diff --git a/default.nix b/default.nix
index 0b12780..54773b8 100644
--- a/default.nix
+++ b/default.nix
@@ -4,7 +4,37 @@ in {
   imports = [ "${sources.home-manager}/nixos" ./modules ];
 
   boot.loader.systemd-boot.enable = true;
-  boot.loader.efi.canTouchEfiVariables = true;
+  # boot.loader.efi.canTouchEfiVariables = true;
+
+  boot.loader = {
+    efi = {
+      canTouchEfiVariables = true;
+      # assuming /boot is the mount point of the  EFI partition in NixOS (as the installation section recommends).
+      efiSysMountPoint = "/boot";
+    };
+    grub = {
+      # despite what the configuration.nix manpage seems to indicate,
+      # as of release 17.09, setting device to "nodev" will still call
+      # `grub-install` if efiSupport is true
+      # (the devices list is not used by the EFI grub install,
+      # but must be set to some value in order to pass an assert in grub.nix)
+      devices = [ "nodev" ];
+      efiSupport = true;
+      enable = true;
+      # set $FS_UUID to the UUID of the EFI partition
+      extraEntries = ''
+        menuentry "Windows" {
+          insmod part_gpt
+          insmod fat
+          insmod search_fs_uuid
+          insmod chain
+          search --fs-uuid --set=root $FS_UUID
+          chainloader /EFI/Microsoft/Boot/bootmgfw.efi
+        }
+      '';
+      version = 2;
+    };
+  };
 
   # Enable the OpenSSH daemon.
   services.openssh.enable = true;
@@ -12,7 +42,10 @@ in {
   # Enable sound.
   sound.enable = true;
 
-  # home-manager.users.adrielus.home.packages = with pkgs; [ bluez bluez-tools ];
+  home-manager.users.adrielus = {
+    manual.manpages.enable = false;
+    # home.packages = with pkgs; [ bluez bluez-tools ];
+  };
 
   # Enable blueman
   # services.blueman.enable = true;
@@ -57,6 +90,8 @@ in {
   #   Service.ExecStart = "${pkgs.bluez}/bin/mpris-proxy";
   #   Install.WantedBy = [ "default.target" ];
   # };
+
   system.stateVersion = "20.03";
+
 }
 
diff --git a/modules/applications/default.nix b/modules/applications/default.nix
index 2f988ae..6f4b4da 100644
--- a/modules/applications/default.nix
+++ b/modules/applications/default.nix
@@ -4,16 +4,17 @@
     ./shells
     # ./wakatime
     ./xmonad
+    ./xmodmap
 
     # ./wine.nix
     ./steam.nix
-    # ./docker.nix
+    ./docker.nix
     ./misc.nix
     ./locale.nix
     # ./memes.nix
     ./alacritty.nix
     ./rofi.nix
-    # ./postgres.nix
+    ./postgres.nix
   ];
 }
 
diff --git a/modules/applications/docker.nix b/modules/applications/docker.nix
index 487eb15..fe9bfa7 100644
--- a/modules/applications/docker.nix
+++ b/modules/applications/docker.nix
@@ -1,7 +1,14 @@
 { pkgs, ... }: {
-  virtualisation.docker.enable = true;
+  virtualisation.docker = {
+    enable = true;
+    liveRestore = false;
+    extraOptions = ''
+      --default-address-pool "base=192.168.100.0/20,size=24"
+    '';
+  };
   home-manager.users.adrielus.home.packages = with pkgs; [
     docker
     docker-compose
+    docker-machine
   ];
 }
diff --git a/modules/applications/git/default.nix b/modules/applications/git/default.nix
index 44c322b..16d59a1 100644
--- a/modules/applications/git/default.nix
+++ b/modules/applications/git/default.nix
@@ -15,6 +15,7 @@
 
       userName = "Matei Adriel";
       userEmail = "rafaeladriel11@gmail.com";
+      extraConfig.core.editor = "nvim";
 
       aliases = import ./aliases.nix;
 
