Pin version 0.3 of protolude in nix (#1499)

default.nix

@@ -24,6 +24,7 @@ let
     [
       (import nix/overlays/postgresql-legacy.nix)
       (import nix/overlays/gitignore.nix)
+      (import nix/overlays/haskell-packages)
     ];
 
   pkgs =

nix/overlays/haskell-packages/README.md

@@ -0,0 +1,10 @@
+The `.nix` files in this directory pin specific versions of Haskell packages
+from Hackage. They were generated with `cabal2nix`, e.g.:
+
+```bash
+cabal2nix cabal://protolude > protolude.nix
+
+```
+
+Those overrides might become obsolete as the pinned versions are adopted into
+our pinned version of nixpkgs.

nix/overlays/haskell-packages/default.nix

@@ -0,0 +1,11 @@
+self: super:
+
+{
+  haskellPackages =
+    super.haskellPackages.override {
+      overrides =
+        final: prev: rec {
+          protolude = prev.callPackage ./protolude.nix {};
+        };
+    };
+}

nix/overlays/haskell-packages/protolude.nix

@@ -0,0 +1,18 @@
+{ mkDerivation, array, async, base, bytestring, containers, deepseq
+, ghc-prim, hashable, mtl, mtl-compat, stdenv, stm, text
+, transformers, transformers-compat
+}:
+mkDerivation {
+  pname = "protolude";
+  version = "0.3.0";
+  sha256 = "4083385a9e03fab9201f63ce198b9ced3fbc1c50d6d42574db5e36c757bedcac";
+  isLibrary = true;
+  isExecutable = true;
+  libraryHaskellDepends = [
+    array async base bytestring containers deepseq ghc-prim hashable
+    mtl mtl-compat stm text transformers transformers-compat
+  ];
+  homepage = "https://github.com/sdiehl/protolude";
+  description = "A small prelude";
+  license = stdenv.lib.licenses.mit;
+}