Add a nix flake setup

.envrc

@@ -0,0 +1,6 @@
+use_flake() {
+  watch_file flake.nix
+  watch_file flake.lock
+  eval "$(nix print-dev-env)"
+}
+use flake

.github/workflows/nix.yml

@@ -0,0 +1,24 @@
+name: "Nix flakes CI"
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/[email protected]
+    - uses: cachix/install-nix-action@v13
+      with:
+        install_url: https://nixos-nix-install-tests.cachix.org/serve/i6laym9jw3wg9mw6ncyrk6gjx4l34vvx/install
+        install_options: '--tarball-url-prefix https://nixos-nix-install-tests.cachix.org/serve'
+        extra_nix_config: |
+          experimental-features = nix-command flakes
+          access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
+    - uses: cachix/cachix-action@v10
+      with:
+        name: yatima
+        authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+    - run: nix build
+    - run: nix flake check

.gitignore

@@ -1 +1,2 @@
 /build
+result*

flake.nix

@@ -0,0 +1,52 @@
+{
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-21.05";
+    lean = {
+      url = "github:leanprover/lean4";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+    flake-utils = {
+      url = "github:numtide/flake-utils";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+  };
+
+  outputs =
+    { self
+    , flake-utils
+    , nixpkgs
+    , lean
+    }:
+    flake-utils.lib.eachDefaultSystem (system:
+    let
+      pkgs = import nixpkgs { inherit system; };
+      packageName = "Lake";
+      src = ./.;
+      leanPkgs = lean.packages.${system};
+      inherit (leanPkgs) leanc stage1;
+      inherit (pkgs.lib) concatStrings debug;
+      project = leanPkgs.buildLeanPackage {
+        name = packageName;
+        inherit src;
+      };
+    in
+    {
+      packages.${packageName} = project.lean-package;
+
+      defaultPackage = self.packages.${system}.${packageName};
+
+      apps.lake = flake-utils.lib.mkApp {
+        name = "lake";
+        drv = project.executable;
+      };
+
+      defaultApp = self.apps.${system}.lake;
+
+      # `nix develop`
+      devShell = pkgs.mkShell {
+        buildInputs = with pkgs; [
+          lean-pkgs.lean
+        ];
+      };
+    });
+}