diff --git a/modules/applications/misc.nix b/modules/applications/misc.nix
index 6b67161..cb8a02b 100644
--- a/modules/applications/misc.nix
+++ b/modules/applications/misc.nix
@@ -5,22 +5,29 @@
     exa # ls replacement
     mkpasswd # hash passwords
     gnupg
-    typespeed # speed typing game
-    unixtools.xxd # to dump binary stuff into a text file (used it for a ctf)
+    # typespeed # speed typing game
+    # unixtools.xxd # to dump binary stuff into a text file (used it for a ctf)
     # youtube-dl # download from youtube
     neofetch # display system information
     xclip # copy paste stuff
-    feh # image viewer
+    # feh # image viewer
     unzip # for working with .zip files
     speedtest-cli # test the internet speed and stuff
     # openssl
     # pkgconfig
     # ngrok
-    hugo
+    # hugo
     unrar
     # jdk11o
     # jdk8
     # gtk3
+    gnumake
+    # unison-ucm    
+    xorg.libX11
+    texlive.combined.scheme-full
+    okular
+    zathura
+    cmake
 
     # editors
     # vscodium
@@ -52,7 +59,7 @@
     libreoffice # free office suite
     # edopro # yugioh simulator (my derivation doesn't work yet)
     # akonadi
-    # obs-studio # video recorder
+    obs-studio # video recorder
     # blueman # bluetooth manager
     # freesweep # minesweeper I can play w the keyboard.
     # multimc
diff --git a/modules/applications/xmodmap/.Xmodmap b/modules/applications/xmodmap/.Xmodmap
new file mode 100644
index 0000000..0ab19eb
--- /dev/null
+++ b/modules/applications/xmodmap/.Xmodmap
@@ -0,0 +1,5 @@
+! Remap caps lock to control
+clear lock
+clear control
+add control = Caps_Lock Control_L Control_R
+keycode 66 = Control_L Caps_Lock NoSymbol NoSymbol
\ No newline at end of file
diff --git a/modules/applications/xmodmap/default.nix b/modules/applications/xmodmap/default.nix
new file mode 100644
index 0000000..9f9a7b0
--- /dev/null
+++ b/modules/applications/xmodmap/default.nix
@@ -0,0 +1,8 @@
+{ pkgs, ... }: {
+  home-manager.users.adrielus.home = {
+    packages = [ pkgs.xorg.xmodmap ];
+    file.".Xmodmap".source = ./.Xmodmap;
+  };
+  services.xserver.displayManager.sessionCommands =
+    "${pkgs.xorg.xmodmap}/bin/xmodmap .Xmodmap";
+}
diff --git a/modules/dev/default.nix b/modules/dev/default.nix
index ccb7afe..f1d102e 100644
--- a/modules/dev/default.nix
+++ b/modules/dev/default.nix
@@ -6,8 +6,9 @@
     ./javascript.nix
     ./fsharp.nix
     ./rust.nix
-    ./racket.nix
-    ./elm.nix
+    ./idris.nix
+    # ./racket.nix
+    # ./elm.nix
     ./dhall.nix
     ./haskell
   ];
diff --git a/modules/dev/fsharp.nix b/modules/dev/fsharp.nix
index 58aa114..7f47d43 100644
--- a/modules/dev/fsharp.nix
+++ b/modules/dev/fsharp.nix
@@ -1,3 +1,7 @@
 { pkgs, ... }: {
-  home-manager.users.adrielus.home.packages = with pkgs; [ dotnet-sdk mono ];
+  home-manager.users.adrielus.home.packages = with pkgs; [
+    dotnet-sdk
+    mono
+    packet
+  ];
 }
diff --git a/modules/dev/haskell/default.nix b/modules/dev/haskell/default.nix
index a795e24..b3d60e3 100644
--- a/modules/dev/haskell/default.nix
+++ b/modules/dev/haskell/default.nix
@@ -1,11 +1,11 @@
 { pkgs, ... }:
-let hie = pkgs.all-hies.selection { selector = p: { inherit (p) ghc865; }; };
-in {
+# let hie = pkgs.all-hies.selection { selector = p: { inherit (p) ghc865; }; };
+{
   home-manager.users.adrielus.home = {
     file.".ghci".source = ./ghci;
 
     packages = with pkgs;
       [ ghc ghcid hlint cabal-install snack stack ]
-      ++ (with haskellPackages; [ brittany hoogle hpack pointfree ]);
+      ++ (with haskellPackages; [ brittany hoogle hpack ]);
   };
 }
diff --git a/modules/dev/haskell/ghci b/modules/dev/haskell/ghci
index 5dfbb66..4ea943a 100644
--- a/modules/dev/haskell/ghci
+++ b/modules/dev/haskell/ghci
@@ -5,6 +5,6 @@
 :def hoogle-all \str -> return $ ":! hoogle search --color "            ++ show str
 :def doc        \str -> return $ ":! hoogle search --color --info "     ++ show str
 
