pkgs: Add bang-evaluator

I don’t know if (and doubt that) this is a good solution. I can’t simply
callPackage it, since it does not use a callPackage compatible nix
expression but rather a ready-to-build default.nix. Also, I need the
source in two different files, one of which can’t use nixpkgs fetchers.

pkgs/default.nix

@@ -1,4 +1,10 @@
-self: super: {
+self: super:
+let
+  srcs = import ./srcs.nix;
+in
+{
+  bang-evaluator = import srcs.bang-evaluator { pkgs = self; };
+
   bwrap-helper = super.callPackage ./bwrap-helper { };
 
   osu-lazer = super.callPackage ./osu-lazer { inherit (super) osu-lazer; };

pkgs/modules.nix

@@ -1,5 +1,10 @@
+{ pkgs, ... }:
+let
+  srcs = import ./srcs.nix;
+in
 {
   imports = [
     ./wordclock-dimmer/module.nix
+    "${srcs.bang-evaluator}/module.nix"
   ];
 }

pkgs/srcs.nix

@@ -0,0 +1,6 @@
+{
+  bang-evaluator = builtins.fetchTarball {
+    url = "https://git.sbruder.de/simon/bangs/archive/ca0d9ed47b21d7424a3b8be7bb55c55c62d17d3a.tar.gz";
+    sha256 = "1dk5lrhfnyqq604ih584kdb9z3zg49rp9y6b0ai3g5i3f0lwcfw7";
+  };
+}