Haskell Support in Mainstream IDEs
I've tested out the Haskell support of the top mainstream IDEs. Here's
a rundown of the current state of things.
As a dyed-in-the-wool Emacs hacker I've never used any of the more
recent mainstream IDEs, so I can probably offer an unbiased review of
the support provided by each.
Note: I tried approaching it as a client would, or prospective Haskell
user, so for any manual intervention I had to do, I've used a tone
that indicates I'm not happy about having to do it, and anything that
doesn't just work I just discard with little patience, as a real
person would and do today. Even if I know there are probably extra
manual investigations that I could do knowing what I do about Haskell,
a normal user wouldn't have that advantage.
I installed it according to the
instructions on the IntelliJ IDEA web site. I
downloaded it to my Ubuntu laptop and installed it under
After installing IntelliJ, running it opens up a splash screen. Rather
than starting a project, I went straight to the Configure->Plugins
button. In the plugins list, I chose
IntelliJ-Haskell. After that,
it was suggested that I restart, so I hit
After restarting, on the splash screen I hit Create New Project and
chose "Haskell module". At this point, it asked me to "Select the
stack binary". I picked the one at
someone else might find it under
/usr/local/bin/stack. I hit Next.
Warning: there was a long wait after this step. I entered my project
name and proceeded. Opening the project workspace, it now claims "busy
installing hlint", which is a Haskell linting tool. It does this for
various tools; hlint, hindent, stylish-haskell, hoogle. This took
easily 15 minutes on my machine. Go make a cup of tea.
Finally, after finishing this process, it's ready to go. Here are some
things that I observed work correctly:
- Compile errors when changing code on the fly. Slow, but works. You
can hit the "Haskell Problems" tab to see the actual compiler
- Hitting Ctrl and mousing over something, which is how you get
metadata in IDEA.
- Go to definition of library code.
- Go to definition of local code.
- Type info at point.
- Go to definition of local bindings.
I tested this out by opening the Stack codebase itself. Took about 10
seconds on "Indexing..." and then was ready.
There's a very picky set of steps to opening an existing project
- You have to go "Create project from existing source"
- Choose "Create from external model"
- Choose the "Haskell" SDK.
Then it should be good to go. Other ways didn't work for me and I got
I've also seen that it's possible to define test and executable
targets quite reasonably.
IntelliJ has support to "optimize imports" which will remove unneeded
ones, which is very common when refactoring. I'd call that feature a
Overall, this IDE experience is not bad. As a Haskeller, I could get
by if I had to use this.
Visual Studio Code
I followed along with the
install instructions for Linux. I
downloaded the .deb and ran
sudo apt install ./<file>.deb.
I launched Visual Studio Code from the Ubuntu Activities menu. It
displays its full UI immediately, which was quite a lot faster than
IntelliJ, which takes about 5 seconds before displaying a UI
window. Not that I care about start-up times:
I use Emacs.
Visual Studio Code: Haskero
I went to the Customize section and then "Tools and languages". Up
pops a menu for language choices (also quite quickly). I tried
plugin, which, as I understand, is in spirit the same backend and
functionality of IntelliJ-Haskell. It said "This extension is enabled
Assuming that it was ready to use, I looked for a way to create a
project. I didn't find one, so I opted to try opening an existing
Haskell project: stack. I used File -> Open Workspace and chose the
repository root directory.
VSC reports "Unable to watch for file changes in this large
workspace." I followed
the link which had a hint to increase the limit. I
sysctl.conf file as instructed to allow VSC to watch all
the files in my project.
Opening, for example,
src/main/Main.hs, it opens quickly, but
doesn't appear to be doing any work like IntelliJ was. So I create
some obvious errors in the file to see whether anything works.
After waiting a while, it seems that I have to save the file to see
any kind of reaction from VSC. So I save the file and wait. I timed
Wed 13 Nov 10:09:38 CET 2019
Wed 13 Nov 10:10:40 CET 2019
After a full minute, I got in the Problems tab the problem.
It seems to be recompiling the whole project on every change. This
pretty much makes this plugin unusable. I don't think the author has
tested this on a large project.
In its current state, I would not recommend Haskero. I uninstalled it
and decided to look at others.
Visual Studio Code: Haskelly
I decided to try the other similar offering called
Haskelly. After a reload and re-opening Stack, I made an intentional
src/main/Main.hs again and found that nothing happened. No
CPU usage by any process.