-:def pointfree \str -> return $ ":! pointfree " ++ show str
-:def pf        \str -> return $ ":! pointfree " ++ show str
+-- :def pointfree \str -> return $ ":! pointfree " ++ show str
+-- :def pf        \str -> return $ ":! pointfree " ++ show str
 -- :def pointful  \str -> return $ ":! pointful " ++ show str
\ No newline at end of file
diff --git a/modules/dev/idris.nix b/modules/dev/idris.nix
new file mode 100644
index 0000000..47798cd
--- /dev/null
+++ b/modules/dev/idris.nix
@@ -0,0 +1,3 @@
+{ pkgs, ... }: {
+  home-manager.users.adrielus.home.packages = with pkgs; [ idris2 ];
+}
diff --git a/modules/dev/javascript.nix b/modules/dev/javascript.nix
index 304d927..dd29a6d 100644
--- a/modules/dev/javascript.nix
+++ b/modules/dev/javascript.nix
@@ -14,11 +14,12 @@ in {
       pnpm
       yarn
 
-      tsdx
-      mklicense
-      preact-cli
-      create-next-app
-      create-snowpack-app
-      bower
+      /* tsdx
+            mklicense
+            preact-cli
+            create-next-app
+            create-snowpack-app
+            bower
+      */
     ];
 }
diff --git a/modules/overlay.nix b/modules/overlay.nix
index ca54717..9f8a50b 100644
--- a/modules/overlay.nix
+++ b/modules/overlay.nix
@@ -27,12 +27,15 @@ in {
 
