Add helper functions. -> should lead to code deduplication in the future.

fn.nix

@@ -0,0 +1,17 @@
+{ lib }:
+
+with builtins;
+with lib;
+
+rec {
+  ifelse = a: b: c: if a then b else c;
+  cwd = toString ./.;
+  lst = { p ? cwd, t ? "regular", b ? false }: (lists.forEach
+    (attrNames
+      (filterAttrs (n: v: v == t)
+        (readDir p)))
+    (v: ((optionalString b "${p}/")  + v)));
+  lsf = p: (lst { p = p; });
+  lsd = p: (lst { p = p; t = "directory"; b = true; });
+  lsfRec = p: b: flatten ((map (np: lsfRec np b) (lsd p)) ++ (lst { p = p; b = b; }));
+}