There weren't any indicators on the screen of anything failing to
work. However, I had an intentional type error in my file that was not
flagged up anywhere.
Another plugin that I would rate as not usable. I uninstalled it.
Visual Studio Code: Haskell Language Server
I installed the "Haskell Language Server", which is supposed to be the
latest state of the art in language backends for Haskell.
Enabling it, I see the message:
hie executable missing, please make sure it is installed, see
Apparently I have to manually install something. Okay, sure, why not?
a variety of installation methods. I'm
not sure which one will work. But I already have
stack installed, so
I try the install from source option:
$ git clone https://github.com/haskell/haskell-ide-engine --recurse-submodules --depth 1
This seems to clone the whole world and takes a while. Definitely a
get a cup of tea moment. After that was done, I went to the directory
and ran this as per the instructions:
$ stack ./install.hs help
I am presented with a myriad of options:
stack-build Builds hie with all installed GHCs; with stack
stack-build-all Builds hie for all installed GHC versions and the data files; with stack
stack-build-data Get the required data-files for `hie` (Hoogle DB); with stack
stack-install-cabal Install the cabal executable. It will install the required minimum version for hie (currently 184.108.40.206) if it isn't already present in $PATH; with stack
stack-hie-8.4.2 Builds hie for GHC version 8.4.2; with stack
stack-hie-8.4.3 Builds hie for GHC version 8.4.3; with stack
stack-hie-8.4.4 Builds hie for GHC version 8.4.4; with stack
stack-hie-8.6.1 Builds hie for GHC version 8.6.1; with stack
stack-hie-8.6.2 Builds hie for GHC version 8.6.2; with stack
stack-hie-8.6.3 Builds hie for GHC version 8.6.3; with stack
stack-hie-8.6.4 Builds hie for GHC version 8.6.4; with stack
stack-hie-8.6.5 Builds hie for GHC version 8.6.5; with stack
I lookup the GHC version that's being used by the stack source code:
~/Work/fpco/stack$ stack ghc -- --version
The Glorious Glasgow Haskell Compilation System, version 8.2.2
Apparently the GHC version in use by stack is too old. At this point I
stop and uninstall the plugin.
Visual Studio Code: ghcid
As a last resort, I tried one more plugin. But nothing seemed to
happen with this one either. So I uninstalled it.
Another popular editor is SublimeText. I installed it via the apt
documented here. I
decided to try the
plugin which seems popular.
Installing things in SublimeHaskell is a little arcane: you first have
to install "Package Control". I don't remember which menu item this
was from. However, SublimeText installs this for you. Once that's
done, you have to use Tools->Command Pallete, which is a kind of
quick-access tool that's apparently common in SublimeText. In there
you have to literally type "package control" and then go to "Package
Control: Install Package" and hit RET. Then you can type
SublimeHaskell and hit RET. As an Emacs user, I'm not afraid of arcane
After installing, it pops up a dialog with:
No usable backends (hsdev, ghc-mod) found in PATH. [..] Please check
or update your SublimeHaskell user settings or install hsdev or
It displays a tab with the README from SublimeHaskell and I assume
this is where SublimeText is done helping me.
Okay, let's install hsdev!
I had to create a file
And then run
$ stack install hsdev --stack-yaml hsdev.yaml
That took 5 minutes but succeeded. There isn't a "next button" on
SublimeText, so I just restarted it. I did File->Open Folder and
opened the stack directory and the
I see "Inspecting stack" which indicates that it's actually doing
something. However, after that finishes, I still don't see any error
messages for my type error. Finally, I make a new change and save the
file, and a little messages area pops up below.
Could not find module ‘Data.Aeson’
And so one for pretty much every library module in the project.
At this point I can't find a menu or anything else to help me
configure packages or anything related.
At this point it seems like SublimeText is almost workable. The cons
appear to be the manual install process, and the complete lack of
guidance in the user experience. I'm afraid I can't recommend this to
clients either at the moment.
The story for Visual Studio Code is pretty dire. I did not find a
straight-forward install or reliably working IDE for Haskell in Visual
Studio Code, and therefore, at the moment, cannot recommend it to our
clients. Perhaps a little work done on Haskero could bring it up to par.
SublimeText falls over at the finish line. It seems like with a little
work on the user experience could bring this up to par.
IntelliJ IDEA however worked quite well with little to no intervention
required. So I would indeed recommend it to clients.
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