2 files changed, 21 insertions, 0 deletions
diff --git a/4lib/krebs/default.nix b/4lib/krebs/default.nix
index 0c59076b6..0c42a5de3 100644
--- a/4lib/krebs/default.nix
+++ b/4lib/krebs/default.nix
@@ -12,4 +12,22 @@ builtins // lib // rec {
 
   types = import ./types.nix { inherit lib; };
 
+
+  # listset k v = set k [v]
+
+  # listset-insert : k -> v -> listset k v -> listset k v
+  listset-insert = name: value: set:
+    set // { ${name} = set.${name} or [] ++ [value]; };
+
+  # tree k v = set k (either v (tree k v))
+
+  # tree-get : [k] -> tree k v -> v
+  tree-get = path: x:
+    let
+      y = x.${last path};
+    in
+    if typeOf y != "set"
+      then y
+      else tree-get (init path) y;
+
 }
diff --git a/4lib/krebs/types.nix b/4lib/krebs/types.nix
index ca92c6900..3d3d75a65 100644
--- a/4lib/krebs/types.nix
+++ b/4lib/krebs/types.nix
@@ -83,6 +83,9 @@ types // rec {
 
   user = submodule {
     options = {
+      mail = mkOption {
+        type = str; # TODO retiolum mail address
+      };
       name = mkOption {
         type = str; # TODO
       };