diff --git a/coalesce.nix b/coalesce.nix
new file mode 100644
index 0000000..4460422
--- /dev/null
+++ b/coalesce.nix
@@ -0,0 +1,7 @@
+with builtins;
+let fn = y: vs:
+  if vs == [] then null else
+  if head vs != null then head vs else
+  y y (tail vs);
+in
+  fn fn