         # unstable stuff
         brave = unstable.brave;
+        idris2 = unstable.idris2;
         ngrok = unstable.ngrok;
         vscodium = unstable.vscodium;
+        vscode = unstable.vscode;
         docker-compose = unstable.docker-compose;
         deno = unstable.deno;
+        # discord = unstable.discord;
         discord-canary = unstable.discord-canary;
-        dotnet-sdk = dotnet-sdk_3;
+        dotnet-sdk = unstable.dotnet-sdk_5;
         elm-repl = unstable.haskellPackages.elm-repl;
       })
   ];
diff --git a/nix/sources.json b/nix/sources.json
index 1a9bed5..7e07a50 100644
--- a/nix/sources.json
+++ b/nix/sources.json
@@ -5,10 +5,10 @@
         "homepage": "",
         "owner": "nix-community",
         "repo": "NUR",
-        "rev": "05a29a61a994685404ce141957c99ac65628ec25",
-        "sha256": "143nh2ag1dj67vg66wdmkscxa7xfic7balxg0hvymvhzzp18rbw2",
+        "rev": "cfe9e2e5ae53250337b0ffb3f39b477ca09cd232",
+        "sha256": "1zr8mcxp6gpiv7hy7g94giry0gfak8rbvmsi4f8vrry0jvvhp8x7",
         "type": "tarball",
-        "url": "https://github.com/nix-community/NUR/archive/05a29a61a994685404ce141957c99ac65628ec25.tar.gz",
+        "url": "https://github.com/nix-community/NUR/archive/cfe9e2e5ae53250337b0ffb3f39b477ca09cd232.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "agnoster": {
@@ -17,10 +17,10 @@
         "homepage": null,
         "owner": "oh-my-fish",
         "repo": "theme-agnoster",
-        "rev": "99d4e9f1b6bb1c828155495bddf3e0f0516e35f1",
-        "sha256": "0vyg30zi3xhl7m2y40ihb7ikwifz5ifq5wq0y58rz9hpb19wf8ws",
+        "rev": "43860ce1536930bca689470e26083b0a5b7bd6ae",
+        "sha256": "16k94hz3s6wayass6g1lhlcjmbpf2w8mzx90qrrqp120h80xwp25",
         "type": "tarball",
-        "url": "https://github.com/oh-my-fish/theme-agnoster/archive/99d4e9f1b6bb1c828155495bddf3e0f0516e35f1.tar.gz",
+        "url": "https://github.com/oh-my-fish/theme-agnoster/archive/43860ce1536930bca689470e26083b0a5b7bd6ae.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "all-hies": {
@@ -29,10 +29,10 @@
         "homepage": "",
         "owner": "Infinisil",
         "repo": "all-hies",
-        "rev": "09ba836904fa290b5e37d5403150ea0c921661fb",
-        "sha256": "0qbjqv1fkhkx1cffqybz1mfks1jphh0vh3zd8ad2qd6lch4gyys4",
+        "rev": "2364c7bdf5eec60a4765486d16f9ae6be5cd8a78",
+        "sha256": "083k1xxjpdgfkbvadbw6sdbll52807iwzs1fsy1b5axjijsc5qgh",
         "type": "tarball",
-        "url": "https://github.com/Infinisil/all-hies/archive/09ba836904fa290b5e37d5403150ea0c921661fb.tar.gz",
+        "url": "https://github.com/Infinisil/all-hies/archive/2364c7bdf5eec60a4765486d16f9ae6be5cd8a78.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "cached-nix-shell": {
@@ -41,10 +41,10 @@
         "homepage": "",
         "owner": "xzfc",
         "repo": "cached-nix-shell",
-        "rev": "48dbef37bec653e23c1801cea3979f053e10654b",
-        "sha256": "0w6khry1ncyqy5h6996xw1f6viw4wdrfji5m8lz9gm487xlq5v0b",
+        "rev": "8b87dc0047f35fec4f7a132d0e1b67d0526a22f5",
+        "sha256": "1cryshs5w67xg8j3dsy3z4ia6hxzdv6jzz25jwd1m27jci4035qy",
         "type": "tarball",
-        "url": "https://github.com/xzfc/cached-nix-shell/archive/48dbef37bec653e23c1801cea3979f053e10654b.tar.gz",
+        "url": "https://github.com/xzfc/cached-nix-shell/archive/8b87dc0047f35fec4f7a132d0e1b67d0526a22f5.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "easy-dhall-nix": {
@@ -53,10 +53,10 @@
         "homepage": "",
         "owner": "justinwoo",
         "repo": "easy-dhall-nix",
-        "rev": "3e9101c5dfd69a9fc28fe4998aff378f91bfcb64",
-        "sha256": "1nsn1n4sx4za6jipcid1293rdw8lqgj9097s0khiij3fz0bzhrg9",
+        "rev": "1f6eecab5c276a59858a10bbfcbbc5611187da03",
+        "sha256": "07n7y93xfiwr82yx2v8r5mxcafsxgs1hdl1ghq6xah5v827fb6q0",
         "type": "tarball",
-        "url": "https://github.com/justinwoo/easy-dhall-nix/archive/3e9101c5dfd69a9fc28fe4998aff378f91bfcb64.tar.gz",
+        "url": "https://github.com/justinwoo/easy-dhall-nix/archive/1f6eecab5c276a59858a10bbfcbbc5611187da03.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "easy-purescript-nix": {
@@ -65,10 +65,10 @@
         "homepage": "",
         "owner": "justinwoo",
         "repo": "easy-purescript-nix",
-        "rev": "7ff5a12af5750f94d0480059dba0ba6b82c6c452",
-        "sha256": "0af25dqhs13ii4mx9jjkx2pww4ddbs741vb5gfc5ckxb084d69fq",
+        "rev": "47bdc016c7d56e987ca1aca690b1d6c9816a8584",
