chore: initial commit

lib/compat/default.nix

@@ -0,0 +1,5 @@
+{l}: rec {
+  filter = import ./filter.nix {inherit l;};
+  select = import ./select.nix {inherit filter;};
+  get = import ./get.nix {inherit select;};
+}

lib/compat/filter.nix

@@ -0,0 +1,30 @@
+{l}: let
+  filter = pred: t: p: let
+    multiplePaths = l.isList (l.elemAt p 0);
+    hoist = path: let
+      result =
+        l.filterAttrs (
+          n: v:
+            (l.elem n l.systems.doubles.all)
+            && (l.hasAttrByPath path v)
+        )
+        t;
+    in
+      if result == {}
+      then builtins.abort "[ren] filter: Path ${toString path} not found in any targets."
+      else
+        l.mapAttrs (
+          _: v: let
+            attr = l.getAttrFromPath path v;
+          in
+            if pred == true
+            then attr
+            else l.filterAttrs pred attr
+        )
+        result;
+  in
+    if multiplePaths
+    then l.foldl' l.recursiveUpdate {} (map (path: hoist path) p)
+    else hoist p;
+in
+  filter

lib/compat/get.nix

@@ -0,0 +1,8 @@
+{select}: let
+  get = t: p: let
+    r = select t p;
+    s = builtins.head (builtins.attrNames r);
+  in
+    r.${s};
+in
+  get

lib/compat/select.nix

@@ -0,0 +1,2 @@
+{filter}:
+filter true