4 files changed, 58 insertions, 18 deletions
diff --git a/4lib/krebs/default.nix b/4lib/krebs/default.nix
index 0c42a5de3..b67585335 100644
--- a/4lib/krebs/default.nix
+++ b/4lib/krebs/default.nix
@@ -12,22 +12,7 @@ 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.${last path};
-    in
-    if typeOf y != "set"
-      then y
-      else tree-get (init path) y;
-
+  dns = import ./dns.nix { inherit lib; };
+  listset = import ./listset.nix { inherit lib; };
+  tree = import ./tree.nix { inherit lib; };
 }
diff --git a/4lib/krebs/dns.nix b/4lib/krebs/dns.nix
new file mode 100644
index 000000000..b2cf3c24c
--- /dev/null
+++ b/4lib/krebs/dns.nix
@@ -0,0 +1,31 @@
+{ lib, ... }:
+
+let
+  listset = import ./listset.nix { inherit lib; };
+in
+
+with builtins;
+with lib;
+
+rec {
+  # label = string
+
+  # TODO does it make sense to have alias = list label?
+
+  # split-by-provider :
+  #   [[label]] -> tree label provider -> listset provider alias
+  split-by-provider = as: providers:
+    foldl (m: a: listset.insert (provider-of a providers) a m) {} as;
+
+  # provider-of : alias -> tree label provider -> provider
+  # Note that we cannot use tree.get here, because path can be longer
+  # than the tree depth.
+  provider-of = a:
+    let
+      go = path: tree:
+        if typeOf tree == "string"
+          then tree
+          else go (tail path) tree.${head path};
+    in
+    go (reverseList (splitString "." a));
+}
diff --git a/4lib/krebs/listset.nix b/4lib/krebs/listset.nix
new file mode 100644
index 000000000..3aae22f20
--- /dev/null
+++ b/4lib/krebs/listset.nix
@@ -0,0 +1,11 @@
+{ lib, ... }:
+
+with lib;
+
+rec {
+  # listset k v = set k [v]
+
+  # insert : k -> v -> listset k v -> listset k v
+  insert = name: value: set:
+    set // { ${name} = set.${name} or [] ++ [value]; };
+}
diff --git a/4lib/krebs/tree.nix b/4lib/krebs/tree.nix
new file mode 100644
index 000000000..1cd83b3f6
--- /dev/null
+++ b/4lib/krebs/tree.nix
@@ -0,0 +1,13 @@
+{ lib, ... }:
+
+with lib;
+
+rec {
+  # tree k v = set k (either v (tree k v))
+
+  # get : [k] -> tree k v -> v
+  get = path: tree:
+    if length path > 0
+      then get (tail path) tree.${head path} # TODO check if elem exists
+      else tree;
+}