Are Erlang -callbacks to be invoked only through MFA functions (apply/3, spawn/3, …)? (Custom Behaviors HOWTO)
That's my suspicion as this simple code
-module(simple_server).
-export( [sayHello/0] ).
-callback say(Num :: term()) -> term().
sayHello() ->
io:fwrite( "Hello 1: ~pn", [ say(1) ]) ,
io:fwrite( "Hello 2: ~pn", [ say(2) ]) .
fails to be compiled:
$ erlc simple_server.erl
simple_server.erl:7: function say/1 undefined
simple_server.erl:8: function say/1 undefined
If that is the case, then this is not explicitly commented elsewhere:
official docs, "learn erlang", this answer.
callback erlang otp
asked Nov 14 '18 at 9:35
cibercitizen1cibercitizen1
12.2k135483
add a comment |
That's my suspicion as this simple code
-module(simple_server).
-export( [sayHello/0] ).
-callback say(Num :: term()) -> term().
sayHello() ->
io:fwrite( "Hello 1: ~pn", [ say(1) ]) ,
io:fwrite( "Hello 2: ~pn", [ say(2) ]) .
fails to be compiled:
$ erlc simple_server.erl
simple_server.erl:7: function say/1 undefined
simple_server.erl:8: function say/1 undefined
If that is the case, then this is not explicitly commented elsewhere:
official docs, "learn erlang", this answer.
callback erlang otp
asked Nov 14 '18 at 9:35
cibercitizen1cibercitizen1
12.2k135483
This question stackoverflow.com/questions/32336854/… exposes the same problem without clearly showing how callbacks are supposed to be called.
– cibercitizen1
Nov 14 '18 at 9:58
In the accepted answer, the callback function is called asCBM:fn(A).
– legoscia
Nov 14 '18 at 9:59
@legoscia Yes. Then, the name of the module implementing the callback must be supplied to the generic code.
– cibercitizen1
Nov 14 '18 at 10:02
@legoscia If you are sure about the ways a generic module can call a callback (to be provided in the future) you could write an answer here to be accepted. Thanks in advance.
– cibercitizen1
Nov 14 '18 at 10:06
add a comment |
That's my suspicion as this simple code
-module(simple_server).
-export( [sayHello/0] ).
-callback say(Num :: term()) -> term().
sayHello() ->
io:fwrite( "Hello 1: ~pn", [ say(1) ]) ,
io:fwrite( "Hello 2: ~pn", [ say(2) ]) .
fails to be compiled:
$ erlc simple_server.erl
simple_server.erl:7: function say/1 undefined
simple_server.erl:8: function say/1 undefined
If that is the case, then this is not explicitly commented elsewhere:
official docs, "learn erlang", this answer.
callback erlang otp
asked Nov 14 '18 at 9:35
cibercitizen1cibercitizen1
12.2k135483
That's my suspicion as this simple code
-module(simple_server).
-export( [sayHello/0] ).
-callback say(Num :: term()) -> term().
sayHello() ->
io:fwrite( "Hello 1: ~pn", [ say(1) ]) ,
io:fwrite( "Hello 2: ~pn", [ say(2) ]) .
fails to be compiled:
$ erlc simple_server.erl
simple_server.erl:7: function say/1 undefined
simple_server.erl:8: function say/1 undefined
If that is the case, then this is not explicitly commented elsewhere:
official docs, "learn erlang", this answer.
callback erlang otp
callback erlang otp
asked Nov 14 '18 at 9:35
cibercitizen1cibercitizen1
12.2k135483
asked Nov 14 '18 at 9:35
cibercitizen1cibercitizen1
12.2k135483
edited Nov 14 '18 at 12:01
cibercitizen1
asked Nov 14 '18 at 9:35
cibercitizen1cibercitizen1
12.2k135483
asked Nov 14 '18 at 9:35
cibercitizen1cibercitizen1
12.2k135483
asked Nov 14 '18 at 9:35
cibercitizen1cibercitizen1
12.2k135483
12.2k135483
This question stackoverflow.com/questions/32336854/… exposes the same problem without clearly showing how callbacks are supposed to be called.
– cibercitizen1
Nov 14 '18 at 9:58
In the accepted answer, the callback function is called asCBM:fn(A).
