I am testing hint library which does magic thing - evaluates Haskell code in runtime! The library is working almost as expected, but following deviation raised a question in my head.
Let's say there is a typical new stack project from a template with app and library. Dependence of app on library is described same way as any other package (base, text, lens, etc), but Haskell script file cannot import modules residing in the library of the same stack package, meanwhile modules from hackage libraries such as process library are resolved without any issue for the script.
Module required inside a script becomes available once I extract it into a stack sub packages.
So, is there a linking trick voiding extra stack sub package?
link the issue on Github
Try running stack install to install your package into the package database.
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I found myself writing Haskell commands based upon other commands provided by other Haskell packages, but i could not find a way to install an executable as a dependency.
As far as i could see, Cabal and Stack provide ways for a package to depend on a library, but not on an executable.
If i want to build upon the functionality already provided by another executable, the only way i know is to ask the users to install that other package as well. That also means that i cannot assume the executable is there or its version is the right one.
So is there a way for an Haskell package to depend on an executable provided by another package?
I'm trying to write a small web application fully in Haskell. I have 3 logical packages:
A backend, using servant
A frontend, using reflex, reflex-dom and servant-reflex
A shared package defining the Servant API for communication between the 2 and some data types for that API to use.
That last package is giving me trouble. I don't know how to structure the project so the other 2 packages can use it. I see 2 options at the moment:
Each package has its own stack file and git repository. Import the shared package using an extra-deps git link. The problem with this approach is it means I have to push any change to the shared package to GitHub before I can test it out with the other packages. Also I'd have to build everything separately.
Use a single repository with a single stack.yml file. I'd prefer this, since it keeps everything together and also assures all packages are using the same resolver. In this case I would list all the packages in the packages: option. However, the client needs to be compiled with GHCJS, not GHC, and I don't see an option in the documentation to override the compiler for 1 specific package.
Is there a way to make option 2 work? Or is there a better way to do this?
The recommended approach is to have two stack project files (e.g. stack-frontend.yaml using GHCJS and stack-backend.yaml using GHC), and then use the --stack-yaml argument to switch between them (e.g. use stack --stack-yaml=stack-frontend.yaml build to build the frontend, and stack --stack-yaml=stack-backend.yaml build to build the backend). Both stack-*.yaml files can include the shared servant API.
I understand that packages hold several modules, but I'm starting to get confused as to if packages and modules are dependencies. Also, libraries to me maybe seem like packages you install via NPM, Nuget, RubyGems, Bower, Homebrew, or Chocolatey. So are libraries packages? Dependencies are something you need to load within your application, to have a certain functionality, but aren't some libraries(jQuery) seen as a dependency? So yea, what are the differences between these concepts?
Libraries are just a bunch of code anyone can use. For example, React.js is a JavaScript library for building front end components.
If I decide to use this library in my app, then React will become one of the modules (aka an installed instance of the library) that my app depends on. So dependencies are pretty much all of the libraries your app depends on, in order to run the way you expect it to run.
I asked the same question you did about dependencies, and I learned that it's a matter of understanding how these terms relate to one another rather than finding isolated definitions for each of them.
Hope this helps!
Basically a package is a pack with some features which fullfills some functionality of your app.
Once you install any package using npm then the package is installed as a dependency in your app inside your package.json file along with its modules(aka libraries consist of classes) stored inside node_modules folder.
I hope its clear now.
I have a locally authored Haskell project, which produces both:
a binary executable, and
several new Haskell modules, which I'd like made accessible to my other, Haskell based, executables.
After:
stack build
stack install
I'm finding that:
the binary executable (#1, above) runs just fine from any directory.
But, the new Haskell modules (#2, above) are only found when I'm running from within my project directory! (That is, for any executable other than #1, above.)
I need to be able to find the new modules from anywhere.
How can I achieve this?
Each stack project is in its own sandbox, so the compiled modules can only be used within that project. Compiled dependencies (which come from a stackage snapshot) sometimes get shared between projects.
Note that you can list a relative path in the packages list, and point to this package. It will get built again, but it can be directly used in another project this way. Why the extra building? Stack has a different model of projects than cabal-install - it does not allow mutations to the package DB to affect how your other projects build.
One option for sharing such a package is to have it in a git repo and use https://docs.haskellstack.org/en/stable/custom_snapshot/ , but that stuff is still a bit new.
I have a project set up via stack and am importing a package dependency. I see that the package downloaded/installed successfully, so I had hoped that the REPL spawned by stack ghci would let me explore this package. To my surprise, there doesn't seem to be any sort of command for browsing a package. You can use :browse to look through a module, but I don't seem to have any way to see which modules are exposed by this package.
Is there any way to inspect a package in ghci? And if not, are there other ways to inspect a package? I know there are websites which provide documentation, but I want to ensure the information I'm seeing matches the actual version of the package which is installed.