When I use the data-files feature of cabal, it generates a Paths_pkgname.hs module that lives in the dist/ folder.
However, intero is unable to find this file (or generate it on its own), and I can't find any means to pass an option to hint at its position.
Note: Somewhere else (on SO?) I picked up the trick when using ghci to make a dummy only-for-ghci/Paths_.hs that is only brought into scope through :set -ionly-for-ghci being set in .ghci. This won't apply for intero though, as its invocation in intero.el specificcally instructs it to ignore the .ghci file.
I was only building my project using cabal and nix. It turns out that because Intero is stack-centric, building the project with stack build does indeed put a Paths_.. module in a place where Intero searches.
Related
How can I "install" a local (ie it is on my hard-drive, not on the internet) .hs file to use it across multiple programs? Specifically, if I edit the library, those edits should be available to all programs, so no copy-pasting the library into every program’s directory.
To compile my programs, I still want to type ghc main.hs, not a page of file-paths.
This may be obvious from the above, but I don’t have any knowledge of cabal.
Make sure you have the proper Haskell platform installed, including cabal. Alternatively you can use stack, which is more modern and in many ways better, but IMO cabal is still more practical for a simple project like yours.The following assumes you use cabal on a typical Linux machine.
If not already done, give your file a meaningful hierarchical module name, according to what it does. module Video.Demuxing.FFMPEG or Data.List.Shuffle.Deterministic, for example. Let's assume you call it Foo.Bar.Baz. I.e. the file should begin with
module Foo.Bar.Baz where
... -- start code
Put the file in a corresponding folder structure, i.e.
if not already done, make a new project directory, for example
mkdir /home/Uꜱᴇʀɴᴀᴍᴇ/haskell/foobar
cd /home/Uꜱᴇʀɴᴀᴍᴇ/haskell/foobar
In that project directory make a subdirectory Foo, therein a directory Bar, and put your file in it as Baz.hs.
mkdir -p Foo/Bar
cp WʜᴇʀᴇEᴠᴇʀ/Yᴏᴜʀ/Fɪʟᴇ/Wᴀꜱ/Bᴇꜰᴏʀᴇ.hs Foo/Bar/Baz.hs
Make the file part of a new cabal library.
cabal init
This will ask you a couple of questions, hopefully it'll be clear what to choose. For the most part, the defaults will be fine, in that case always just press enter.
Put everything under version control, if you haven't already. (If you don't know what this is, I suggest you read some Github tutorials. You can skip this step, but the sooner you accustom yourself to some VCS, the better.)
Install your project locally.
cabal install
If everything has worked without errors, you can then, in a Haskell file stored in somewhere else on the computer, simply
import Foo.Bar.Baz
and have everything availably you've defined in that project module. No need to tell GHC where Foo.Bar.Baz is stored when compiling, it has already registered that at this point. You can also launch up ghci anywhere and :m +Foo.Bar.Baz.
Syntastic works great in my system with hdevtools and hlint. But if I'm editing a file under a test directory, importing packages that are exclusively under the test-suite configuration of the cabal package, it marks my imports as bogus and tells me to include them in my cabal file. The same problem happens with the hs-source-dir, it only finds the ones under the library or executable directory.
There is no silver bullet. You can either set g:syntastic_haskell_hdevtools_args and friends to the proper flags for your project, or write a wrapper script similar to this and point g:syntastic_haskell_hdevtools_exec to it. Syntastic has no built-in support for looking at cabal files.
I am using Alex 3.0.5, Happy 1.18.10, Cabal 1.16.0.2
I have a small compiler project that is built using Cabal. I am exposing the compiler's internals as a library, so I have in the exposed modules section, MyLangLex and MyLangPar. If I delete the .hs files that are generated by Alex and Happy, then running cabal configure, and then cabal build will run Alex and Happy first, generate the files, and then proceed with the build, and everything works as expected. However, if I do not delete these files, Alex and Happy either do not build the files, or they don't put them in the right place. I think Happy runs, because I see a message from Happy; however, when I look at the .hs file that should be generated it is incorrect (doesn't have a change in it), and I can tell for sure that the version of the .hs file that Cabal uses in the build is the wrong one because the behaviour that should have changed does not. I.e. The change to the .y file does not get incorporated into the built program, so I suspect that while Happy is run, Cabal places this file in some temp directory, and then uses the old .hs file, which is still there for the build. But I am not sure about this.
Is the error on my part or is one of the tools misbehaving?
