make nix-build work

.gitignore

@@ -1,2 +1,3 @@
 elm-stuff
 index.html
+result

default.nix

@@ -0,0 +1,26 @@
+{ sources ? import ./nix/sources.nix { }, nixpkgs ? import sources.nixpkgs { }
+}:
+let gitignore = nixpkgs.callPackage sources.gitignore { };
+in nixpkgs.stdenv.mkDerivation {
+  name = "bad-datalog";
+
+  src = gitignore.gitignoreSource ./.;
+  buildInputs = [ nixpkgs.elmPackages.elm ];
+
+  buildPhase = nixpkgs.elmPackages.fetchElmDeps {
+    elmPackages = import ./nix/elm-srcs.nix;
+    elmVersion = "0.19.1";
+    registryDat = ./nix/registry.dat;
+  };
+
+  # it's a little weird that elm2nix says it's fine to build in the install
+  # phase, but who am I to judge?
+  installPhase = ''
+    mkdir -p $out/share/bad-datalog
+
+    (
+      cd sample-app
+      elm make src/Main.elm --output $out/share/bad-datalog/index.html
+    )
+  '';
+}

nix/sources.json

@@ -1,4 +1,16 @@
 {
+    "gitignore": {
+        "branch": "master",
+        "description": "Nix function for filtering local git sources",
+        "homepage": "",
+        "owner": "hercules-ci",
+        "repo": "gitignore",
+        "rev": "211907489e9f198594c0eb0ca9256a1949c9d412",
+        "sha256": "06j7wpvj54khw0z10fjyi31kpafkr6hi1k0di13k1xp8kywvfyx8",
+        "type": "tarball",
+        "url": "https://github.com/hercules-ci/gitignore/archive/211907489e9f198594c0eb0ca9256a1949c9d412.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
     "niv": {
         "branch": "master",
         "description": "Easy dependency management for Nix projects",