Add initial flake

flake.nix

@@ -0,0 +1,69 @@
+{
+  inputs = {
+    nixpkgs = {
+      url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    };
+    utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs =
+    inputs:
+    inputs.utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = import inputs.nixpkgs {
+          localSystem = system;
+          overlays = [
+            (final: prev: {
+
+              riscv-bluespec-classic = pkgs.callPackage (
+                {
+                  stdenv,
+                  bluespec,
+                  nextpnr,
+                  openfpgaloader,
+                  trellis,
+                  which,
+                  yosys,
+                  TOPMODULE ? "mkTop",
+                  makeFlags ? [ ],
+                }:
+                stdenv.mkDerivation {
+                  pname = "riscv-bluespec-classic";
+                  version = "0.1.0";
+                  src = ./.;
+
+                  # Versions can be checked with
+                  # `nix eval --json ".#bluespec-joh-template.nativeBuildInputs" | nix-shell -p jq --run jq`
+                  nativeBuildInputs = [
+                    bluespec
+                    nextpnr
+                    openfpgaloader
+                    trellis
+                    which
+                    yosys
+                  ];
+
+                  # TODO: Build and install something
+
+                }
+              ) { };
+
+            })
+          ];
+        };
+      in
+      {
+        packages = {
+          default = inputs.self.packages."${system}".riscv-bluespec-classic;
+          riscv-bluespec-classic = pkgs.riscv-bluespec-classic;
+        };
+
+        devShells.default =
+          with pkgs;
+          mkShell {
+            inputsFrom = [ riscv-bluespec-classic ];
+          };
+      }
+    );
+}