How do you set up Haskell + ghc-mod on OS/X? - haskell

Question

I first set up Haskell from https://www.haskell.org/platform/ but ghc-mod had problems with sandboxes and to update it I needed a newer cabal which needed a newer ghc. Or something like that. (https://stackoverflow.com/a/28049104/131227 ??)
So I deleted everything, and installed from http://ghcformacosx.github.io/.
Then some strange failure setting up a new sandbox was because something didn't properly have a dependancy for happy. (https://github.com/haskell-suite/haskell-src-exts/issues/14)
Ok. Installed happy. Now trying (again) to install ghc-mod and I get a giant mess (below).
Should I use http://www.stackage.org/?
I've seen some people mention ghc-pkg recache or cabal install cabal-install... Are those things I need to do?
Mess:
Resolving dependencies... Configuring ghc-mod-5.2.1.2... Building ghc-mod-5.2.1.2... Failed to install ghc-mod-5.2.1.2 Build log ( /Users/mark/.cabal/logs/ghc-mod-5.2.1.2.log ): Configuring ghc-mod-5.2.1.2... Building ghc-mod-5.2.1.2... Preprocessing library ghc-mod-5.2.1.2...
Language/Haskell/GhcMod/Convert.hs:1:51: Warning:
-XOverlappingInstances is deprecated: instead use per-instance pragmas OVERLAPPING/OVERLAPPABLE/OVERLAPS [ 1 of 38] Compiling Language.Haskell.GhcMod.Read ( Language/Haskell/GhcMod/Read.hs, dist/build/Language/Haskell/GhcMod/Read.o ) [ 2 of 38] Compiling Language.Haskell.GhcMod.Cabal21 ( Language/Haskell/GhcMod/Cabal21.hs, dist/build/Language/Haskell/GhcMod/Cabal21.o ) [ 3 of 38] Compiling Language.Haskell.GhcMod.Cabal18 ( Language/Haskell/GhcMod/Cabal18.hs, dist/build/Language/Haskell/GhcMod/Cabal18.o ) [ 4 of 38] Compiling Language.Haskell.GhcMod.Cabal16 ( Language/Haskell/GhcMod/Cabal16.hs, dist/build/Language/Haskell/GhcMod/Cabal16.o ) [ 5 of 38] Compiling Language.Haskell.GhcMod.GHCChoice ( Language/Haskell/GhcMod/GHCChoice.hs, dist/build/Language/Haskell/GhcMod/GHCChoice.o ) [ 6 of 38] Compiling Language.Haskell.GhcMod.Error ( Language/Haskell/GhcMod/Error.hs, dist/build/Language/Haskell/GhcMod/Error.o )
Language/Haskell/GhcMod/Error.hs:12:1: Warning:
Module ‘Control.Monad.Error’ is deprecated:
Use Control.Monad.Except instead
Language/Haskell/GhcMod/Error.hs:40:10: Warning:
In the use of type constructor or class ‘Error’
(imported from Control.Monad.Error, but defined in Control.Monad.Trans.Error):
Deprecated: "Use Control.Monad.Trans.Except instead"
Language/Haskell/GhcMod/Error.hs:40:10: Warning:
In the use of type constructor or class ‘Error’
(imported from Control.Monad.Error, but defined in Control.Monad.Trans.Error):
Deprecated: "Use Control.Monad.Trans.Except instead" [ 7 of 38] Compiling Language.Haskell.GhcMod.Utils ( Language/Haskell/GhcMod/Utils.hs, dist/build/Language/Haskell/GhcMod/Utils.o )
