Basic nix haskell setup

init-haskell.sh

#!/usr/bin/env bash
set -Eeuxo pipefail

type git >/dev/null 2>&1 || { echo >&2 "I require git but it's not installed.  Aborting."; exit 1; }
type nix >/dev/null 2>&1 || { echo >&2 "I require nix but it's not installed.  Aborting."; exit 1; }
type niv >/dev/null 2>&1 || { echo >&2 "I require niv but it's not installed.  Aborting."; exit 1; }
type direnv >/dev/null 2>&1 || { echo >&2 "I require direnv but it's not installed.  Aborting."; exit 1; }
type lorri >/dev/null 2>&1 || { echo >&2 "I require lorri but it's not installed.  Aborting."; exit 1; }

git init # initialize git repository
git ignore haskell > .gitignore # create gitignore file from haskell template
echo '*.cabal' >> .gitignore # cabal file doesn't need to be committed

export GITHUB_TOKEN=${gpg2 -q --for-your-eyes-only --no-tty -d $PASSWORD_STORE_DIR/services/github-token.gpg}

niv init # initialize niv
niv drop nixpkgs # we're going to be pinning nixpkgs anyway
niv add -n ghcide-nix cachix/ghcide-nix
niv add -n iohk-nixpkgs input-output-hk/nixpkgs
niv add -n iohk-hnix input-output-hk/haskell.nix

export author="Patrick D. Elliott"
export email="patrick.d.elliott@gmail.com"
export ghc="ghc883"
export projectname=${PWD##*/}

# Create hpack project
cat <<EOF > ./package.yaml
spec-version: 0.30.0
name: $projectname
author: ${author}
maintainer: ${email}
license: MIT

build-type: Simple

source-dirs: src
dependencies:
- { name: "base", version: '>=4.12 && <4.13' }

ghc-options: -Wall
library: {}
executable:
  main: Main.hs
EOF

mkdir src

cat <<EOF > ./src/Main.hs
module Main where

main :: IO ()
main = putStrLn "Hello, Haskell!"
EOF

cat <<EOF > ./hie.yaml
cradle: { cabal: {} }
EOF

# Add default.nix
cat <<EOF > ./default.nix
let
  haskellCompiler = "${ghc}";
  sources = import ./nix/sources.nix;
  ghcide = (import sources.ghcide-nix {})."ghcide-\${haskellCompiler}";
  haskellNix = import sources.iohk-hnix {};
  nixpkgsSrc = haskellNix.sources.nixpkgs-2003;
  nixpkgsArgs = haskellNix.nixpkgsArgs;
  pkgs = import nixpkgsSrc nixpkgsArgs;

  hspkgs = pkgs.haskell-nix.cabalProject {
    src = pkgs.haskell-nix.haskellLib.cleanGit { name = "${projectname}"; src = ./.; };
    compiler-nix-name = "\${haskellCompiler}";
  };

  shell = hspkgs.shellFor {
    withHoogle = true;
    buildInputs = [
      pkgs.cabal-install
      pkgs.haskellPackages.ghcid
      pkgs.haskellPackages.hpack
      pkgs.haskellPackages.brittany
      ghcide
    ];
  };
in
{
  inherit shell;
  inherit hspkgs;
  ${projectname} = hspkgs.${projectname};
}
EOF

cat << EOF > ./shell.nix
(import ./default.nix).shell
EOF

# Create direnv file
cat << 'EOF' > .envrc
eval "\$(lorri direnv)"
EOF

cat << 'EOF' > CACHES.md
This project uses various nix expressions for building code. In order to avoid building a huge amount of stuff at once, you might want to enable the following [cachix](https://cachix.org/) caches:

- ghcide-nix
- iohk

EOF

git add .