+        "sha256": "051fzxd03y0c63sll2bhn0h66dywy9lw6ylyh5vq8fymvix20q94",
         "type": "tarball",
-        "url": "https://github.com/justinwoo/easy-purescript-nix/archive/7ff5a12af5750f94d0480059dba0ba6b82c6c452.tar.gz",
+        "url": "https://github.com/justinwoo/easy-purescript-nix/archive/47bdc016c7d56e987ca1aca690b1d6c9816a8584.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "home-manager": {
@@ -77,10 +77,10 @@
         "homepage": "https://rycee.gitlab.io/home-manager/",
         "owner": "rycee",
         "repo": "home-manager",
-        "rev": "318bc0754ed6370cfcae13183a7f13f7aa4bc73f",
-        "sha256": "0hgn85yl7gixw1adjfa9nx8axmlpw5y1883lzg3zigknx6ff5hsr",
+        "rev": "e6f96b6aa3e99495f9f6f3488ecf78dd316e5bec",
+        "sha256": "1xvxqw5cldlhcl7xsbw11n2s3x1h2vmbm1b9b69a641rzj3srg11",
         "type": "tarball",
-        "url": "https://github.com/rycee/home-manager/archive/318bc0754ed6370cfcae13183a7f13f7aa4bc73f.tar.gz",
+        "url": "https://github.com/rycee/home-manager/archive/e6f96b6aa3e99495f9f6f3488ecf78dd316e5bec.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "niv": {
@@ -89,10 +89,10 @@
         "homepage": "https://github.com/nmattia/niv",
         "owner": "nmattia",
         "repo": "niv",
-        "rev": "303f442c43f918bc43400ab4a0b662a82ca7748b",
-        "sha256": "19z1qypd6zd4qzhrhjm7j55v85fzf8wln8l9vslvn9dpspcwxv7c",
+        "rev": "e0ca65c81a2d7a4d82a189f1e23a48d59ad42070",
+        "sha256": "1pq9nh1d8nn3xvbdny8fafzw87mj7gsmp6pxkdl65w2g18rmcmzx",
         "type": "tarball",
-        "url": "https://github.com/nmattia/niv/archive/303f442c43f918bc43400ab4a0b662a82ca7748b.tar.gz",
+        "url": "https://github.com/nmattia/niv/archive/e0ca65c81a2d7a4d82a189f1e23a48d59ad42070.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "nixpkgs": {
@@ -101,22 +101,22 @@
         "homepage": "https://github.com/NixOS/nixpkgs",
         "owner": "NixOS",
         "repo": "nixpkgs-channels",
-        "rev": "0c0fe6d85b92c4e992e314bd6f9943413af9a309",
-        "sha256": "03q0dzxpd55xmvxzr963hv3nxh57m5d7sgiw5kvhpms1hf8lwd4r",
+        "rev": "6d1a044fc9ff3cc96fca5fa3ba9c158522bbf2a5",
+        "sha256": "07a3nyrj3pwl017ig0rbn5rbmbf14gl3vqggvkyrdby01726p5fg",
         "type": "tarball",
-        "url": "https://github.com/NixOS/nixpkgs-channels/archive/0c0fe6d85b92c4e992e314bd6f9943413af9a309.tar.gz",
+        "url": "https://github.com/NixOS/nixpkgs-channels/archive/6d1a044fc9ff3cc96fca5fa3ba9c158522bbf2a5.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "nixpkgs-unstable": {
         "branch": "nixos-unstable",
-        "description": "A read-only mirror of NixOS/nixpkgs tracking the released channels. Send issues and PRs to",
-        "homepage": "https://github.com/NixOS/nixpkgs",
-        "owner": "nixos",
-        "repo": "nixpkgs-channels",
-        "rev": "8e2b14aceb1d40c7e8b84c03a7c78955359872bb",
-        "sha256": "0zzjpd9smr7rxzrdf6raw9kbj42fbvafxb5bz36lcxgv290pgsm8",
+        "description": "Nix Packages collection",
+        "homepage": "",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "7e567a3d092b7de69cdf5deaeb8d9526de230916",
+        "sha256": "0gnbxg435pnp727gbakifqkjnf2pm7qsq2b6767rj4si4w60v96v",
         "type": "tarball",
-        "url": "https://github.com/nixos/nixpkgs-channels/archive/8e2b14aceb1d40c7e8b84c03a7c78955359872bb.tar.gz",
+        "url": "https://github.com/NixOS/nixpkgs/archive/7e567a3d092b7de69cdf5deaeb8d9526de230916.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "snack": {
@@ -125,10 +125,10 @@
         "homepage": "",
         "owner": "nmattia",
         "repo": "snack",
-        "rev": "b638463b9a7490867b44d0c33bb02e8f7ca82f29",
-        "sha256": "02h4f0nrjvhsm7hvmrnc4kfi5my48d7yvind0f1kq1lsrcch6iph",
+        "rev": "2c490a259a7670192744021fb87bf7e430a4e7f0",
+        "sha256": "1v9b9bimw2nx0f2v94hjxlmsb7s82idrpc9dvjabqm92f9yc3kx9",
         "type": "tarball",
-        "url": "https://github.com/nmattia/snack/archive/b638463b9a7490867b44d0c33bb02e8f7ca82f29.tar.gz",
+        "url": "https://github.com/nmattia/snack/archive/2c490a259a7670192744021fb87bf7e430a4e7f0.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     }
 }
diff --git a/nix/sources.nix b/nix/sources.nix
index 7bd0f3e..1938409 100644
--- a/nix/sources.nix
+++ b/nix/sources.nix
@@ -6,25 +6,33 @@ let
   # The fetchers. fetch_<type> fetches specs of type <type>.
   #
 
