Installing/hacking Yi

Installing Yi

Yi requires GHC 7.8 at minimum and is mainly developed with GHC 7.10.1.

With the Haskell Platform installed, yi can be installed with cabal-install:

$ cabal update
$ cabal install yi

On Linux systems, you will need ncurses development headers for the Vty frontend. For example, Ubuntu requires libncurses5-dev for ncurses support and libicu-dev for unicode support.

The frontends for yi can be manually specified as follows:

$ cabal install yi -fvty -fpango

Options are -fvty and -fpango.

Note: If you get a frontend not found warning, install yi with the frontend manually specified by -fvty or -fpango while doing cabal install.

Note: If you’re having weird problems such as your changes not seeming to take effect, you might have some stale stuff in the cache directory which you should empty: on my system it’s ~/.cache/yi.

Note: If you use Stack, you can perform the equivalent of the above cabal commands with:

$ stack install yi


$ stack install yi --flag yi:vty --flag yi:pango

then start Yi using:

$ stack exec yi --package yi

Installing Yi from source

The Yi source tree is split into multiple packages such as yi-core, yi-language. These are all described in hpack files, from which there will be derived appropriate Cabal files during building.

Generally, Yi can be built using cabal or stack. For the stack users: Please note that stackage nightlies have recently been switched to GHC 8. Since older versions of stack might fail to build Yi using GHC 8 or do not automatically generate Cabal files, consider upgrading to a recent version of stack in case you encounter build problems.

Using Cabal-install

You can build and install Yi from source using Cabal-install as follows:

$ git clone
$ cd yi
$ cabal update
$ cabal install

If you are looking to get absolutely latest sources, make sure to install the supporting packages before installing Yi. Usually these packages are rarely updated and the version on Hackage is up-to-date. You can set up the supporting repositories from the GitHub project page.

Using Stack

Building and installing using stack should be similarly straightforward. After having cloned the repository and changed into its directory use the following commands:

$ stack build
$ stack install

Using a Cabal sandbox

Cabal-install 1.18 and higher support sandboxing which isolates the Yi installation from the rest of the cabal environment. This is especially important if you plan on hacking on Yi itself, or on libraries for Yi.

If your cabal version is lower than 1.20, you can install a newer version of cabal-install using cabal itself. This is recommended since newer versions of Cabal have several useful utilities for sandboxed environments.

$ cabal update
$ cabal install cabal-install
$ cabal --version

As Yi compiles your config file once you start it, the config needs to know where to look for any of its dependencies, such as Yi itself! If these are inside of the sandbox, it doesn’t know where to look and you’ll get config compilation errors due to missing modules.

To sandbox, navigate to your source yi directory. For me it’s ~/programming/yi/.

We then setup a cabal sandbox:

$ cd ~/programming/yi
$ cabal sandbox init
$ cabal install --only-dependencies
$ cabal install

From cabal-install 1.20, Yi can be launched in an environment using the sandbox’s package DB using cabal exec yi. It may be useful to create an alias or small script for this, along the lines of:

#!/usr/bin/env bash
env CABAL_SANDBOX_CONFIG=$YI_DIR/cabal.sandbox.config cabal exec $YI_DIR/dist/build/yi/yi -- "$@"

The "$@" part means that all the arguments we pass to this script are passed on to the Yi binary which means we can still use all the regular flags, such as yi --as=emacs. Of course, you’ll need to adjust the paths used to match your sandbox and package directories.

There’s one more thing to mention in this section, and that is config dependencies. One of the great things about Yi is that we have access to the wealth of existing Haskell libraries and we can take advantage of this in our config file. There are two scenarios:

  • If the package your config depends on is on Hackage and you want to use that, just use cabal install in the sandboxed Yi directory. So if your config depends on semigroups, you’d run cabal install semigroups. After doing this, semigroups should now be visible when your config is getting compiled.

  • If the package your config depends on is local, for example when you’re developing the library that you want to use or if you need a patched version, you’ll have to use cabal sandbox add-source command. As an example, I’m developing a yi-haskell-utils package and my config depends on it. To accommodate for this, I ran cabal sandbox add-source ~/programming/yi-haskell-utils. You can then cabal install yi-haskell-utils to add the package to the sandbox. You should call cabal build in the sandbox directory after you modify a local package so that the sandbox has an up-to-date version of the package.

I suspect that it’d be perfectly possible to make your config file into a cabal project and manage the dependencies that way but I have not yet investigated this approach.

