Long story short, I'd like some guidance on what's the (best) way to have Haskell work on Archlinux.
By work I mean all, in terms of the ghci command line tool, installing packages I don't have - such as vector-space, which this answer to a question of mine refers to -, and any other thing that could be necessary to a Haskell obstinate learner.
Archlinux wikipage on Haskell lists three (alternative?) packages for making Haskell work on the system, namely ghc, cabal-install, and stack. I have the first and the third installed on my system, but I think I must have installed the latter later (unless it's a dependency to ghc) while tampering around (probably in relation to Vim as a Haskell IDE). Furthermore, I have a huge amount of haskell-* packages installed (why? Who knows? As a learner I must have come multiple times to the point of say uh, let's try this!).
Are there any pros and cons ("cons", ahah) about each of those packages?
Can they all be used with/without conflicts?
Does any of them make any other superfluous?
Is there anything else I should be aware of which I seem apparently ignorant about based of what I've written?
Arch Linux's choice of providing dynamically linked libraries in their packages tends to get in the way if you are looking to develop Haskell code. As an Arch user myself, my default advice would be to not use Arch's Haskell packages at all, and instead to install whatever you need through ghcup or Stack, starting from the guidance in their respective project pages.
You are basically there. Try the following:
ghci: If you get the Haskell REPL then it works.
stack ghci: Again you should get the Haskell REPL. There are a lot of versions of GHC, and stack manages these along with the libraries. Whenever you use a new version of GHC stack will download it and create a local installation for you.
stack is independent of your Linux package manager. The trouble is that your distro will only have the Haskell libraries it actually needs for any applications it has integrated, and once you step outside of those you are in dependency hell with no support. So I recommend that you avoid your distro Haskell packages. stack does everything you need.
If you installed stack from your Linux package manager then you might want to uninstall it and use a personal copy (i.e. in your ~/.local directory) instead. Then you can always say stack update to check you have the latest version.
Once you have stack going, create a project by saying stack new my-project simple. Then go into the project folder and start editing. You can work with just a .hs file and GHC if you really want, but its painful; you will do much better with stack, even if you are just messing around.
You'll also need an editor. Basic functionality like syntax highlighting is available in pretty much everything, but once you get past Towers of Hanoi you are going to want something better. I use Atom with ide-haskell-ghcide. This uses the Haskell Language Server under the hood, so you will need to install that too. I know a bunch of other editors have HLS support, but I don't have experience with them.
Related
I don't get the point about Stack.
I used to write my Haskell code in my favourite environment, ran or compiled using GHC(i), and if necessary, installed packages using Cabal. Now, that apparently is not the way to go any more, but I don't understand how to work with Stack. So far, I have only understood that I need to write stack exec ghci instead ghci to start a repl.
Apart from that, the docs always talk about 'projects' for which I have to write some yaml files. But I probably don't have any project -- I just want to launch a GHCi repl and experiment a bit with my ideas. At the moment, this fails with the unability to get the packages that I want to work with installed.
How is working with Stack meant? Is there any explanation of their use cases? Where do I find my use case in there?
Edit. My confusion comes from the fact that I want to work with some software (IHaskell) whose installation guide explains the installation via stack. Assuming I already have a GHCi installed whose package base I maintain e.g. using Cabal. How would I have to set up stack.yaml to make stack use my global GHCi for that project?
First, notice that stack will use its own package base independent from cabal. AFAIK they can't be shared... hence, if you run stack build it'll download packages (including the compiler) on its own package database.
Nevertheless stack allows to use a system compiler (but not other libraries). To do so, in the stack.yaml you must have the following two lines
resolver: lts-XX.XX -- keep reading below
system-ghc: True
The version of the stackage snapshot can be found in: https://www.stackage.org/. Each snapshot works with a different version of the compiler. Be sure to use a snapshot with the same compiler version you have in you system. If it happens your system ghc is greater than any lts, then you can set allow-newer: true in stack.yaml.
Now, if getting a different database from stack feels wrong to you, notice that you can build the project with cabal too, since stack at the end of the day spits out a cabal file. Probably, It wont work out of the box if you build with cabal. You can modify the cabal file to match exactly the version of the packages of the snapshot you are using
In summary:
You can use your system-wide ghc
you can not share libraries installed with cabal.
you can use cabal to build the project, probably modifying the ihaskell.cabal file to match versions of the stackage's snapshot.
I have on my computer (macOS High Sierra) multiple installations of the standard (Glasgow) Haskell compiler. The oldest one (as far as I can remember) is a minimal installation, while I obtained the most recent version form the "Platform" installer, something like five or six months ago. I'm trying to get rid of the whole ecosystem (ghc, stack, cabal, and friends), mostly because I don't know what tools I will be using in the case I'll plan to get back using the language.
So my questions are:
Where does the minimal/"Platform" installer installs Haskell and all related stuff?
How can one remove the whole Haskell language and all its components mentioned above (in the case of a "Platform" install, and even in the case of a minimal installation)?
EDIT: I've just remembered of the uninstall-hs command (see also here), should I run this instead of removing files manually?
I think I have come up with a solution and I'll answer the latter question first:
All the details I was looking for (what effectively is installed after launching the minimal / "Platform" installer, and, most importantly, where these guys were placed) can be found in the documentation welcome file at /Library/Haskell/Doc/Start.html. More precisely:
On Mac OS X, the Haskell Platform is installed in two major pieces: GHC and Haskell Platform. They are installed respectively in: /Library/Frameworks/GHC.framework and /Library/Haskell. Executables are symlinked in /usr/local/bin [...].
There are also another two or three directories in the home folder, namely ~/.ghc and ~/.stack.
