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.

IntelliJ IDEA

I installed it according to the instructions on the IntelliJ IDEA web site. I downloaded it to my Ubuntu laptop and installed it under /opt/intellij.

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 Restart IDE.

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 /home/chris/.local/bin/stack, but 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:

  1. Compile errors when changing code on the fly. Slow, but works. You can hit the "Haskell Problems" tab to see the actual compiler messages.
  2. Hitting Ctrl and mousing over something, which is how you get metadata in IDEA.
    1. Go to definition of library code.
    2. Go to definition of local code.
    3. Type info at point.
    4. 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 properly:

  1. You have to go "Create project from existing source"
  2. Choose "Create from external model"
  3. Choose the "Haskell" SDK.

Then it should be good to go. Other ways didn't work for me and I got stuck.

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 must-have.

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 installing the Haskero plugin, which, as I understand, is in spirit the same backend and functionality of IntelliJ-Haskell. It said "This extension is enabled globally".

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 edited my 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 it:

$ date
Wed 13 Nov 10:09:38 CET 2019
$ date
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 error in 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 github.com/haskell/haskell-ide-engine.

Apparently I have to manually install something. Okay, sure, why not?

There's 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:

Targets:
   [snip]
    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 2.4.1.0) 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
   [snip]

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.

SublimeText

Another popular editor is SublimeText. I installed it via the apt repository documented here. I decided to try the SublimeHaskell 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 UIs.

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 ghc-mod.

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 hsdev.yaml:

packages: []
resolver: lts-13.29
extra-deps:
- hsdev-0.3.3.1
- haddock-api-2.21.0
- hdocs-0.5.3.1
- network-3.0.1.1

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 Main.hs file.

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.

Summary

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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