– legoscia
Nov 14 '18 at 9:59
@legoscia Yes. Then, the name of the module implementing the callback must be supplied to the generic code.
– cibercitizen1
Nov 14 '18 at 10:02
@legoscia If you are sure about the ways a generic module can call a callback (to be provided in the future) you could write an answer here to be accepted. Thanks in advance.
– cibercitizen1
Nov 14 '18 at 10:06
add a comment |
This question stackoverflow.com/questions/32336854/… exposes the same problem without clearly showing how callbacks are supposed to be called.
– cibercitizen1
Nov 14 '18 at 9:58
In the accepted answer, the callback function is called asCBM:fn(A).
– legoscia
Nov 14 '18 at 9:59
@legoscia Yes. Then, the name of the module implementing the callback must be supplied to the generic code.
– cibercitizen1
Nov 14 '18 at 10:02
@legoscia If you are sure about the ways a generic module can call a callback (to be provided in the future) you could write an answer here to be accepted. Thanks in advance.
– cibercitizen1
Nov 14 '18 at 10:06
This question stackoverflow.com/questions/32336854/… exposes the same problem without clearly showing how callbacks are supposed to be called.
– cibercitizen1
Nov 14 '18 at 9:58
This question stackoverflow.com/questions/32336854/… exposes the same problem without clearly showing how callbacks are supposed to be called.
– cibercitizen1
Nov 14 '18 at 9:58
In the accepted answer, the callback function is called as
CBM:fn(A).– legoscia
Nov 14 '18 at 9:59
In the accepted answer, the callback function is called as
CBM:fn(A).– legoscia
Nov 14 '18 at 9:59
@legoscia Yes. Then, the name of the module implementing the callback must be supplied to the generic code.
– cibercitizen1
Nov 14 '18 at 10:02
@legoscia Yes. Then, the name of the module implementing the callback must be supplied to the generic code.
– cibercitizen1
Nov 14 '18 at 10:02
@legoscia If you are sure about the ways a generic module can call a callback (to be provided in the future) you could write an answer here to be accepted. Thanks in advance.
– cibercitizen1
Nov 14 '18 at 10:06
@legoscia If you are sure about the ways a generic module can call a callback (to be provided in the future) you could write an answer here to be accepted. Thanks in advance.
– cibercitizen1
Nov 14 '18 at 10:06
add a comment |
2 Answers
2
active
oldest
votes
You need to provide the name of the callback module, which can be done through apply and spawn, but you can also make a simple call using a variable as the module name, e.g. CallbackModule:say(1).
So you could do either:
sayHello(CallbackModule) ->
io:fwrite( "Hello 1: ~pn", [ CallbackModule:say(1) ]) ,
io:fwrite( "Hello 2: ~pn", [ CallbackModule:say(2) ]) .
or
sayHello(CallbackModule) ->
io:fwrite( "Hello 1: ~pn", [ apply(CallbackModule, say, [1]) ]) ,
io:fwrite( "Hello 2: ~pn", [ apply(CallbackModule, say, [2]) ]) .
Those two versions are equivalent.
Let's create a callback module implementing the simple_server behaviour:
-module(my_callback).
-behaviour(simple_server).
-export([say/1]).
say(N) ->
N, is, the, loneliest, number.
Now we can call simple_server:sayHello with the module name as the argument:
> simple_server:sayHello(my_callback).
Hello 1: 1,is,the,loneliest,number
Hello 2: 2,is,the,loneliest,number
answered Nov 14 '18 at 11:14
legoscialegoscia
28.9k1181111
1
Thanks a lot! I've also prepared a simple explanatory example, including compile orders, which are very important (-pa flag).
– cibercitizen1
Nov 14 '18 at 11:30
add a comment |
HOWTO Erlang Custom Behaviors (template method pattern).
-1. Write a generic module. Here, an algorithm is defined, but some steps (callback functions in Erlang nomenclature) are left for a future specific definition.
%% generic.erl
-module(generic).
-export( [sayHello/1] ).
-callback say(Num :: term()) -> term(). %% future definition
%% generic algorithm: needs the reference to the provider module
sayHello(ProviderModule) ->
io:fwrite( "Hello 1: ~pn", [ ProviderModule:say(1) ]) ,
io:fwrite( "Hello 2: ~pn", [ ProviderModule:say(2) ]) .
