I want to use HList: Heterogeneous lists, but the package seems not on Stackage.
I currently use stack. In this case what is the option besides going back to use Cabal?
Use extra-deps in stack.yaml:
extra-deps:
- HList-0.5.2.0
Stack should prompt you to if you add the package as a dependency in the Cabal file.
Related
I have a Haskell library I wrote that I compile with stack.
I now need to use it in another Haskell stack project.
In order to do that, I have added its current version to the extra_deps of my new project's stack.yaml and listed it among the build_depends of one its executables.
When I run stack build, however, it obviously tries to download the library from the internet. How do I specify that the library is local and where to find it?
Thanks in advance!
You can use github coordinates in the extra-deps section of your stack.yaml.
extra-deps:
- github: snoyberg/http-client
commit: a5f4f30f01366738f913968163d856366d7e0342
Then add the dependency in your package.yaml:
dependencies:
- http-client >= 0.1.0.0
I am working on my first major Haskell application, and want to add mockery to create disposable test WAI threads. Importing mockery and running stack test resulted in the compiler error:
Failed to load interface for ‘Test.Mockery.Directory’
It is a member of the hidden package ‘mockery-0.3.5’.
Perhaps you need to add ‘mockery’ to the build-depends in your .cabal file.
Use -v to see a list of the files searched for.
So, I added mockery to my cabal file under test dependencies. However, when I run stack build or stack test mockery is automatically removed from the cabal file.
I have also tried listing mockery-0.3.5 under extra-deps in the stack.yaml file. This unsurprisingly didn't work, since mockery is part of my lts, and extra deps is for packages outside of lts.
How can I get stack to recognize that mockery should be included as a dependency to to project?
Here is my stack.yaml:
flags: {}
ghc-options:
! '*': -Wall
packages:
- .
extra-deps: [
]
resolver: lts-9.5
I'm using stack version 1.5.1
I imagine this is a stupid build issue and look forward to confronting my obvious oversight.
In stack.yaml you declare the Stackage LTS version, a curated list of hackage dependencies that you want to depend on. You can also depend on local packages and packages in git that are not in Hackage. You may also change the versions of the packages in LTS as long as they respect the constraints of the other dependencies.
package.yaml is the build file. Any packages you want to import directly in your Haskell code must be declared in here as dependencies, even if they are explicitly declared in the stack.yaml.
Finally, when you see It is a member of the hidden package, that means that one of your dependencies is using that package, but it is not declared as a dependency in your build file.
I want to use reactive-banana in my new Haskell project. I never used cabal-install or stack before. I created a directory and initialized project files in it using stack new. I see now 2 files in the directory: new-template.cabal and stack.yaml.
How do I set dependencies and make sure they are downloaded and compiled?
At first I tried to add - reactive-banana-0.8.0.2 in stack.yaml under extra-deps:, but both stack build and stack solver didn't download it. Then I augmented a part called library in new-template.cabal to this:
library
hs-source-dirs: src
exposed-modules: Lib
build-depends: base >= 4.7 && < 5
, reactive-banana >= 0.8
default-language: Haskell2010
Every time I tried to run stack build, it crashed with an error and suggestion to add some package to stack.yaml under extra-deps:, and this happened three times until finally all packages installed, and I could import them in stack ghci REPL.
So my question is, what is the idiomatic way to use stack? Which of these 2 files should I use to specify dependencies and other project metadata? What is the sample workflow of an average Haskell developer with stack?
When using stack I generally don't put any versions bounds in my .cabal file. I let the resolver and extra-deps setting in the stack.yaml file determine which versions of packages to select.
Here is a stack.yaml file which brings in reactive-banana-0.8.1.2:
flags: {}
packages:
- '.'
extra-deps:
- reactive-banana-0.8.1.2
- psqueues-0.2.0.2
resolver: lts-2.17
In my .cabal file I just have:
build-depends: base >= 4.7 && < 5, reactive-banana
The reactive-banana version is pinned by the stack.yaml file.
If you want to use GHC 7.10 change the resolver to something like nightly-2015-06-17.
I determine the extra-deps iteratively, by just running stack build and adding whatever dependencies are missing to the stack.yaml file until all dependencies are satisfied.