Language/Haskell/GhcMod/Utils.hs:15:1: Warning:
The import of ‘Control.Applicative’ is redundant
except perhaps to import instances from ‘Control.Applicative’
To import instances alone, use: import Control.Applicative()
Language/Haskell/GhcMod/Utils.hs:45:51: Warning:
In the use of ‘strMsg’
(imported from Language.Haskell.GhcMod.Error, but defined in Control.Monad.Trans.Error):
Deprecated: "Use Control.Monad.Trans.Except instead" [ 8 of 38] Compiling Language.Haskell.GhcMod.Types ( Language/Haskell/GhcMod/Types.hs, dist/build/Language/Haskell/GhcMod/Types.o ) [ 9 of 38] Compiling Language.Haskell.GhcMod.Gap ( Language/Haskell/GhcMod/Gap.hs, dist/build/Language/Haskell/GhcMod/Gap.o )
Language/Haskell/GhcMod/Gap.hs:256:18:
Not in scope: data constructor ‘ExposePackageId’
Perhaps you meant ‘ExposePackage’ (imported from DynFlags) cabal: Error: some packages failed to install: ghc-mod-5.2.1.2 failed during the building phase. The exception was: ExitFailure 1
After applying the accepted answer (which seemed to install ghc-mod), running gch-mod gives the following:
> ghc-mod check x.hs
cabal-helper-wrapper: Installing a private copy of Cabal, this might take a
while but will only happen once per Cabal version.
If anything goes horribly wrong just delete this directory and try again:
/Users/mark/.ghc-mod/cabal-helper
If you want to avoid this automatic installation altogether install version
1.22.0.0 of Cabal manually (into your user or global package-db):
$ cabal install Cabal-1.22.0.0
...In order, the following would be installed:
filepath-1.3.0.1 (latest: 1.4.0.0) (new version)
directory-1.2.2.1 (new version)
process-1.2.3.0 (reinstall) changes: directory-1.2.2.0 -> 1.2.2.1,
filepath-1.4.0.0 -> 1.3.0.1
Cabal-1.22.0.0 (latest: 1.22.2.0) (new version)
cabal: The following packages are likely to be broken by the reinstalls:
ghc-7.10.1
Cabal-1.22.2.0
Use --force-reinstalls if you want to install anyway.
cabal-helper-wrapper: Installing Cabal version 1.22.0.0 failed.
nYou have two choices now:
- Either you install this version of Cabal in your globa/luser package-db
somehow
n- Or you can see if you can update your cabal-install to use a different
version of the Cabal library that we can build with:
$ cabal install cabal-install --constraint 'Cabal > 1.22.0.0'
nTo check the version cabal-install is currently using try:
$ cabal --version
ghc-mod: readCreateProcess: /Users/mark/.cabal/libexec/cabal-helper-wrapper "/Users/mark/work/haskell/ixberg/dist" "entrypoints" "source-dirs" "ghc-options" "ghc-src-options" "ghc-pkg-options" "--with-ghc=ghc" "--with-ghc-pkg=ghc-pkg" "--with-cabal=cabal" (exit 1): failed
Strangely, it wants the version of Cabal that is currently installed:
> cabal --version
cabal-install version 1.22.0.0
using version 1.22.0.0 of the Cabal library