-2. Compile generic.erl
erlc generic.erl
-(3.) Try to write a provider (callback) module
%% callbacks1.erl (fails to implement say/1 callback)
-module( callbacks1 ).
-behaviour( generic ).
-(4.) Compile callbacks1.erl: use -pa . to say where generic.beam is. (Therefore, the expected warning about say/1 is issued).
erlc -pa . callbacks1.erl
callbacks1.erl:2: Warning: undefined callback function say/1 (behaviour 'generic')
(Note: If -pa is not given, you'll got this: "callbacks1.erl:2: Warning: behaviour generic undefined")
-3. Write a correct provider (callback) module.
%% callbacks2.erl
-module( callbacks2 ).
-behaviour( generic ).
-export( [say/1] ).
say(1) -> "good morning";
say(2) -> "bon jour";
say(_) -> "hi".
-4. Compile it
erlc -pa . callbacks2.erl
(Ok now).
-5. Write a main.erl to gather generic module with callback module.
%% main.erl
-module( main ).
-export( [main/0] ).
main() ->
%% call the generic algorithm telling it what callback module to use
generic:sayHello( callbacks2 )
. % ()
-6. Compile and run main
erlc main.erl
erl -noshell -s main main -s init stop
We get:
Hello 1: "good morning"
Hello 2: "bon jour"
answered Nov 14 '18 at 11:52
cibercitizen1cibercitizen1
12.2k135483
add a comment |
Your Answer
StackExchange.ifUsing("editor", function ()
StackExchange.using("externalEditor", function ()
StackExchange.using("snippets", function ()
StackExchange.snippets.init();
);
);
, "code-snippets");
StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "1"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);
else
createEditor();
);
function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader:
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
,
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);
);
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53296965%2fare-erlang-callbacks-to-be-invoked-only-through-mfa-functions-apply-3-spawn-3%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
You need to provide the name of the callback module, which can be done through apply and spawn, but you can also make a simple call using a variable as the module name, e.g. CallbackModule:say(1).
So you could do either:
sayHello(CallbackModule) ->
io:fwrite( "Hello 1: ~pn", [ CallbackModule:say(1) ]) ,
io:fwrite( "Hello 2: ~pn", [ CallbackModule:say(2) ]) .
or
sayHello(CallbackModule) ->
io:fwrite( "Hello 1: ~pn", [ apply(CallbackModule, say, [1]) ]) ,
io:fwrite( "Hello 2: ~pn", [ apply(CallbackModule, say, [2]) ]) .
Those two versions are equivalent.
Let's create a callback module implementing the simple_server behaviour:
-module(my_callback).
-behaviour(simple_server).
-export([say/1]).
say(N) ->
N, is, the, loneliest, number.
Now we can call simple_server:sayHello with the module name as the argument:
> simple_server:sayHello(my_callback).
Hello 1: 1,is,the,loneliest,number
Hello 2: 2,is,the,loneliest,number
answered Nov 14 '18 at 11:14
legoscialegoscia
28.9k1181111
1
Thanks a lot! I've also prepared a simple explanatory example, including compile orders, which are very important (-pa flag).
– cibercitizen1
Nov 14 '18 at 11:30
add a comment |
You need to provide the name of the callback module, which can be done through apply and spawn, but you can also make a simple call using a variable as the module name, e.g. CallbackModule:say(1).
So you could do either:
sayHello(CallbackModule) ->
io:fwrite( "Hello 1: ~pn", [ CallbackModule:say(1) ]) ,
io:fwrite( "Hello 2: ~pn", [ CallbackModule:say(2) ]) .
or
sayHello(CallbackModule) ->
io:fwrite( "Hello 1: ~pn", [ apply(CallbackModule, say, [1]) ]) ,
io:fwrite( "Hello 2: ~pn", [ apply(CallbackModule, say, [2]) ]) .
Those two versions are equivalent.
Let's create a callback module implementing the simple_server behaviour:
-module(my_callback).
-behaviour(simple_server).
-export([say/1]).
say(N) ->
N, is, the, loneliest, number.
Now we can call simple_server:sayHello with the module name as the argument:
> simple_server:sayHello(my_callback).
