Add .cabal file; better, hopefully purer shell.nix

.envrc

@@ -0,0 +1 @@
+use_nix

.gitignore

@@ -1 +1,2 @@
 result*
+dist

all-hies.cabal

@@ -0,0 +1,23 @@
+cabal-version:       2.4
+name:                all-hies
+version:             0.1.0.0
+author:              Silvan Mosberger
+maintainer:          infinisil@icloud.com
+
+executable update
+  main-is:             update.hs
+  build-depends:       base ^>=4.12.0.0
+                     , haskeline
+                     , process
+                     , regex-applicative
+                     , directory
+                     , filepath
+                     , stack2nix
+                     , http-client
+                     , http-client-tls
+                     , time
+                     , aeson
+                     , mtl
+                     , bytestring
+                     , Cabal
+  default-language:    Haskell2010

shell.nix

@@ -1,25 +1,9 @@
 { pkgs ? import ./nixpkgs.nix
 }:
-
-let
-  ghcWithPkgs = pkgs.haskellPackages.ghcWithPackages (p: with p; [
-    directory
-    filepath
-    process
-    http-client
-    http-client-tls
-    aeson
-    regex-applicative
-    haskeline
-    stack2nix
-    cabal-install
-  ]);
-in
-
-pkgs.mkShell {
-  buildInputs = with pkgs; [
-    ghcWithPkgs
-    git
-    nix-prefetch-scripts
+(pkgs.haskellPackages.callCabal2nix "all-hies" ./. {}).env.overrideAttrs (old: {
+  nativeBuildInputs = old.nativeBuildInputs or [] ++ [
+    pkgs.nix-prefetch-scripts
+    pkgs.git
+    pkgs.haskellPackages.cabal-install
   ];
-}
+})

update.hs

@@ -1,5 +1,5 @@
 #!/usr/bin/env nix-shell
-#!nix-shell -i runhaskell shell.nix
+#!nix-shell --pure -i runhaskell shell.nix
 
 {-# LANGUAGE LambdaCase        #-}
 {-# LANGUAGE NamedFieldPuns    #-}