Still doesn’t work? Try the older instructions such as those removed here or here. Make sure to let us know!

Installing Yi with Nix

If you’re interested in Hacking Yi with Nix, see the section on Hacking Yi with Nix. For simpler setups, you can use the Yi wrapper provided. You will need to edit your nix config file (usually ~/.nixpkgs/config.nix) to reflect the following:

{ pkgs }:

with pkgs;

  ghcCompiler = pkgs.haskell.packages.ghc7101;
  packageOverrides = super: let self = super.pkgs; in
    yi-custom = pkgs.yi.override {
      haskellPackages = ghcCompiler;
      extraPackages = p: with p; [ lens ];

where extraPackages is a list of haskell packages you wish to use in your Yi config, and haskellPackages is your haskell package set.

If you want to compile and install local version of certain haskell packages, within packageOverrides you could define a function as follows:

yi_packages = p: p.override {
  overrides = se : su : {
    yi = self.haskellPackages.callPackage /home/siddhu/Documents/code/yi {};
    yi-language = self.haskellPackages.callPackage /home/siddhu/Documents/code/yi-language {};

and replace haskellPackages = ghcCompiler with haskellPackages = yi_packages ghcCompiler.

If the above doesn’t work, or if you only need to test Yi once, you could manually set $NIX_GHC to point to your existing haskellpackages by running the following in the terminal:

$ nix-shell -p yi
$ export NIX_GHC=$(which ghc)
$ yi

Hacking Yi with nix

Hacking Yi with nix is pretty easy. Forget about cabal sanboxes and other nastiness. You will first need a way to override the Haskell package set. I will not go into this here, see NixOS wiki and other associated resources for help.

Once you have done this, you’ll need project files for each repository Yi depends on, as seen in its cabal file and from the repos here.

I’ll first discuss setting up the supporting repos and then move onto the main repository. The supporting repos don’t need anything unusual, make project files and stick them in your overrides as always.

Setting up supporting repositiories

For each repository, you’ll need default.nix and most likely shell.nix too if you want to do hacking in it. Consider yi-rope repository as an example.

Check out yi-rope from git into somewhere. Generate default.nix with cabal2nix and stash it somewhere accessible. Add shell.nix in the same directory, with the trivial contents:

let pkgs = import <nixpkgs> {};
    myHaskellPackages = pkgs.myHaskellPackages;
    haskellPackages = myHaskellPackages.override {
      extension = self: super: {
        yiRope = myHaskellPackages.callPackage ./. {};
in pkgs.lib.overrideDerivation haskellPackages.yiRope (attrs: {
  noHaddock = true;
  buildInputs = [ ] ++ attrs.buildInputs;

myHaskellPackages is my overriden package set. noHaddock = true so that hacking is not slow inside nix-shell. You can add extra tools you like to use to the buildInputs list.

Symlink your default.nix and shell.nix from within your yi-rope checkout and ignore them in git (locally, not in .gitignore)

[shana@lenalee:~/programming/yi]$ l ~/programming/yi-rope
total 168K
drwxr-xr-x   6 shana shana   4.0K Sep 29 06:59 .
drwxr-xr-x 199 shana shana   4.0K Oct  5 18:36 ..
lrwxrwxrwx   1 shana shana     64 Sep  6 06:59 default.nix -> /home/shana/programming/nix-project-defaults/yi-rope/default.nix
lrwxrwxrwx   1 shana shana     62 Sep  6 06:58 shell.nix -> /home/shana/programming/nix-project-defaults/yi-rope/shell.nix

Then stick it into your Haskell overrides. Currently my overrides for Yi repos look as follows:

wordTrie          = normalPackageS se "word-trie";
ooPrototypes      = normalPackageS se "oo-prototypes";
yiLanguage        = normalPackageS se "yi-language";
yiRope            = normalPackageS se "yi-rope";
dynamicState      = normalPackageS se "dynamic-state";

where normalPackageS is just a handy alias for callPackage. See my setup for details. Hack on these as you would with any normal project.

Setting up main repository

Now for the main repository. The tricky bit is that Yi needs to be able to find its packages and its dependencies at runtime so that running the GHCi evaluator (M-x) works. First generate default.nix and use a stock shell.nix as usual. You might want to manually add vty to dependency list and set

  configureFlags = [ "-fpango" "-fvty" ];

  noHaddock = self.ghc.version == "7.6.3";

Symlink the project files as usual. The generated default.nix should have all the supporting repositories listed so nix-shell --pure should just work: remember to add the repos to your Haskell package set.