-  fetch_file = pkgs: spec:
-    if spec.builtin or true then
-      builtins_fetchurl { inherit (spec) url sha256; }
-    else
-      pkgs.fetchurl { inherit (spec) url sha256; };
+  fetch_file = pkgs: name: spec:
+    let
+      name' = sanitizeName name + "-src";
+    in
+      if spec.builtin or true then
+        builtins_fetchurl { inherit (spec) url sha256; name = name'; }
+      else
+        pkgs.fetchurl { inherit (spec) url sha256; name = name'; };
 
   fetch_tarball = pkgs: name: spec:
     let
-      ok = str: ! builtins.isNull (builtins.match "[a-zA-Z0-9+-._?=]" str);
-      # sanitize the name, though nix will still fail if name starts with period
-      name' = stringAsChars (x: if ! ok x then "-" else x) "${name}-src";
+      name' = sanitizeName name + "-src";
     in
       if spec.builtin or true then
         builtins_fetchTarball { name = name'; inherit (spec) url sha256; }
       else
         pkgs.fetchzip { name = name'; inherit (spec) url sha256; };
 
-  fetch_git = spec:
-    builtins.fetchGit { url = spec.repo; inherit (spec) rev ref; };
+  fetch_git = name: spec:
+    let
+      ref =
+        if spec ? ref then spec.ref else
+          if spec ? branch then "refs/heads/${spec.branch}" else
+            if spec ? tag then "refs/tags/${spec.tag}" else
+              abort "In git source '${name}': Please specify `ref`, `tag` or `branch`!";
+    in
+      builtins.fetchGit { url = spec.repo; inherit (spec) rev; inherit ref; };
 
   fetch_local = spec: spec.path;
 
@@ -40,11 +48,21 @@ let
   # Various helpers
   #
 
+  # https://github.com/NixOS/nixpkgs/pull/83241/files#diff-c6f540a4f3bfa4b0e8b6bafd4cd54e8bR695
+  sanitizeName = name:
+    (
+      concatMapStrings (s: if builtins.isList s then "-" else s)
+        (
+          builtins.split "[^[:alnum:]+._?=-]+"
+            ((x: builtins.elemAt (builtins.match "\\.*(.*)" x) 0) name)
+        )
+    );
+
   # The set of packages used when specs are fetched using non-builtins.
-  mkPkgs = sources:
+  mkPkgs = sources: system:
     let
       sourcesNixpkgs =
-        import (builtins_fetchTarball { inherit (sources.nixpkgs) url sha256; }) {};
+        import (builtins_fetchTarball { inherit (sources.nixpkgs) url sha256; }) { inherit system; };
       hasNixpkgsPath = builtins.any (x: x.prefix == "nixpkgs") builtins.nixPath;
       hasThisAsNixpkgsPath = <nixpkgs> == ./.;
     in
@@ -64,15 +82,27 @@ let
 