It sounds like you need a "other-modules:" directive in your library section for Lex.x and Par.y:
library
...
build-tools: alex, happy
other-modules: Compiler.RSL.Syntax.Lex, Compiler.RSL.Syntax.Par
The other-modules directive together with build-tools will instruct cabal to use alex and to create Compiler/RSL/Syntax/Lex.hs from the .x file if it doesn't exist (and the same for Par.hs).
Alternatively, add Compiler.RSL.Syntax.Lex to your 'exposed-modules' list. This tells cabal that the Lex.hs file should exist, and so if it doesn't cabal will look for ways to build it using the tools in the build-tools line.
I've added a putStrLn "Hello" line into main function of my Setup.lhs and was expecting to see it when running cabal configure or cabal build. But i did not.
Then i've compiled Setup.lhs with ghc --make and ran ./Setup configure and the line was shown.
If it's done intentionnaly, i don't see rationale behind this and even need in Setup.lhs file at all. Can you clear these things for me?
You most likely have
build-type: Simple
in your .cabal file. If you select the Simple build type, you essentially promise that your Setup file does nothing but invoke defaultMain, and the cabal binary will not invoke it. If you want to ensure that your Setup file is run every time, then change the line to
build-type: Custom
You also ask about the rationale for requiring the Setup file anyway: actually, it isn't required if you use the Simple build type. The cabal binary will happily configure and install it without. However, it is considered good style to include a Setup file for any package, because it will allow users to install the package who have the Cabal libary available, but not the cabal-install tool (and Hackage enforces the presence of a Setup file for this reason).
I'm trying out HAppStack. I installed HAppStack and created a project: happstack new project web. New folder 'web' created with project guestbook under it. So now I want to run it. The only way I could do it is run cabal install. But I want to run my app without installing with cabal! Executing run.sh errors: Could not find module 'Paths_guestbook'. How can I do it?
Edit:
In general, is there a way to run HAppStack app without rebuild like in Snap?
In general, you can always build Cabal projects without installing simply by doing:
$ cabal configure
$ cabal build
The resulting executable will usually be called dist/build/<project>/<project>.
The specific error you're getting is because the code must be built with Cabal to get the Paths_guestbook module, which will contain information about the location of data files used by it. (It may be the case that it's unable to find these data files if you run the executable without installing it; in that case, you'll need a more elaborate solution, such as cabal-dev.)
(I'm not a Happstack user, so I don't know if there's an official way to accomplish this, but this should work for basically any Cabal-based project in general. The repository shows that run.sh was last modified in 2009, so I suspect it has simply bit-rotten. It doesn't do anything special, though, so cabal build should work just fine.)
SHORT VERSION:
The run.sh seems to be missing an include paramater. Modify it to look like this:
#!/bin/sh
runghc -isrc -isrc-interactive-only src/Main.hs
I have update the run.sh in darcs to include this change.
LONG VERSION:
Normally that flag is not needed for Happstack applications. You can usually just do, runhaskell Main.hs. But in that particular example the Main.hs explicitly imports:
import Paths_guestbook (version)
which is used in the versionInfo function so that the server can report its own version number. Though version number in src-interactive-only is hardcoded and will generally be out of date. So it is only correct if you actually build with cabal.
The Paths_guestbook module is normally created automatically when cabal build is run. So, another fix would be to change the run.sh to:
#!/bin/sh
runghc -isrc -idist/build/autogen src/Main.hs
And run cabal configure && cabal build once. After that you will be able to use run.sh (until you do a cabal clean).
Another option would be to set a CPP flag in the .cabal file, and only import Paths_guestbook when the application is being built via cabal.
For example in the happstack.com source code:
http://patch-tag.com/r/stepcut/happstackDotCom/snapshot/current/content/pretty/Main.hs
In line 40 (or so) you will see an #ifdef __CABAL__. happstack.com needs to be able to know where to find the static content such as .css files. When doing runhaskell Main.hs in the local directory, it will look for the files in a sub-directory of the local directory. If you do cabal install it will instead look whever cabal installs the data files. Or, you can override the default location with command-line arguments. (Which is what the debian packaging for that app does).
Unfortunately, the happstack new project command is somewhat bitrotten because the author became a parent and has not had time to work on it in a long time. It will likely be removed from the upcoming Happstack release in order to reduce confusion.
In order to be truly useful, I think the command needs to prompt for a bunch of values and then generate a new project from a set of templates. Similar to how 'cabal init' works. But currently, no one has volunteered the time to make that happen.
To see changes to your source appear automatically with out restarting the server you can use the happstack-plugins library. There is an screencast of it here:
http://happstack.blogspot.com/2010/10/recompile-your-haskell-based-templates.html