Merge pull request snabbco#32 from lukego/nix-comments

Comment nix expression

README.md

@@ -26,9 +26,9 @@ PRs welcome! Shock me with your radical ideas! :-)
 
 RaptorJIT uses [nix](http://nixos.org/nix/) to define a reproducible
 build environment that includes Clang for C and LuaJIT 2.0 for
-bootstrapping. The recommended way to build RaptorJIT is with nix,
-which provides the dependencies automatically, but you can build
-manually if you prefer.
+bootstrapping (see [default.nix](default.nix)). The recommended way to
+build RaptorJIT is with nix, which provides the dependencies
+automatically, but you can build manually if you prefer.
 
 #### Build with nix
 

default.nix

@@ -1,19 +1,30 @@
-{ pkgs ? (import <nixpkgs> {})
+# default.nix - define the build environment for RaptorJIT
+#
+# This file can be used by 'nix-build' or 'nix-shell' to create a
+# pristine build environment with precisely the expected software in
+# $PATH. This makes it possible to build raptorjit in the same way on
+# any machine.
+#
+# See README.md for usage instructions.
+
+{ pkgs ? (import <nixpkgs> {}) # Use default nix distro (for now...)
 , source ? ./.
 , version ? "dev"
 }:
 
 with pkgs;
-with clangStdenv;
+with clangStdenv;            # Clang instead of GCC
 
 mkDerivation rec {
   name = "raptorjit-${version}";
   inherit version;
   src = lib.cleanSource source;
-  enableParallelBuilding = true;
-  buildInputs = [ luajit ];
+  buildInputs = [ luajit ];  # LuaJIT to bootstrap DynASM
   installPhase = ''
     mkdir -p $out/bin
     cp src/luajit $out/bin/raptorjit
   '';
+
+  enableParallelBuilding = true;  # Do 'make -j'
 }
+