     if ! builtins.hasAttr "type" spec then
       abort "ERROR: niv spec ${name} does not have a 'type' attribute"
-    else if spec.type == "file" then fetch_file pkgs spec
+    else if spec.type == "file" then fetch_file pkgs name spec
     else if spec.type == "tarball" then fetch_tarball pkgs name spec
-    else if spec.type == "git" then fetch_git spec
+    else if spec.type == "git" then fetch_git name spec
     else if spec.type == "local" then fetch_local spec
     else if spec.type == "builtin-tarball" then fetch_builtin-tarball name
     else if spec.type == "builtin-url" then fetch_builtin-url name
     else
       abort "ERROR: niv spec ${name} has unknown type ${builtins.toJSON spec.type}";
 
+  # If the environment variable NIV_OVERRIDE_${name} is set, then use
+  # the path directly as opposed to the fetched source.
+  replace = name: drv:
+    let
+      saneName = stringAsChars (c: if isNull (builtins.match "[a-zA-Z0-9]" c) then "_" else c) name;
+      ersatz = builtins.getEnv "NIV_OVERRIDE_${saneName}";
+    in
+      if ersatz == "" then drv else
+        # this turns the string into an actual Nix path (for both absolute and
+        # relative paths)
+        if builtins.substring 0 1 ersatz == "/" then /. + ersatz else /. + builtins.getEnv "PWD" + "/${ersatz}";
+
   # Ports of functions for older nix versions
 
   # a Nix version of mapAttrs if the built-in doesn't exist
@@ -89,25 +119,29 @@ let
 
   # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/strings.nix#L269
   stringAsChars = f: s: concatStrings (map f (stringToCharacters s));
+  concatMapStrings = f: list: concatStrings (map f list);
   concatStrings = builtins.concatStringsSep "";
 
+  # https://github.com/NixOS/nixpkgs/blob/8a9f58a375c401b96da862d969f66429def1d118/lib/attrsets.nix#L331
+  optionalAttrs = cond: as: if cond then as else {};
+
   # fetchTarball version that is compatible between all the versions of Nix
-  builtins_fetchTarball = { url, name, sha256 }@attrs:
+  builtins_fetchTarball = { url, name ? null, sha256 }@attrs:
     let
       inherit (builtins) lessThan nixVersion fetchTarball;
     in
       if lessThan nixVersion "1.12" then
-        fetchTarball { inherit name url; }
+        fetchTarball ({ inherit url; } // (optionalAttrs (!isNull name) { inherit name; }))
       else
         fetchTarball attrs;
 
   # fetchurl version that is compatible between all the versions of Nix
-  builtins_fetchurl = { url, sha256 }@attrs:
+  builtins_fetchurl = { url, name ? null, sha256 }@attrs:
     let
       inherit (builtins) lessThan nixVersion fetchurl;
     in
       if lessThan nixVersion "1.12" then
-        fetchurl { inherit url; }
+        fetchurl ({ inherit url; } // (optionalAttrs (!isNull name) { inherit name; }))
       else
         fetchurl attrs;
 
@@ -119,14 +153,15 @@ let
         then abort
           "The values in sources.json should not have an 'outPath' attribute"
         else
-          spec // { outPath = fetch config.pkgs name spec; }
+          spec // { outPath = replace name (fetch config.pkgs name spec); }
     ) config.sources;
 
   # The "config" used by the fetchers
   mkConfig =
-    { sourcesFile ? ./sources.json
-    , sources ? builtins.fromJSON (builtins.readFile sourcesFile)
-    , pkgs ? mkPkgs sources
+    { sourcesFile ? if builtins.pathExists ./sources.json then ./sources.json else null
+    , sources ? if isNull sourcesFile then {} else builtins.fromJSON (builtins.readFile sourcesFile)
+    , system ? builtins.currentSystem
+    , pkgs ? mkPkgs sources system
     }: rec {
       # The sources, i.e. the attribute set of spec name to spec
       inherit sources;
@@ -134,5 +169,6 @@ let
       # The "pkgs" (evaluated nixpkgs) to use for e.g. non-builtin fetchers
       inherit pkgs;
     };
+
 in
 mkSources (mkConfig {}) // { __functor = _: settings: mkSources (mkConfig settings); }