Modules cannot have ports with same name

[b123400]

Elm version: 0.17.0

I have two modules, they both have a port with the same name:

port module ModuleA exposing (main)

import Html exposing (text)
import Platform.Sub as Sub

port incomePort : (String -> msg) -> Sub msg

main =
  text "Hello"

port module ModuleB exposing (main)

import Html exposing (text)
import Platform.Sub as Sub

port incomePort : (String -> msg) -> Sub msg

main =
  text "Hey!"

And I compiled it by this command:

elm make ModuleA.elm ModuleB.elm --output combined.js

The generated JS file will output the following error:

Error: There can only be one port named `incomePort`, but your program has multiple.

These two modules are not connected and there should be no ambiguity between the ports. I think the ports name checking should be bounded to the module, instead of JS-file-wise.

By the way, when I generate the modules separately and include them in the same page, there is no error.

elm make ModuleA.elm --output a.js
elm make ModuleB.elm --output b.js

<script type="text/javascript" src="a.js"></script>
<script type="text/javascript" src="b.js"></script>

Is this behaviour intended? I can try to send a PR to fix it if it is not :)

[process-bot]

Thanks for the issue! Make sure it satisfies this checklist. My human colleagues will appreciate it!

Here is what to expect next, and if anyone wants to comment, keep these things in mind.

[process-bot]

Thanks for the issue! Make sure it satisfies this checklist. My human colleagues will appreciate it!

Here is what to expect next, and if anyone wants to comment, keep these things in mind.

[sachin-bs]

bump, any updates?

[sachin-bs]

bump, any updates?

[kachkaev]

Just raised a similar concern on stackoverflow. Being a newcomer in Elm, here is what I wanted to do to avoid import glitches:

import MyModule exposing (myFunction as myRenamedFunction, somethingElse)

Having that supported by the compiler would be awesome!

[kachkaev]

Just raised a similar concern on stackoverflow. Being a newcomer in Elm, here is what I wanted to do to avoid import glitches:

import MyModule exposing (myFunction as myRenamedFunction, somethingElse)

Having that supported by the compiler would be awesome!

[rgrempel]

These two modules are not connected and there should be no ambiguity between the ports.

But think about the way you use the ports, on the Javascript side. You'll end up saying stuff like:

var elmApp = Elm.Main.fullscreen({
   ...
});

elmApp.ports.cacheCredentials.subscribe(function(params) {
   ...
}

Now, which cacheCredentials does this refer to, if the port name is used in two different modules?

Of course, there would be a way to solve this problem -- you could imagine elmApp.ports exposing a port name qualified by the module name, for instance -- I just wanted to point out that it's not a trivial problem to fix. Or, in other words, there is currently an ambiguity, even if you could imagine deeper changes that might avoid it.

[rgrempel]

These two modules are not connected and there should be no ambiguity between the ports.

But think about the way you use the ports, on the Javascript side. You'll end up saying stuff like:

var elmApp = Elm.Main.fullscreen({
   ...
});

elmApp.ports.cacheCredentials.subscribe(function(params) {
   ...
}

Now, which cacheCredentials does this refer to, if the port name is used in two different modules?

Of course, there would be a way to solve this problem -- you could imagine elmApp.ports exposing a port name qualified by the module name, for instance -- I just wanted to point out that it's not a trivial problem to fix. Or, in other words, there is currently an ambiguity, even if you could imagine deeper changes that might avoid it.

[fdbeirao]

I just want to post here that this talk "The Importance of Ports" by Murphy Randle has helped me (YMMV) a lot when using ports in my Elm apps. I now have one single Ports.elm module, which is the only port module and which contains two ports: infoForOutside and infoForElm. This mitigates/works around the ambiguity raised in this issue.

[fdbeirao]

I just want to post here that this talk "The Importance of Ports" by Murphy Randle has helped me (YMMV) a lot when using ports in my Elm apps. I now have one single Ports.elm module, which is the only port module and which contains two ports: infoForOutside and infoForElm. This mitigates/works around the ambiguity raised in this issue.