

compile:file(useless, [debug_info, export_all]).
{ok,useless}
31> useless:module_info().                          
[{module,useless},
 {exports,[{add,2},
           {hello,0},
           {greet_and_add_two,1},
           {module_info,0},
           {module_info,1}]},
 {attributes,[{vsn,[296174539721071843666185210011547328263]},
              {author,"An Erlang Champ"}]},
 {compile,[{version,"7.4"},
           {options,[debug_info,export_all]},
           {source,"/Users/vivekdhayalan/useless.erl"}]},
 {native,false},
 {md5,<<222,209,36,56,31,223,59,231,71,237,66,109,149,39,
        223,7>>}]

As we could see the md5 has not updated even after adding info.

Answer 1

compile:file() compiles to a new .beam file on disk, but does not load it. The module_info() function reports the status of the loaded version. The shell c() shortcut will both compile and load - use that instead for interactive work.

Answer 2

-module(my).
-compile([export_all]).

go() -> "hello".

In the shell:

~/erlang_programs$ erl
Erlang/OTP 20 [erts-9.3] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:10] [hipe] [kernel-poll:false]
Eshell V9.3  (abort with ^G)

1> c(my).
my.erl:2: Warning: export_all flag enabled - all functions will be exported
{ok,my}

2> my:module_info().
[{module,my},
 {exports,[{go,0},{module_info,0},{module_info,1}]},
 {attributes,[{vsn,[317460282063015155415500557234702055363]}]},
 {compile,[{options,[]},
           {version,"7.1.5"},
           {source,"/Users/7stud/erlang_programs/my.erl"}]},
 {native,false},
 {md5,<<"îÔ W­ÝÒ\n©¥ëíQ&÷Ã">>}]

Adding another function:

-module(my).
-compile([export_all]).

stop() -> "goodbye".
go() -> "hello".

In the shell:

5> c(my).           
my.erl:2: Warning: export_all flag enabled - all functions will be exported
{ok,my}

6> my:module_info().
[{module,my},
 {exports,[{stop,0},
           {go,0},
           {module_info,0},
           {module_info,1}]},
 {attributes,[{vsn,[210928589040636765166954307796272702313]}]},
 {compile,[{options,[]},
           {version,"7.1.5"},
           {source,"/Users/7stud/erlang_programs/my.erl"}]},
 {native,false}, 
 {md5,<<158,175,94,91,0,91,194,106,194,244,45,224,190,48,
        99,105>>}]

I updated my module and checked the module info after compiling by module once again. But, I still found the same md5 thinking what could be the reason.

Prove it.