Hello 1: 1,is,the,loneliest,number
Hello 2: 2,is,the,loneliest,number
answered Nov 14 '18 at 11:14
legoscialegoscia
28.9k1181111
1
Thanks a lot! I've also prepared a simple explanatory example, including compile orders, which are very important (-pa flag).
– cibercitizen1
Nov 14 '18 at 11:30
add a comment |
You need to provide the name of the callback module, which can be done through apply and spawn, but you can also make a simple call using a variable as the module name, e.g. CallbackModule:say(1).
So you could do either:
sayHello(CallbackModule) ->
io:fwrite( "Hello 1: ~pn", [ CallbackModule:say(1) ]) ,
io:fwrite( "Hello 2: ~pn", [ CallbackModule:say(2) ]) .
or
sayHello(CallbackModule) ->
io:fwrite( "Hello 1: ~pn", [ apply(CallbackModule, say, [1]) ]) ,
io:fwrite( "Hello 2: ~pn", [ apply(CallbackModule, say, [2]) ]) .
Those two versions are equivalent.
Let's create a callback module implementing the simple_server behaviour:
-module(my_callback).
-behaviour(simple_server).
-export([say/1]).
say(N) ->
N, is, the, loneliest, number.
Now we can call simple_server:sayHello with the module name as the argument:
> simple_server:sayHello(my_callback).
Hello 1: 1,is,the,loneliest,number
Hello 2: 2,is,the,loneliest,number
answered Nov 14 '18 at 11:14
legoscialegoscia
28.9k1181111
You need to provide the name of the callback module, which can be done through apply and spawn, but you can also make a simple call using a variable as the module name, e.g. CallbackModule:say(1).
So you could do either:
sayHello(CallbackModule) ->
io:fwrite( "Hello 1: ~pn", [ CallbackModule:say(1) ]) ,
io:fwrite( "Hello 2: ~pn", [ CallbackModule:say(2) ]) .
or
sayHello(CallbackModule) ->
io:fwrite( "Hello 1: ~pn", [ apply(CallbackModule, say, [1]) ]) ,
io:fwrite( "Hello 2: ~pn", [ apply(CallbackModule, say, [2]) ]) .
Those two versions are equivalent.
Let's create a callback module implementing the simple_server behaviour:
-module(my_callback).
-behaviour(simple_server).
-export([say/1]).
say(N) ->
N, is, the, loneliest, number.
Now we can call simple_server:sayHello with the module name as the argument:
> simple_server:sayHello(my_callback).
Hello 1: 1,is,the,loneliest,number
Hello 2: 2,is,the,loneliest,number
answered Nov 14 '18 at 11:14
legoscialegoscia
28.9k1181111
answered Nov 14 '18 at 11:14
legoscialegoscia
28.9k1181111
answered Nov 14 '18 at 11:14
legoscialegoscia
28.9k1181111
answered Nov 14 '18 at 11:14
legoscialegoscia
28.9k1181111
28.9k1181111
1
Thanks a lot! I've also prepared a simple explanatory example, including compile orders, which are very important (-pa flag).
– cibercitizen1
Nov 14 '18 at 11:30
add a comment |
1
Thanks a lot! I've also prepared a simple explanatory example, including compile orders, which are very important (-pa flag).
– cibercitizen1
Nov 14 '18 at 11:30
1
1
Thanks a lot! I've also prepared a simple explanatory example, including compile orders, which are very important (-pa flag).
– cibercitizen1
Nov 14 '18 at 11:30
Thanks a lot! I've also prepared a simple explanatory example, including compile orders, which are very important (-pa flag).
– cibercitizen1
Nov 14 '18 at 11:30
add a comment |
HOWTO Erlang Custom Behaviors (template method pattern).
-1. Write a generic module. Here, an algorithm is defined, but some steps (callback functions in Erlang nomenclature) are left for a future specific definition.
%% generic.erl
-module(generic).
-export( [sayHello/1] ).
-callback say(Num :: term()) -> term(). %% future definition
%% generic algorithm: needs the reference to the provider module
sayHello(ProviderModule) ->
io:fwrite( "Hello 1: ~pn", [ ProviderModule:say(1) ]) ,
io:fwrite( "Hello 2: ~pn", [ ProviderModule:say(2) ]) .
-2. Compile generic.erl
erlc generic.erl
-(3.) Try to write a provider (callback) module
%% callbacks1.erl (fails to implement say/1 callback)
-module( callbacks1 ).
