Instantiate haskell template

.envrc

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+use flake

.gitignore

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+.pre-commit-config.yaml
+result
+.direnv

README.org

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+#+TITLE: FilePack - A library and tool to bundle up files
+
+* What is it?
+
+#+begin_quote
+Throughout this chapter, you’ll work through building a library for a tool called filepack. The FilePack library that we build will allow users to create archives of files that can be saved to disk, stored in a database, or sent over the internet. The examples you build as you work through this chapter will only support the programmatic creation and extraction of archives, but you are encouraged to create a complete application around this library as an additional example.
+#+end_quote

app/filepack.hs

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+module Main (main) where
+
+import FilePack (greet)
+
+main :: IO ()
+main = greet "Hello, World!"

filepack.cabal

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+cabal-version: 1.12
+
+-- This file has been generated from package.yaml by hpack version 0.34.7.
+--
+-- see: https://github.com/sol/hpack
+
+name:           filepack
+version:        0.0.1.0
+author:         Alexander Kobjolke
+maintainer:     alex@jakalx.net
+copyright:      Alexander Kobjolke 2022
+license:        MIT
+build-type:     Simple
+extra-source-files:
+    README.org
+
+library
+  exposed-modules:
+      FilePack
+  other-modules:
+      Paths_filepack
+  hs-source-dirs:
+      src
+  ghc-options: -Wall
+  build-depends:
+      base >=4.13 && <5
+  default-language: GHC2021
+
+executable filepack
+  main-is: filepack.hs
+  other-modules:
+      Paths_filepack
+  hs-source-dirs:
+      app
+  ghc-options: -Wall
+  build-depends:
+      base >=4.13 && <5
+    , filepack
+  default-language: GHC2021

flake.lock

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+{
+  "nodes": {
+    "flake-utils": {
+      "locked": {
+        "lastModified": 1659877975,
+        "narHash": "sha256-zllb8aq3YO3h8B/U0/J1WBgAL8EX5yWf5pMj3G0NAmc=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "c0e246b9b83f637f4681389ecabcb2681b4f3af0",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "flake-utils_2": {
+      "locked": {
+        "lastModified": 1644229661,
+        "narHash": "sha256-1YdnJAsNy69bpcjuoKdOYQX0YxZBiCYZo4Twxerqv7k=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "3cecb5b042f7f209c56ffd8371b2711a290ec797",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1661626419,
+        "narHash": "sha256-CjdPtdwH7I5Es4SjdCGuNfeulIyaM1LP0dXGWi4dyuQ=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "a5e05d62460ff0b7627559a8b55ab421041ebf0a",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "pre-commit-hooks": {
+      "inputs": {
+        "flake-utils": "flake-utils_2",
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1660830093,
+        "narHash": "sha256-HUhx3a82C7bgp2REdGFeHJdhEAzMGCk3V8xIvfBqg1I=",
+        "owner": "cachix",
+        "repo": "pre-commit-hooks.nix",
+        "rev": "8cb8ea5f1c7bc2984f460587fddd5f2e558f6eb8",
+        "type": "github"
+      },
+      "original": {
+        "owner": "cachix",
+        "repo": "pre-commit-hooks.nix",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs",
+        "pre-commit-hooks": "pre-commit-hooks"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

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+{
+  description = "Haskell Nix Template";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs";
+
+    flake-utils.url = "github:numtide/flake-utils";
+
+    pre-commit-hooks.url = "github:cachix/pre-commit-hooks.nix";
+    pre-commit-hooks.inputs.nixpkgs.follows = "nixpkgs";
+  };
+
+  outputs = { self, nixpkgs, flake-utils, pre-commit-hooks }:
+    flake-utils.lib.eachSystem [ "x86_64-linux" ] (system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+
+        overlay = final: prev: {
+          filepack = final.callCabal2nix "filepack" ./. { };
+        };
+
+        haskellPackages = pkgs.haskell.packages.ghc924.extend overlay;
+      in {
+        packages.default = haskellPackages.filepack;
+
+        apps = {
+          default = {
+            type = "app";
+            program = "${self.defaultPackage.${system}}/bin/hello";
+          };
+        };
+
+        checks = {
+          pre-commit-check = pre-commit-hooks.lib.${system}.run {
+            src = ./.;
+            settings = { ormolu.defaultExtensions = [ "GHC2021" ]; };
+            tools.fourmolu = haskellPackages.fourmolu;
+            hooks = {
+              nixfmt.enable = true;
+              fourmolu.enable = true;
+              hpack.enable = true;
+              hlint.enable = true;
+            };
+          };
+        };
+
+        devShells.default = haskellPackages.shellFor {
+          inherit (self.checks.${system}.pre-commit-check) shellHook;
+
+          packages = p: [ p.filepack ];
+
+          withHoogle = true;
+
+          nativeBuildInputs = with pkgs; [
+            haskellPackages.haskell-language-server
+            haskellPackages.fourmolu
+            haskellPackages.hspec-discover
+            haskellPackages.doctest
+            cabal-install
+            ghcid
+            nixfmt
+            hpack
+            hlint
+          ];
+        };
+      });
+}

package.yaml

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+name: filepack
+version: 0.0.1.0
+license: MIT
+author: "Alexander Kobjolke"
+maintainer: "alex@jakalx.net"
+copyright: "Alexander Kobjolke 2022"
+
+extra-source-files:
+  - README.org
+
+dependencies:
+  - base >= 4.13 && < 5
+
+ghc-options:
+  - -Wall
+
+library:
+  source-dirs: src
+  verbatim:
+    default-language: GHC2021
+
+executables:
+  filepack:
+    source-dirs: app
+    main: filepack.hs
+    dependencies:
+      - filepack
+    verbatim:
+      default-language: GHC2021

src/FilePack.hs

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+module FilePack (
+    greet,
+) where
+
+import Control.Monad.IO.Class (
+    MonadIO,
+    liftIO,
+ )
+
+greet :: MonadIO m => String -> m ()
+greet = liftIO <$> putStrLn