GHCJS with Nix on WINDOWS

ghcjs.md

1. Prerequisites

• Install Docker for Windows
• Change docker settings
  • Increase RAM
  • Enable shared drive

2. Start a nix shell with docker

• Create a new folder and open a terminal inside it
• Start a docker container with interactive shell, forwarding port 6400 for GHCJSi:

docker run -p 6400:6400 -it -v <local path>:/project -w /project lnl7/nix:2018-01-13 bash

3. Create project and nix files

• Run nix-env -i cabal-install cabal2nix ghc
  • Installs cabal, cabal2nix and ghc using nix
• Run cabal update && cabal init
  • Initialise cabal and create a new project
• Run cabal2nix . > default.nix
  • This creates a nix derivation with dependencies based on the .cabal file
  • Run this again when the dependencies in the .cabal file have changed

3. Create project and nix files

• Create a release.nix with the following content:

 let
   bootstrap = import <nixpkgs> { };
 
   nixpkgs = builtins.fromJSON (builtins.readFile ./nixpkgs.json);
 
   src = bootstrap.fetchFromGitHub {
     owner = "NixOS";
     repo  = "nixpkgs";
     inherit (nixpkgs) rev sha256;
   };
 
   pkgs = import src { };
 in
 {
   project = pkgs.haskell.packages.ghcjsHEAD.callPackage ./default.nix { };
 }

• This pins the version of 'nixpkgs' to the one specified in nixpkgs.json (next slide)

3. Create project and nix files

..and a nixpkgs.json with

  {
    "url": "https://github.com/NixOS/nixpkgs.git",
    "rev": "fcc8cae88d5429ae2693b03e870dfc4fe6a1c6bf",
    "date": "2018-01-20T15:47:59-05:00",
    "sha256": "0bpzwiyam6a68wp8bizlkdsazdfq2xyfwa7wjaydf8ps64avr23p",
    "fetchSubmodules": true
  }

• We need to use fcc8cae or newer to get a working build of GHCJS
• This file was created with nix-prefetch-git

4. Open a shell with GHCJS

• nix-shell --attr project.env release.nix
  • Brings all packages into scope
• cabal new-configure -O0 --ghcjs
• cabal new-build