Move wrapNonNixProgram to utils module

Define the wrapNonNixProgram in my Nix utils module.

configs/.config/nixpkgs/home.nix

@@ -1,9 +1,7 @@
 { config, pkgs, ... }:
 
 let
-  wrapNonNixProgram = { path, as }: pkgs.writeShellScriptBin as ''
-    exec ${path} "$@"
-  '';
+  briefcase = import <briefcase> {};
 in {
   home = {
     packages = with pkgs; [
@@ -45,7 +43,10 @@ in {
 
   programs.git = {
     enable = true;
-    package = wrapNonNixProgram { path = "/usr/bin/git"; as = "git"; };
+    package = briefcase.utils.wrapNonNixProgram {
+      path = "/usr/bin/git";
+      as = "git";
+    };
     userName = "William Carroll";
     userEmail = "wpcarro@gmail.com";
     aliases = {
@@ -147,7 +148,10 @@ in {
     enable = true;
     latitude = "51.49";
     longitude = "-0.18";
-    package = wrapNonNixProgram { path = "/usr/bin/redshift"; as = "redshift"; };
+    package = briefcase.utils.wrapNonNixProgram {
+      path = "/usr/bin/redshift";
+      as = "redshift";
+    };
   };
 
   # Hide the cursor during X sessions after 1 second.

default.nix

@@ -8,6 +8,7 @@ let
   };
 in {
   nixos       = readTree ./nixos;
+  utils       = readTree ./utils;
   emacs       = readTree ./emacs;
   blog        = readTree ./blog;
   lisp        = readTree ./lisp;

utils.nix

@@ -1,5 +0,0 @@
-# Using this as a library to define some common utility functions that I often
-# reach for.
-{
-  identity = x: x;
-}

utils/default.nix

@@ -0,0 +1,14 @@
+{ pkgs, ... }:
+
+# Using this as a library to define some common utility functions that I often
+# reach for.
+{
+  # A unary function that returns its argument.
+  identity = x: x;
+
+  # Create a derivation that creates an executable shell script named `as` that
+  # calls the program located at `path`, forwarding all of the arguments.
+  wrapNonNixProgram = { path, as }: pkgs.writeShellScriptBin as ''
+    exec ${path} "$@"
+  '';
+}