add nix flake with devshell

.envrc

@@ -0,0 +1 @@
+use flake

.gitignore

@@ -26,3 +26,6 @@ xler-*.tar
 /.elixir_ls
 
 *.xls
+
+.direnv
+.state

flake.lock

@@ -0,0 +1,26 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1722062969,
+        "narHash": "sha256-QOS0ykELUmPbrrUGmegAUlpmUFznDQeR4q7rFhl8eQg=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "b73c2221a46c13557b1b3be9c2070cc42cf01eb3",
+        "type": "github"
+      },
+      "original": {
+        "id": "nixpkgs",
+        "ref": "nixos-unstable",
+        "type": "indirect"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,34 @@
+{
+  inputs = { nixpkgs.url = "nixpkgs/nixos-unstable"; };
+
+  outputs = { self, nixpkgs }: {
+    devShell.x86_64-linux = let
+      system = "x86_64-linux";
+      pkgs = import nixpkgs { inherit system; };
+      beam = pkgs.beam.packages.erlang_27;
+      elixir = beam.elixir_1_17;
+      elixir-ls = (beam.elixir-ls.override { inherit elixir; });
+    in pkgs.mkShell {
+      buildInputs = [
+        elixir
+        elixir-ls
+        pkgs.rustc
+        pkgs.cargo
+        pkgs.rust-analyzer
+        pkgs.rustfmt
+      ];
+      shellHook = ''
+        # this allows mix to work on the local directory
+        mkdir -p .state/mix .state/hex
+        export MIX_HOME=$PWD/.state/mix
+        export HEX_HOME=$PWD/.state/hex
+        export PATH=$MIX_HOME/bin:$MIX_HOME/escripts:$HEX_HOME/bin:$PATH
+        # TODO: not sure how to make hex available without installing it afterwards.
+        mix local.hex --if-missing --force
+        export LANG=en_US.UTF-8
+        export ERL_AFLAGS="-kernel shell_history enabled -kernel shell_history_path '\"$PWD/.state\"' -kernel shell_history_file_bytes 1024000"
+        export RUST_SRC_PATH="${pkgs.rustPlatform.rustLibSrc}"
+      '';
+    };
+  };
+}