default.nix: Commented

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'
 }
+