Answer 1

Edit (August 2015) Better fix
A better command line tool for installing Haskell binaries and libraries by the awesome FPComplete group called stack means you can install ghc-mod with stack install ghc-mod (outside a project to make it global) and it will just work. The binary will be installed to ~/.local/bin and should be put on your path so your editor can find it.
I will leave the below for anyone who wishes to know what cabal Hell really meant.
Problem With DanielG's Fork
I asked on the Haskell reddit and NihillstDandy explained that the GHC for Mac OS X does not register the Cabal library. This is not true for your install from http://ghcformacosx.github.io/. It does register the Cabal library.
ghc-mod needs the cabal library to work, but it does not compile with the cabal library. Instead it compiles with cabal-helper and that looks to see if you have a registered version of the cabal library. If it does not find any then cabal-helper-wrapper will install a private copy and in this case it tired to install the same version as what cabal-install was compiled with, cabal-1.22.0.0.
When I installed DanielG's Fork it worked for my current project, but after testing it in other projects I am getting the same error you are. This is a problem with the fork and not Haskell (as far as I can tell).
Original Answer
So, while I was putting this post together ghc-mod was fixed for GHC-7.10. Thanks to DanielG!
git clone https://github.com/DanielG/ghc-mod
cd ghc-mod
cabal install -j4
And if you get errors that say "setup-Simple-Cabal-1.22.2.0-x86_64-osx-ghc-7.10.1: The program 'happy' version
>=1.17 is required but it could not be found."
cabal install happy -j4
The same for any other problems and it should work. (Although you have happy installed, so it should just work).
The rest of the post is on how to downgrade the cabal executable, also known as cabal-install, to version 1.20.0.3. Although you could really use this to downgrade to any version. Since there is a working fork of ghc-mod that works with GHC-7.10 and cabal-1.22 you do not need to downgrade to fix ghc-mod.
I'm just leaving the rest of the post up here since, unfortunately, this is a problem with Haskell as a whole. Halcyon and nix are ways to deal with Haskell's shortcomings in this regard.
How to downgrade Cabal in Haskell
When I wrote this post ghc-mod, nor any fork, compiled with GHC-7.10 and versions below 7.10 broke with cabal-1.22 sandboxes.
However, even if you compile ghc-mod with GHC-7.8.4 (the version before 7.10) and cabal-1.20.0.3 you still cannot use ghc-mod inside a sandbox created by cabal-1.22 and above. So the only way to use ghc-mod is to either downgrade your entire system to cabal-1.20.0.3 or don't use sandboxes. This means you can still use GHC-7.10, but you have to use the older version of cabal. That is unless you want to wait until the convener or someone else fixes it for GHC-7.10. Its been over a week already, but some kind Haskell programmer fixed it in a fork (see above).
If this is something you still want here is how to compile ghc-mod with GHC-7.8.4 and cabal-1.20.0.3. Also, I replace the executable cabal-1.22 with the older cabal-1.20.0.3. Note, it does not matter what directory you download the sources to.
download GHC-7.8.4 source for your OS from here
tar -xf path_to_zipped_source
cd path_to_ghc-7.8.4
The next steps will install ghc-7.8.4 as ghc-7.8.4 in the same folder as ghc-7.10 is install for you. The -j4 is to tell make to use 4 threads to compile it.
./configure
make install -j4
To get the correct version of cabal we can just ask cabal to get it.
cabal get cabal-install-1.20.0.3
cd cabal-install-1.20.0.3
Now to install cabal with ghc-7.8.4. Here cabal-1.22 will pull all the decencies and should give you some warning about installing another version of the cabal library (not to be confused with cabal-install), this should not cause problems.
cabal --with-compiler=ghc-7.8.4 install
So now you should have cabal-1.20.0.4 installed, but not on your path. It will be in ~/.cabal/bin. We need to make this global, so remove cabal-1.22 (it only removes the symlink).
rm `which cabal`
And create the symlink to cabal-1.20.0.4. Btw, you will need to remove any sandboxes you made with cabal-1.22 and remake them with cabal-1.20.0.4.
If you do not have realpath you can just type in the full path of cabal. I use it for connivence.
cd ~/.cabal/bin
ln -s `realpath cabal` /usr/local/bin
Now this is how I compiled ghc-mod on my mac (you may run into your own problems). I'm not sure why cabal couldn't do it in one call, but this worked in the end.
cabal --with-compiler=ghc-7.8.4 install happy
cabal --with-compiler=ghc-7.8.4 install haskell-src-exts-1.16.0.1
cabal --with-compiler=ghc-7.8.4 install hlint-1.9.19
cabal --with-compiler=ghc-7.8.4 install ghc-mod
Now you should be able to call ghc-mod from anywhere. To test it just type ghc-mod after you have cabal sandbox init. If it does not throw any errors then your in the clear.

Answer 2

The version of executable cabal that is used to configure this project should be the same as the version of the global Cabal package.
It's easier to install a compatible version of cabal-install than Cabal as follows:
$ ghc-pkg list | grep Cabal
Cabal-1.22.2.0
$ cabal install cabal-install-1.22.2.0
Or build one in sandbox and replace/shadow the original one.
Then don't forget to re-configure the project with the new cabal:
$ cabal clean && cabal configure
Now the ghc-mod should works.

Answer 3

If Cabal-1.22 isn't registered (ghc-pkg list cabal), the cabal-helper-wrapper will install a private copy because it needs the library installed to work, but it doesn't want to stomp on anything you have that might break by upgrading Cabal directly.
GHC for Mac OS X doesn't register the Cabal library, it comes bundled with a version of cabal-install built against it.