Merge pull request #70 from mattjbray/dave/add-flake

Add simple flake for opam/ocamlformat

flake.nix

@@ -0,0 +1,37 @@
+{
+  inputs = {
+    nixpkgs.url = "nixpkgs/nixpkgs-unstable";
+
+    #ocamlformat 0.22.4 is a bit old, so is only in older versions of nixpkgs
+    nixpkgs2305.url = "nixpkgs/nixos-23.05";
+
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, nixpkgs2305, flake-utils }@attrs:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+        pkgs2305 = nixpkgs2305.legacyPackages.${system};
+      in
+      {
+        # for use by nix fmt
+        formatter = pkgs.nixpkgs-fmt;
+
+        devShells.default =
+          pkgs.mkShell {
+            buildInputs =
+              (if pkgs.stdenv.isDarwin then
+                (with pkgs.darwin.apple_sdk.frameworks; [ CoreServices Foundation ])
+
+              else
+                [ pkgs.inotify-tools ]) ++ [
+                pkgs.opam
+                pkgs2305.ocamlformat_0_20_1
+                #pkgs.pkg-config
+              ]
+            ;
+          };
+
+      });
+}