How do you link to packages during development?

[Sean Hess]

Pretty often while developing an application, I realize that some piece of it would be better as an external library published to Hackage. But I don't really know exactly what the interface will look like. I need a way to iterate the package while I'm developing my application, without needing to republish to hackage every time. 

How do you handle this workflow?

I'd like to put it in its own project folder on my local filesystem, with its own cabal and stack file. Then I want to have my application depend on it. When I make a change to the lib, I want to be able to reload it into my app quickly. 

I attempted to do this by adding the folder to the packages: setting, but it didn't work. See this stack overflow question for more info: http://stackoverflow.com/questions/40003225/stack-how-to-depend-on-a-package-during-development

[Dan Burton]

If only the one application is using it, then don't give it its own stack file, just move it into your project folder. Stack is well designed to handle "megarepos" with multiple packages under a single stack.yaml in this manner.

project/

  stack.yaml

  lib1/

    lib1.cabal

  app1/

    app1.cabal

Stack should also handle things the way you're trying to do it, but I personally have no experience doing it that way; perhaps someone else can advise on that scenario.

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-- Dan Burton

[Bryan Richter]

On Wed, Oct 12, 2016 at 09:24:41AM -0700, Sean Hess wrote:

> Pretty often while developing an application, I realize that some
> piece of it would be better as an external library published to
> Hackage. But I don't really know exactly what the interface will look
> like. I need a way to iterate the package while I'm developing my
> application, without needing to republish to hackage every time.
>
> How do you handle this workflow?

Stack is designed for this workflow. It looks like you've done
everything right (but note that including the stack.yaml in the library
is only strictly necessary for building it independently).

On SO you list the error as

Failed to load interface for ‘Network.Worker’

Does your library list that package under 'exposed-modules' in its Cabal
file?

[Sean Clark Hess]

@Dan, That will support my workflow, thank you, I'll give it a shot

@Bryan, Yes, it is listed. I think the "failed to load interface" error only happens because of the build/exit failure error. I don't really know what's going on with the build error. I looked at the log file and it didn't have any useful information in it. 

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[Sean Clark Hess]

Starting over made the problem magically disappear. I created a new folder in my project, slowly copied parts into it, and it worked right away. I moved this new folder out into a peer folder and exactly duplicated the structure that was failing before, and it is working. 

It must have been some cached build artifacts or something? I updated the lts resolver halfway through in my main project, maybe that threw it off. 

Thanks for all your help!