Add shell.nix to build on NixOS and to build reproducibly

Makefile

@@ -13,6 +13,20 @@ continuous:
 clean:
 	$(LATEXMK) -C book.tex
 
+# Build with a fixed snapshot of NixPkgs 17.03.  Known-to-work.
+# For a very clean version, run git clean -fxd followed by this:
+#
+# This may take a long time and build a complete version of texlive.
+# Since it is fixed-in-time it may not have binary caches available and
+# may need to build from source.
+nix:
+	NIX_PATH=nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/51a83266d164195698f04468d90d2c6238ed3491.tar.gz $(MAKE) nix-head
+
+# Build with whatever version of nixpkgs is in the users environment:
+nix-head:
+	nix-shell --pure --run make
+
+
 # Specific to Fall16:
 publish:
 	scp build/book.pdf tank.soic.indiana.edu:p523-web/book.pdf

shell.nix

@@ -0,0 +1,11 @@
+
+# By default (irreproducibly) use whatever nixpkgs is in path:
+with (import <nixpkgs> {});
+
+# Probably a lower-footprint way of doing this:
+stdenv.mkDerivation {
+  name = "docsEnv";
+  buildInputs = [
+                  texlive.combined.scheme-full
+                ];
+}