pinning nixpkgs and adding missing dependencies

README.md

@@ -63,3 +63,9 @@ To compare with `reitit` (Clojure framework)
 ```
 
 You can see the visualised results at https://www.techempower.com/benchmarks/#section=test
+
+## Nix
+
+A developer shell.nix file is provided in the `nix` directory
+
+See  [nix/README.md](nix/README.md)

nix/README.md

@@ -21,3 +21,9 @@ a particular ghc version, e.g:
 ``` sh
 $ nix-shell nix/shell.nix --argstr compiler ghcHEAD
 ```
+
+**Possible GHC versions**
+-   `ghc822Binary`
+-   `ghc865`
+-   `ghc884`
+-   `ghc8102` - default

nix/shell.nix

@@ -1,21 +1,25 @@
-{ pkgs ? import <nixpkgs> {}
-, compiler ? "ghc822"
+let nixos = fetchTarball { 
+  url = "https://releases.nixos.org/nixos/20.09/nixos-20.09.3505.12d9950bf47/nixexprs.tar.xz";
+  sha256 = "0fsl8bsdb8i536pfs4wrp0826h5l84xqlwx32sbz66jg4ykqp9lr";
+}; in
+
+{ compiler ? "ghc8102"
 , tutorial ? false
+, pkgs ? import nixos { config = {}; }
 }:
   
-with pkgs;
+  with pkgs;
 
-let
-  ghc = haskell.packages.${compiler}.ghcWithPackages (_: []);
-  docstuffs = python3.withPackages (ps: with ps; [ recommonmark sphinx sphinx_rtd_theme ]);
-in
-
-stdenv.mkDerivation {
-    name = "servant-dev";
-    buildInputs = [ ghc zlib python3 wget ]
-      ++ (if tutorial then [docstuffs postgresql] else []);
-    shellHook = ''
-      eval $(grep export ${ghc}/bin/ghc)
-      export LD_LIBRARY_PATH="${zlib}/lib";
-    '';
-}
+  let
+    ghc = haskell.packages.${compiler}.ghcWithPackages (_: []);
+    docstuffs = python3.withPackages (ps: with ps; [ recommonmark sphinx sphinx_rtd_theme ]);
+  in
+  stdenv.mkDerivation {
+      name = "servant-dev";
+      buildInputs = [ ghc zlib python3 wget cabal-install postgresql openssl ]
+        ++ (if tutorial then [docstuffs postgresql] else []);
+      shellHook = ''
+        eval $(grep export ${ghc}/bin/ghc)
+        export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:"${zlib}/lib";
+      '';
+  }