You will only need to do this with packages which are not in Stackage - like reactive-banana. A great many of commonly used packages are in Stackage and their versions will be determined by the resolver setting.
In the default configuration, stack works with two package databases: a centralised per-user one and a project-specific one. The centralised database only pulls packages from Stackage, a subset of Hackage with known-to-be-compatible packages, while you can put whatever you want on the project-specific database. All packages you use must be in the cabal file, but those not on Stackage (that is, the ones that will go to the project-specific database) must also be listed in the extra-deps section of stack.yaml. reactive-banana is not on Stackage, so you need to add it to stack.yaml, like this:
# etc.
extra-deps:
- reactive-banana-0.8.1.2
# etc.
stack solver can fill in the extra dependencies in stack.yaml for you.
Using cabal, I could install hakyll with the command:
cabal install hakyll
How can I do the same thing using stack?
stack install hakyll
stack offers a curated set of packages that won't blow your machine up. If you want to check what packages are available, or exactly what version is supported, or on what version of GHC you can get it, check out https://www.stackage.org/.
For example, you can get hakyll 4.6.9.0 right now for both GHC 7.8.4 and GHC 7.10.1. Pretty neat. - source
EDIT: I forgot to mention, Yuan Wang's method works for getting the version of hakyll that is not curated into stackage. It's up to you what version you need.
add hakyll in stack.yaml generated by stack init or stack new
yaml file should look like:
flags: {}
packages:
- '.'
extra-deps:
- hakyll-4.7.1.0
resolver: lts-2.15
after that, run stack solver installs it
https://github.com/commercialhaskell/stack/wiki/stack.yaml
This documentation worked for me
On package.yaml add the library under dependencies, for example:
dependencies:
- base >= 4.7 && < 5
- hakyll # added here
I recently ran into a Cabal issue that I only managed to solve by manually installing transformers-compat with the -f transformers3 flag in my cabal sandbox before running cabal install for my project.
Is there any way to indicate in my application's .cabal file that I depend on a library so that it is built with the specific build flag?
Newer versions of Cabal let you specify constraints in your cabal.project.local or cabal.project file. For example:
constraints: hmatrix +openblas
Is there any way to indicate in my application's .cabal file that I depend on a library so that it is built with the specific build flag?
No, but in your case this is not actually a problem in the solver and is rather and uninformative error (caused by someone's less than judicious uses of flags).
Looks like it's not possible to specify such a dependency via the build-depends field in your .cabal file. buildDepends is defined as [Dependency], where data Dependency = Dependency PackageName VersionRange. You can use cabal install --constraint="transformers-compat +transformers3", though.
Looking at the transformers-compat.cabal file, I think that the solver should be able to figure out the correct flag assignment if you constrain your dependency on transformers appropriately. E.g. build-depends: transformers >= 0.3 && < 0.4 should force the solver to choose transformers-compat +transformers3. If this doesn't work, it may be a bug in the solver.
I also struggled for a long time to find a solution to this problem. I just found one! You have to modify the global cabal configuration file at ~/.cabal/config. Add a constraints line like this to the initial section of the file:
constraints: hmatrix +openblas
This enables the openblas flag for the hmatrix package. It will be used automatically the next time the package is installed. If there is a way to set such a flag locally for a sandbox, I could not find it.
You cannot do this with Cabal.
One way to do this is to use Stack. Edit your stack.yaml to include
flags:
transformers-compat:
transformers3: true
See also the section on flags.
cabal now supports an elegant way to do this similar to stack, through cabal.project configuration options.
package transformers-compat
flags: +transformers3
will add the flag transformers3 when building the package transformers-compat.
There are a couple of ways to constrain the version for installation.
Add lower and upper bounds to package versions in the cabal file like Mikhail mentioned above, example of such a file here
Additionally, you can override the settings in the .cabal file with the flag cabal install --constraint="bar-2.1"
To remove a specific version of a package:
In a sandbox you can unregister a version with cabal sandbox hc-pkg unregister bar-2.1
Global unregistering can be done with this command outside of sandbox ghc-pkg unregister bar-2.1