-behaviour( generic ).
-(4.) Compile callbacks1.erl: use -pa . to say where generic.beam is. (Therefore, the expected warning about say/1 is issued).
erlc -pa . callbacks1.erl
callbacks1.erl:2: Warning: undefined callback function say/1 (behaviour 'generic')
(Note: If -pa is not given, you'll got this: "callbacks1.erl:2: Warning: behaviour generic undefined")
-3. Write a correct provider (callback) module.
%% callbacks2.erl
-module( callbacks2 ).
-behaviour( generic ).
-export( [say/1] ).
say(1) -> "good morning";
say(2) -> "bon jour";
say(_) -> "hi".
-4. Compile it
erlc -pa . callbacks2.erl
(Ok now).
-5. Write a main.erl to gather generic module with callback module.
%% main.erl
-module( main ).
-export( [main/0] ).
main() ->
%% call the generic algorithm telling it what callback module to use
generic:sayHello( callbacks2 )
. % ()
-6. Compile and run main
erlc main.erl
erl -noshell -s main main -s init stop
We get:
Hello 1: "good morning"
Hello 2: "bon jour"
answered Nov 14 '18 at 11:52
cibercitizen1cibercitizen1
12.2k135483
add a comment |
HOWTO Erlang Custom Behaviors (template method pattern).
-1. Write a generic module. Here, an algorithm is defined, but some steps (callback functions in Erlang nomenclature) are left for a future specific definition.
%% generic.erl
-module(generic).
-export( [sayHello/1] ).
-callback say(Num :: term()) -> term(). %% future definition
%% generic algorithm: needs the reference to the provider module
sayHello(ProviderModule) ->
io:fwrite( "Hello 1: ~pn", [ ProviderModule:say(1) ]) ,
io:fwrite( "Hello 2: ~pn", [ ProviderModule:say(2) ]) .
-2. Compile generic.erl
erlc generic.erl
-(3.) Try to write a provider (callback) module
%% callbacks1.erl (fails to implement say/1 callback)
-module( callbacks1 ).
-behaviour( generic ).
-(4.) Compile callbacks1.erl: use -pa . to say where generic.beam is. (Therefore, the expected warning about say/1 is issued).
erlc -pa . callbacks1.erl
callbacks1.erl:2: Warning: undefined callback function say/1 (behaviour 'generic')
(Note: If -pa is not given, you'll got this: "callbacks1.erl:2: Warning: behaviour generic undefined")
-3. Write a correct provider (callback) module.
%% callbacks2.erl
-module( callbacks2 ).
-behaviour( generic ).
-export( [say/1] ).
say(1) -> "good morning";
say(2) -> "bon jour";
say(_) -> "hi".
-4. Compile it
erlc -pa . callbacks2.erl
(Ok now).
-5. Write a main.erl to gather generic module with callback module.
%% main.erl
-module( main ).
-export( [main/0] ).
main() ->
%% call the generic algorithm telling it what callback module to use
generic:sayHello( callbacks2 )
. % ()
-6. Compile and run main
erlc main.erl
erl -noshell -s main main -s init stop
We get:
Hello 1: "good morning"
Hello 2: "bon jour"
answered Nov 14 '18 at 11:52
cibercitizen1cibercitizen1
12.2k135483
add a comment |
HOWTO Erlang Custom Behaviors (template method pattern).
-1. Write a generic module. Here, an algorithm is defined, but some steps (callback functions in Erlang nomenclature) are left for a future specific definition.
%% generic.erl
-module(generic).
-export( [sayHello/1] ).
-callback say(Num :: term()) -> term(). %% future definition
%% generic algorithm: needs the reference to the provider module
sayHello(ProviderModule) ->
io:fwrite( "Hello 1: ~pn", [ ProviderModule:say(1) ]) ,
io:fwrite( "Hello 2: ~pn", [ ProviderModule:say(2) ]) .
-2. Compile generic.erl
erlc generic.erl
-(3.) Try to write a provider (callback) module
%% callbacks1.erl (fails to implement say/1 callback)
-module( callbacks1 ).
-behaviour( generic ).
