1 files changed, 17 insertions, 0 deletions
diff --git a/krebs/4lib/default.nix b/krebs/4lib/default.nix
index bfe8c581c..afff17296 100644
--- a/krebs/4lib/default.nix
+++ b/krebs/4lib/default.nix
@@ -15,6 +15,16 @@ let out = rec {
 
   addNames = mapAttrs addName;
 
+  guard = spec@{ type, value, ... }:
+    assert isOptionType type;
+    if type.check value
+      then value
+      else throw (toString (filter isString [
+        "argument"
+        (if spec ? name then "‘${spec.name}’" else null)
+        "is not a ${type.name}"
+      ]));
+
   types = import ./types.nix {
     inherit config;
     lib = lib // { inherit genid optionalTrace; };
@@ -27,6 +37,11 @@ let out = rec {
   shell = import ./shell.nix { inherit lib; };
   tree = import ./tree.nix { inherit lib; };
 
+  lpad = n: c: s:
+    if stringLength s < n
+      then lpad n c (c + s)
+      else s;
+
   toC = x: let
     type = typeOf x;
     reject = throw "cannot convert ${type}";
@@ -41,6 +56,8 @@ let out = rec {
     mapAttrs (name: _: path + "/${name}")
              (filterAttrs (_: eq "directory") (readDir path));
 
+  genAttrs' = names: f: listToAttrs (map f names);
+
   setAttr = name: value: set: set // { ${name} = value; };
 
   optionalTrace = c: msg: x: if c then trace msg x else x;