add shell.nix for building servant (+ tutorial + cookbook, optionally)

.gitignore

@@ -25,8 +25,6 @@ cabal.config
 *.hp
 Setup
 .stack-work
-shell.nix
-default.nix
 doc/_build
 doc/venv
 doc/tutorial/static/api.js

nix/README.md

@@ -0,0 +1,23 @@
+You can use the `shell.nix` from this directory
+to build the servant packages or even the tutorial
+or cookbook if you want to, optionally.
+
+Just the servant packages:
+
+``` sh
+$ nix-shell nix/shell.nix
+```
+
+Everything needed for the tutorial and the
+cookbook too:
+
+``` sh
+$ nix-shell nix/shell.nix --arg tutorial true
+```
+
+The `shell.nix` file also supports specifying
+a particular ghc version, e.g:
+
+``` sh
+$ nix-shell nix/shell.nix --argstr compiler ghcHEAD
+```

nix/shell.nix

@@ -0,0 +1,21 @@
+{ pkgs ? import <nixpkgs> {}
+, compiler ? "ghc821"
+, tutorial ? false
+}:
+
+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 ]
+      ++ (if tutorial then [docstuffs postgresql] else []);
+    shellHook = ''
+      eval $(grep export ${ghc}/bin/ghc)
+      export LD_LIBRARY_PATH="${zlib}/lib";
+    '';
+}