-(4.) Compile callbacks1.erl: use -pa . to say where generic.beam is. (Therefore, the expected warning about say/1 is issued).
erlc -pa . callbacks1.erl
callbacks1.erl:2: Warning: undefined callback function say/1 (behaviour 'generic')
(Note: If -pa is not given, you'll got this: "callbacks1.erl:2: Warning: behaviour generic undefined")
-3. Write a correct provider (callback) module.
%% callbacks2.erl
-module( callbacks2 ).
-behaviour( generic ).
-export( [say/1] ).
say(1) -> "good morning";
say(2) -> "bon jour";
say(_) -> "hi".
-4. Compile it
erlc -pa . callbacks2.erl
(Ok now).
-5. Write a main.erl to gather generic module with callback module.
%% main.erl
-module( main ).
-export( [main/0] ).
main() ->
%% call the generic algorithm telling it what callback module to use
generic:sayHello( callbacks2 )
. % ()
-6. Compile and run main
erlc main.erl
erl -noshell -s main main -s init stop
We get:
Hello 1: "good morning"
Hello 2: "bon jour"
answered Nov 14 '18 at 11:52
cibercitizen1cibercitizen1
12.2k135483
HOWTO Erlang Custom Behaviors (template method pattern).
-1. Write a generic module. Here, an algorithm is defined, but some steps (callback functions in Erlang nomenclature) are left for a future specific definition.
%% generic.erl
-module(generic).
-export( [sayHello/1] ).
-callback say(Num :: term()) -> term(). %% future definition
%% generic algorithm: needs the reference to the provider module
sayHello(ProviderModule) ->
io:fwrite( "Hello 1: ~pn", [ ProviderModule:say(1) ]) ,
io:fwrite( "Hello 2: ~pn", [ ProviderModule:say(2) ]) .
-2. Compile generic.erl
erlc generic.erl
-(3.) Try to write a provider (callback) module
%% callbacks1.erl (fails to implement say/1 callback)
-module( callbacks1 ).
-behaviour( generic ).
-(4.) Compile callbacks1.erl: use -pa . to say where generic.beam is. (Therefore, the expected warning about say/1 is issued).
erlc -pa . callbacks1.erl
callbacks1.erl:2: Warning: undefined callback function say/1 (behaviour 'generic')
(Note: If -pa is not given, you'll got this: "callbacks1.erl:2: Warning: behaviour generic undefined")
-3. Write a correct provider (callback) module.
%% callbacks2.erl
-module( callbacks2 ).
-behaviour( generic ).
-export( [say/1] ).
say(1) -> "good morning";
say(2) -> "bon jour";
say(_) -> "hi".
-4. Compile it
erlc -pa . callbacks2.erl
(Ok now).
-5. Write a main.erl to gather generic module with callback module.
%% main.erl
-module( main ).
-export( [main/0] ).
main() ->
%% call the generic algorithm telling it what callback module to use
generic:sayHello( callbacks2 )
. % ()
-6. Compile and run main
erlc main.erl
erl -noshell -s main main -s init stop
We get:
Hello 1: "good morning"
Hello 2: "bon jour"
answered Nov 14 '18 at 11:52
cibercitizen1cibercitizen1
12.2k135483
edited Nov 14 '18 at 13:29
answered Nov 14 '18 at 11:52
cibercitizen1cibercitizen1
12.2k135483
answered Nov 14 '18 at 11:52
cibercitizen1cibercitizen1
12.2k135483
answered Nov 14 '18 at 11:52
cibercitizen1cibercitizen1
12.2k135483
12.2k135483
add a comment |
add a comment |
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53296965%2fare-erlang-callbacks-to-be-invoked-only-through-mfa-functions-apply-3-spawn-3%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
This question stackoverflow.com/questions/32336854/… exposes the same problem without clearly showing how callbacks are supposed to be called.
– cibercitizen1
Nov 14 '18 at 9:58
In the accepted answer, the callback function is called as
CBM:fn(A).– legoscia
Nov 14 '18 at 9:59
@legoscia Yes. Then, the name of the module implementing the callback must be supplied to the generic code.
– cibercitizen1
Nov 14 '18 at 10:02
@legoscia If you are sure about the ways a generic module can call a callback (to be provided in the future) you could write an answer here to be accepted. Thanks in advance.
– cibercitizen1
Nov 14 '18 at 10:06