The source tree for happy contains AttrGrammarParser.ly and Parser.ly and the source tree for alex contains Scan.x. Yet, as far as I can tell in order to compile happy, we need to transform the .ly files into .lhs files using... happy, and in order to compile alex we need to transform the .x files into .hs files using... alex.
So it seems like there must be some bootstrapping going on here in order to compile either tool.
The Setup.lhs files for each project contain some template expansion, but, as far as I can tell, don't do anything in particular to do the bootstrapping.
How and where is the bootstrapping done?
I see that you are looking at the source tree of the darcs repositories for these packages on darcs.haskell.org. If you look at the actual tarballs on Hackage, you'll see something a bit different:
https://hackage.haskell.org/package/alex-3.1.4/src/dist/build/alex/alex-tmp/
https://hackage.haskell.org/package/happy-1.19.5/src/dist/build/happy/happy-tmp/
So basically the build artifacts necessary are shipped with the Hackage tarball. Cabal then just uses the build artifacts during the build process, thus avoiding the need to bootstrap locally. Cabal also knows how to preserve such build artifacts when you run cabal sdist for your own packages which you want not to depend on happy or alex, but last I checked this doesn't interoperate well with sandboxes, fwiw.
By the way, alex and happy development has moved to github:
https://github.com/simonmar/alex/
https://github.com/simonmar/happy/
Related
I try to use
Control.Monad.Extra.andM
import Control.Monad.Extra (andM)
but has an error:
Could not find module ‘Control.Monad.Extra’
Perhaps you meant
Control.Monad.Catch (needs flag -package-key exceptions-0.10.4)
Control.Monad.Error (needs flag -package-key mtl-2.2.2)
Control.Monad.Except (needs flag -package-key mtl-2.2.2)not found
This error does not make sense.
According to
https://cabal.readthedocs.io/en/3.6/installing-packages.html#installing-packages-from-hackage
3.2.1. Installing packages from Hackage
The cabal tool also can download, configure, build and install a Hackage package and all of its dependencies in a single step. To do this, run:
$ cabal install [PACKAGE...]
To browse the list of available packages, visit the Hackage web site.
Which says "in a single step", but in my experience this is too complicated and actually I have no idea how to install Control.Monad.Extra .
Usually, when a Haskeller want to install a specific library/package like this, how do you do this? There's no adequate documentations, it seems.
How to install an library in Haskell?
You don't. You should just depend on them, and then let Cabal worry about any installations that may need to be done. I.e., as you wrote
Go to the Hackage page and study which exact library to be used.
*.cabal file -> build-depends: extra >=1.7.10
This is the crucial step. Your own Cabal file is the way to both specify what libraries are needed right now, as well as ensuring that everything will still work in the future. This file needs to specify both the packages you require, as well as the modules you're defining yourself.
Probably you don't actually need >=1.7.10, but it can't hurt much to be specific there. Standard practice is to add both lower and upper bounds on the x.y level, i.e. you'd use extra >=1.7 && <1.8, and then push the upper boundary as new versions come out. Arguably this is a bit overcautious; if you only use some simple tools from a package that is unlikely to have breaking changes in the future then it may be less trouble to just leave the upper boundary out.
$ cabal install extra
You've already specified that extra is needed for your project, no need to state that again. Instead, simply build your own project now.$ cabal buildor, to get a GHCi prompt with your modules,$ cabal replor, if you have an executable with a main that you wish to execute$ cabal runor if you want to install that executable (and only then)$ cabal installCabal will then automatically figure out that extra-1.7.10 should be installed first.
(In old Cabal it would still have been necessary to run cabal install --dependencies-only first.)
Ok Self-Answered. Comment me if the information is wrong.
1. Go to the Hackage page and study which exact library to be used.
In this case, it seems extra-1.7.10.
2. *.cabal file -> build-depends: extra >=1.7.10 (among other libs)
3. $ cabal install extra
Error:
cabal: Cannot build the executables in the package extra because it does not contain any executables. Check the .cabal file for the package and make sure that it properly declares the components that you expect.
Well, I did for sure.
4. cabal install extra --lib
Finally works, but the documentation never said this.
Am I correct?
`
Is this the only method? or any other smarter way?
Do I need to manually edit the *.cabal file's build-depends section to add package as a project dependency?
