botiut/stack-arm.org

#+title: Installing stack on ARM bit
#+author: Annwan
#+date: 2022:03:04
#+options: h:1 num:nil toc:nil

** Why stack on ARM

People might want to run Haskell applications on ARM devices like a
Raspberry Pi. The Haskell compiler has supported the architecture
through LLVM for a couple of year now, as well as the builtin dependency
manager, Cabal. However the dependency management of Cabal is
system-wide (or at least user wide) and, because all packages interact
with each other, it can pose problems with compatibility.

That is the problem that =stack= solves by allowing for reproducible,
isolated environment for each project, and a lot of projects now use
stack for their dependency and version management.

However stack does not provide any build for arm systems, we thus need
to install it another way


** First step, getting a compiler

Whereas =stack= does not provide an ARM build, GHC does. so we first
head to the [[https://www.haskell.org/ghc/][GHC download page]] and get the latest build. Usually the
archive is for Debian, but should work for any GNU libc based 
distribution.
#+begin_quote
At time of writing stack lts snapshots don't use GHC 9 yet so the used
version is 8.10.7.
#+end_quote
This should leave you with an archive like
=ghc-8.10.7-aarch64-deb10-linux.tar.xz= (Keep that archive around, we
will need it for stack later on).

We are now going to extract and setup a minimal Haskell environment

#+begin_src shell
tar xvf ghc-8.10.7-aarch64-deb10-linux.tar.xz
cd ghc-8.10.7
./configure --prefix=$HOME/.cabal
make install
#+end_src

Next grab the latest cabal binary for AArch64 from [[https://www.haskell.org/cabal/download.html][Cabal download page]]
(usually tagged as for Debian but should work on any GNU Libc system).
Put the contained executable in =$HOME/.cabal/bin=

Finally put =$HOME/.cabal/bin= in your PATH.

You now have a minimal Haskell installation in your path, we are now
ready to move to the next step

** Install a stack bootstrap environment

Now that we can compile some Haskell things, lets install a bootstrap
stack installation. It is not the final one, because this one is tied to
a cabal version instead of a stack snapshot

To do that we simply tell cabal to install stack

#+begin_src shell 
cabal install stack
#+end_src

This compilation will take a bunch of memory, and most likely a while, if
on a system with limited RAM, you might want to unmout the tmpfs at
=/tmp= and increase the swap size in order to have around 4GB free

** Register the compiler with stack

Remember when I said to keep the GHC archive around because we will need
it later, well that later is now. Move that archive to a folder where
you'll most likely not accidentally delete it, here I'll use =~/ghc=

Once the archive is stored in that folder, open your stack configuration
(=~/.stack/config.yaml=) and add the following

#+begin_src yaml 
setup-info:
  ghc:
    linux-aarch64-tinfo6:
      8.10.7:
        url: "~/ghc/ghc-8.10.7-aarch64-deb10-linux.tar.xz"
#+end_src

** Finaly, bootstrap stack with itself

Now we need to reinstall stack with itself, to untie it from the
temporary setup.

#+begin_src shell
stack setup
stack install stack
#+end_src

Once again this will take a lot of both memory and time.

** Clean up

You can now remove the =~/.cabal/bin= folder and add the =~/.local/bin=
folder to the path, that is where stack will install binaries.

You can also delete the =~/.cabal= as it is no longer needed

Once this is done, you now have a fully functionnal stack setup.

If in the future you need an additionnal compiler version you can add
its archive to the compilers folder and register it with stack the same
way as previously done.