Create nix flake to ensure reproducibility

.github/workflows/nix.yml

@@ -16,5 +16,5 @@ jobs:
     - uses: cachix/install-nix-action@daddc62a2e67d1decb56e028c9fa68344b9b7c2a
       with:
         nix_path: nixpkgs=channel:nixos-23.05
-    - run: nix-build shell.nix
-    - run: nix-shell --run "hlint src && fix-hie && git diff --exit-code hie.yaml"
+    - run: nix build
+    - run: nix develop --command bash -c "hlint src && fix-hie && git diff --exit-code hie.yaml"

README.md

@@ -8,31 +8,37 @@ This version of MarloweScan requires a running instance of the Marlowe Runtime.
 
 ## Using Nix
 
-This repo provides a `shell.nix` file that can be used for developing and building MarloweScan without having to worry about dependencies.
+This repo provides a `flake.nix` file that can be used for developing and building MarloweScan without having to worry about dependencies.
 
 ### Building with Nix
 
-To build MarloweScan with Nix, you can use the `nix-build` command with `shell.nix`:
+To build MarloweScan with Nix, you can use the `nix` command:
 
 ```bash
-nix-build shell.nix
+nix build
 ```
 
 The resulting executable will be made available in `result/bin/marlowe-scan-exe`
 
+Alternatively, you can run MarloweScan directly by writing:
+
+```bash
+nix run
+```
+
 ### Development shell
 
-As usual, you can use the `nix-shell` command to enter the development environment from the root folder of the project:
+As usual, you can use the `nix` command to enter the development environment from the root folder of the project:
 
 ```bash
-nix-shell
+nix develop
 ```
 
-That will make the required Haskell libraries, tools like cabal, stack, the Haskell Language Server, and the `gen-hie` command available in the command line.
+That will make the required Haskell libraries, tools like cabal, stack, the Haskell Language Server, and the `fix-hie` command available in the command line.
 
 ### Caching dependencies
 
-In order to take advantage of caching, you can use the `https://nixos.org/channels/nixos-22.11` channel. If using a different channel like `unstable`, building may take a while.
+In order to take advantage of caching, you can use the `https://nixos.org/channels/nixos-23.05` channel.
 
 ## Using Stack
 

flake.nix

@@ -0,0 +1,17 @@
+{
+  description = "MarloweScan - An explorer for Marlowe contracts";
+
+  inputs.nixpkgs.url = github:NixOS/nixpkgs/23.05;
+
+  outputs = { self, nixpkgs }: {
+    defaultPackage.x86_64-linux =
+      with import nixpkgs { system = "x86_64-linux"; };
+      with haskellPackages;
+      import ./shell.nix { nixpkgs = nixpkgs; haskellPackages = haskellPackages; };
+    devShells.x86_64-linux.default =
+      with import nixpkgs { system = "x86_64-linux"; };
+      with haskellPackages;
+      (import ./shell.nix { nixpkgs = nixpkgs; haskellPackages = haskellPackages; }).env;
+ };
+
+}

shell.nix

@@ -1,4 +1,4 @@
-{ nixpkgs ? import <nixpkgs> {}, compiler ? "ghc92", doBenchmark ? false }:
+{ nixpkgs ? import <nixpkgs> {}, haskellPackages ? (import <nixpkgs> {}).haskellPackages }:
 
 let
   pkgs = nixpkgs;
@@ -29,14 +29,5 @@ let
           }
         '';
       };
-  haskellPackages = if compiler == "default"
-                       then pkgs.haskellPackages
-                       else pkgs.haskell.packages.${compiler};
-
-  variant = if doBenchmark then pkgs.haskell.lib.doBenchmark else pkgs.lib.id;
-
-  drv = variant (haskellPackages.callPackage f {});
-
-in
-
-  if pkgs.lib.inNixShell then drv.env else drv
+  d = haskellPackages.callPackage f {};
+in d // { meta = d.meta // { mainProgram= "marlowe-scan-exe"; }; }