Or perhaps there is a more convenient way that is not as error prone as manually mangling with build files is.
Thinking about functionality that pretty much any package manager I used has, namely
apt install
npm i
nuget install
Install Package
and so on. Does such functionality exist in Cabal?
There is no better way at the moment. The answer #danidiaz gave is essentially correct -- cabal-edit will automatically update cabal files for you. The plan is to import similar functionality into cabal directly. This was remains blocked on an exactprinter that can parse and emit cabal files precisely -- and work on that exactprinter is now underway.
Is it possible to install package from sources with something similar to stack build package-name? (latter works with packages on Stackage, but not with custom ones)
Um, stack build (within the source directory)?
Stack doesn't really have a notion of installing libraries though, it only installs executables. To “install” locally-sourced packages, you need to specify what for you want them installed: add them as dependencies to another project, via a location: field in the packages: field in that project's stack.yaml file.
That's arguably sensible since, one might say, there's nothing you can do with an installed library except invoking it in another Haskell project (or in a REPL, which you can get with stack ghci). I personally don't hold with that though, I like actually being able to say install that library now. Which is one of the reasons I have always stuck to good old cabal-install rather than Stack. With that, you can just
cabal install
from within the source directory.
Cabal-install has often been criticised: its local installs can easily get out of sync and then you have weird dependency conflicts and need to rebuild lots of stuff. I never found this that much of a problem, and anyway this has been adressed in recent Cabal through Nix-style builds, which never produce conflicts.
I'm attempting to start a new project using the Snap web framework. I used snap init to get my basic skeleton working. I also put http://www.stackage.org/lts/cabal.config next to my .cabal file. I didn't uncomment the line to use Stackage exclusively. So I tried to build and it failed and couldn't find the version of lens required by my .cabal file. The cabal.config file from Stackage specifies a version of lens that is not the same as the one in my .cabal file. So I deleted every constraint from my package list and did the usual cabal install --only-dep -j8 --enable-test and it worked!
However, I have always been told that package versions should be constrained. So when working with Stackage is it okay to leave package versions unconstrained? Should I downgrade my packages to the ones available in Stackage instead?
As far as I understand a cabal.config file specifies a set of dependencies with the specific versions that satisfy dependencies, so how does Stackage work? Is it just a subset of packages from Hackage that are proven to be compatible? Do they host their own packages or rely on Hackage for downloads?
Thanks in advance :)
Both options are available. The default option is what you did, and still goes to hackage to get the packages. You just added a filter to your cabal that prevents you from using any version of a package included in Stackage that was not tested to work together with all of the other packages.
The other option is to simply point your cabal repo to a Stackage url, and then you will download packages directly from the Stackage server. That server will only serve packages that are known to work together, so there is no need for additional constraints in your cabal file. I actually prefer this way of working.
In both cases, if you have additional constraints in your cabal file that are incompatible with the Stackage restrictions, your build will fail. If you use the first option, you will get dependency conflicts. When using the second option, the Stackage server will simply report that it does not have that specific package/version.
After I upload my package into hackages, it didn't generate haddock as others packages.
Anything I missed?
What I did is:
cabal dist and a package generated under dist directory.
open hackage web upload interface and upload the package.
open the URL and turns out package uploaded successfully but no haddock.
(the package do have a few docs)
Thank you.
Docs take a little bit of time to generate. I believe they are ran at midnight GMT.
In addition to Thomas's answer, run cabal haddock in your package directory and look for any errors.
Haddock is incredibly finicky in my experience, especially wrt. code blocks. If you get a parse error, just start deleting comments until docs can be generated. I usually use some extensively-documented package as a reference.
It looks like the documentation is missing because your package didn't build correctly. I found this near the end of the build log:
src/Network/OAuth2/HTTP/HttpClient.hs:18:8:
Could not find module `Control.Monad.Trans.Resource'
It is a member of the hidden package `resourcet-0.3.2.1'.
Perhaps you need to add `resourcet' to the build-depends in your .cabal file.
Use -v to see a list of the files searched for.
To avoid these sorts of problems, make sure your package builds locally with Cabal before uploading. Building with GHC directly will often mask these sorts of problems, since it will happily use whatever packages you have installed, regardless of whether you've mentioned them in your .cabal file or not.