ginsim.nix: Add detailed comments.

ginsim.nix

@@ -6,26 +6,61 @@
 #
 #   nix-build ginsim.nix
 #
-# Or you can use in a nix-shell as shell.nix in the same directory
-# illustrates.
+# This will create the symlink result in the current directory.  The
+# runnable shell script is result/bin/GINsim.
+#
+# You can use this file in a nix-shell, as shell.nix illustrates.
 
 let
+  # Import nixpkgs to be able to supply reasonable default values for
+  # the anonymous function this file defines.
   pkgs = import <nixpkgs> {};
 in
-{ stdenv ? pkgs.stdenv, fetchurl ? pkgs.fetchurl, makeWrapper ? pkgs.makeWrapper, jre ? pkgs.jre }:
+# These arguments define the resources (packages and native Nix tools)
+# that will be used by the package (the anonymous function I define).
+# I want this file to be buildable directly using the command
+# nix-build ginsim.nix, so I have to supply reasonable default values
+# to these arguments.  The default values naturally come from the
+# corresponding attributes of Nixpkgs, visible here under the binding
+# pkgs.
+{ stdenv ? pkgs.stdenv
+, fetchurl ? pkgs.fetchurl
+, makeWrapper ? pkgs.makeWrapper
+, jre ? pkgs.jre
+}:
 
+# I'll use the default builder, because I don't need any particular
+# features.
 stdenv.mkDerivation rec {
   name = "GINsim";
   version = "2.4";
 
+  # Simply fetch the JAR file of GINsim.
   src = fetchurl {
     url = "http://ginsim.org/sites/default/files/${name}-${version}.jar";
     sha256 = "0891q75hli6ghgangscygkqw60x9ikx96i8y4fqca6kdh1xgs15h";
   };
+  # I fetch the JAR file directly, so no archives to unpack.
   dontUnpack = true;
 
+  # I need makeWrapper in my build environment to generate the wrapper
+  # shell script.  This shell script will call the Java executable on
+  # the JAR file of GINsim and will set the appropriate environment
+  # variables.
   nativeBuildInputs = [ makeWrapper ];
 
+  # The only meaningful phase of this build.  I create the
+  # subdirectory share/java/ in the output directory, because this is
+  # where JAR files are typically stored.  I also create the
+  # subdirectory bin/ to store the executable shell script.  I then
+  # copy the downloaded JAR file to $out/share/java/.  Once this is
+  # done, I create the wrapper shell script using makeWrapper.  This
+  # script wraps the Java executable (${jre}/bin/java) in the output
+  # shell script file $out/bin/GINsim.  The script adds the argument
+  # -jar … to the Java executable, thus pointing it to the actual
+  # GINsim JAR file.  On my system (NixOS + XMonad), I need to set
+  # some additional environment variables to get Java windows to
+  # render properly.
   installPhase = ''
   mkdir -pv $out/share/java $out/bin
   cp ${src} $out/share/java/${name}-${version}.jar
@@ -36,10 +71,14 @@ stdenv.mkDerivation rec {
     --set _JAVA_AWT_WM_NONREPARENTING 1
   '';
 
-  meta = {
+  # Some easy metadata, in case I forget.  I use the with statement to
+  # avoid typing stdenv.lib to specify the license, the platform and
+  # the maintainer.
+  meta =  with stdenv.lib; {
     homepage = "http://ginsim.org/";
     description = "A computer tool for the modeling and simulation of genetic regulatory networks.";
-    license = stdenv.lib.licenses.gpl3;
-    platforms = stdenv.lib.platforms.unix;
+    license = licenses.gpl3;
+    platforms = platforms.unix;
+    maintainers = [ maintainers.scolobb ];
   };
 }