As said in the OP, the script uninstall-hs done its work, showing a (at least I hope so) comprehensive list of all the files that constitutes the Haskell "sdk" actually installed.
Feel free to post your answers, I hope this post will be useful to the community.
I'd like to have a simple way of ensuring that the packages in my system, whether they are in the global or the user package database, correspond to the versions in the current LTS Haskell.
I gather that there are fairly simple ways to do something like this for a specific project. But it's not clear to me how to achieve this for my Haskell system as a whole. I have Stack installed already (using Cabal), and use Homebrew where I can (e.g., for Haskell, just for cabal-install). I'm tempted by haskell-stack, but it's unclear what exactly that does.
Is there a simple way to ensure that my system's Haskell packages (wherever they reside) match LTS Haskell?
If you're using cabal-install, your best bet is to append the contents of https://www.stackage.org/lts-3.8/cabal.config?global=true (adjust the LTS snapshot slug to your preference) to your ~/.cabal/config. I'd caution against doing this, though, since you may well want to use different snapshots for different projects. Use of sandboxes with cabal-install is highly recommended (in fact, I set require-sandbox: true in my cabal config to make sure I don't forget).
For Stack, the LTS snapshot is always project-specific; there is no global setting. But setting the resolver: value in ~/.stack/global/stack.yaml sets it for when you run stack outside of a specific project, and also influences the choice of resolver for new projects (when you use stack init or stack new).
BTW, it looks like the Homebrew haskell-stack formula is just an alternate way to install Stack, so if you already have Stack there's no need to use it.
I recently finished the book "learnyouahaskell" and now I would like to apply my acquired knowledge by building a yesod application.
However I am not sure about how to get started.
There seems to be two options on how to set up a yesod project. One is with Stack, and the other is with cabal sandboxes.
But what are the differences (If any?) and the similarities between them? Does one count as best practice whereas the other doesn't?
The yesod quickstart suggests using stack, is this fine or should I use cabal sanbox?
There are actually three different packages that are being talked about here.
cabal-install is the current stable binary to build your applications.
stack was just released to the public recently. I believe it is trying to replace cabal-install as a better, more convenient tool. At the very least, it is showing the Haskell community a different way of something things.
Cabal is the library that both cabal-install and stack are based off of.
As for the differences between the first two tools.
cabal-install is a mature application used nearly everywhere within the Haskell community (at least in open source, I have no idea what people are doing behind closed doors).
stack is still a new (at least to the public) application used in some newer projects. Some more information can be found here. But some of the highlights are:
running stack build in a projects directory will install GHC (Haskell compiler) as well as the needed dependencies for the project.
stack, by default, runs off of stackage. Which is a curated version of hackage. Meaning you can expect the different packages to play nicely with each other. Leading to reproducible builds.
You can still fall back on hackage should you choose to.
The great thing about these two applications is that they can be used by different people for the same project. If you decide you want to use cabal-install with sandboxes, and someone comes along and wants to help with your project, they can just add the files that stack needs and they can use stack while you continue to use cabal-install. Or vice-versa.
here is one persons experience after using stack for the first time. They claim that it is a little bit easier to get started because there are a couple less steps required to get started. If nothing else, people highlight the pros and cons of each tool.
Note: I'm still fairly new to Haskell, and have never actually used stack. I've actually been told to stay away from it unless building something in yesod.
Edit: As stated in a comment under this answer, I believe I have mis-represented what people have told me about stack. The comments people have given me when I asked if I should switch over to stack were more along the lines of, If you are comfortable enough using cabal sandboxes, there is no reason to switch over to stack unless you are having issues.
The lead developer of Yesod (Michael Snoyman) is actively involved with the Stack tool. So, I would recommend you to set up Yesod with Stack. Also, Yesod has a quite a complex set of dependencies and using Stackage as the default curated source, helps very much in the installation process (which Stack takes care of by default).
Also read this post for understanding the differences of Stack from cabal.
I have the Haskell Platform 2012.4 installed on Windows. I would like to try the new extensions in GHC 7.6.2. It looks like the GHC 7.6.2 x86_64 download does not include an installer and is just the binaries. What is the proper way to get the latest version installed and set as the default for building Haskell projects? Thanks.
If you download GHC itself, you just get GHC and a tiny handful of libraries. If you download the Haskell Platform, you get GHC plus a much bigger collection of libraries. However, the Haskell Platform is updated infrequently, so you'll get an older version of GHC.
If you're asking "how do I install the Haskell Platform and then make it work with a newer GHC?", then the answer is "you don't". Haskell libraries have to be compiled for the specific version of GHC you're using.
You basically have two options:
Use the Haskell Platform, together with the version of GHC that it supplies.
Use the latest GHC, and compile whatever libraries you want manually.
On Linux it's not too bad, but Haskell libraries that bind to external C code tend to be fiddly to build on Windows. (Stuff like OpenGL, zlib, etc.) Packages that are 100% vanilla Haskell code are drop-dead easy to compile on any system.
I haven't done this and I'm at work so I can't test it out, but looking at the GHC docs I would think you can use the --with-compiler=path flag to select which version of GHC to use?
See also this question, related to using cabal with multiple versions of ghc installed. I would guess that you probably want to use cabal-dev or something to sandbox this, otherwise your package database may become a mess.
EDIT: As far as a default, I think you can set that in a cabal configuration file. See the comments to the accepted answer in that question I linked.
The other answers here are great, and I wanted to add that the current best way to get the latest version of GHC installed is to look at haskell.org's installation instructions. I bounced between lots of different options before I landed there, and I think it's the best source of truth from what I can tell.
To summarize the current instructions: if you already have chocolately set up, "at an elevated command prompt, run choco install haskell-dev, followed by refreshenv."