Once you’re in the shell, the first thing you want to do is eval "$configurePhase" && eval "$buildPhase": this will fully build Yi once which has the side effect of generating all the CPP macros and cabal-generated files. It also has the effect of setting GHC_PACKAGE_PATH which is useful later.

You should now be able to simply use ghci on any file in the repository: .ghci is already set up to pick everything up.

Once you’re done making changes, you probably want to run Yi and try them out. Run eval "$buildPhase" to build Yi. You can run the tests with eval "$checkPhase".

Now to run it, use something like

[nix-shell:~/programming/yi/yi]$ GHC_PACKAGE_PATH="$(pwd)/dist/package.conf.inplace:$GHC_PACKAGE_PATH" TERM=xterm yi_datadir=. dist/build/yi/yi -y /tmp -fpango --as=emacs /tmp/T.hs

Here’s what happens: we set GHC_PACKAGE_PATH to the generated Yi package config inside dist (this allows us to find Yi modules) and the rest of packages (this allows to find all the dependencies). The reason for $(pwd)/… rather than a relative path is to keep this working after we M-x cd inside the editor. We set TERM which you might need depending on your terminal due to nix-shell messing with some env vars to ensure purity. We also set yi_datadir to the current directory so that Yi can finds its icon and such.

Once all those are set, we run the compiled Yi itself (dist/build/yi/yi), point it somewhere away from the user config directory (-y /tmp), choose the frontend (-fpango), choose the keymap (--as=emacs) and choose the file to open (/tmp/T.hs). This should succesfully start up Yi and ensure M-x and all such dynamic commands work. All in all, this gives you an environment allowing you to hack Yi with nix-shell as always even though it’s spread across multiple repositories and has an unusual setup.

Actually installing Yi with nix along with user config is a bit out of scope of this section but it works similarly, wrapping the binary into a script which sets GHC_PACKAGE_PATH.

Automatic version tracking

Here’s an extra bit: manually tracking changing versions of the subrepositories can get pretty boring, pretty quickly. You can however use nix to automatically read the version from the cabal file and create the derivation based on the result. It ends up a bit ugly but it works. For yi-rope my default.nix is therefore

{ cabal, binary, deepseq, fingertree, hspec, QuickCheck
, quickcheckInstances, text, criterion

let pkgs = import <nixpkgs> {};
    lib = pkgs.lib;
    sr  = "/home/shana/programming/yi-rope";
    file = builtins.readFile (sr + "/yi-rope.cabal");
    strs = lib.strings.splitString "\n" file;
    vstr = builtins.head (builtins.filter (s: lib.strings.hasPrefix "version:" s) strs);
    vrsn = lib.strings.removePrefix "version:" (lib.strings.replaceChars [" "] [""] vstr);

cabal.mkDerivation (self: {
  pname = "yi-rope";
  version = vrsn;
  src = sr;
  buildDepends = [ binary deepseq fingertree text criterion ];
  testDepends = [ hspec QuickCheck quickcheckInstances text ];
  meta = {
    description = "A rope data structure used by Yi";
    license = self.stdenv.lib.licenses.gpl3;
    platforms = self.ghc.meta.platforms;

The downside is if you ever run cabal2nix over it, this scheme will get clobbered so it’s mostly only useful for the repositories which will most likely not get many extra dependencies but are likely to change versions often.

Installing Yi on MacOS

If you’re seeing an error like the following:

cabal: Error: some packages failed to install:
text-icu- failed during the configure step. The exception was:
ExitFailure 1

First make sure that the icu library is installed on the system:

$ brew install icu4c

Yi might not be able to find the icu library on MacOS unless the lib and include paths are explicitly passed as arguments to cabal.

$ cabal install text-icu --extra-lib-dirs=/usr/local/opt/icu4c/lib --extra-include-dirs=/usr/local/opt/icu4c/include
$ cabal install yi --extra-lib-dirs=/usr/local/opt/icu4c/lib --extra-include-dirs=/usr/local/opt/icu4c/include

Or if you prefer stack instead:

$ stack install text-icu --extra-lib-dirs=/usr/local/opt/icu4c/lib --extra-include-dirs=/usr/local/opt/icu4c/include
$ stack install yi