allow ignoring additional arguments

dhallToNix.nix

@@ -15,4 +15,4 @@
     nativeBuildInputs = [pkgs.dhall-nix];
   };
 in
-  import "${drv}" (import ./runtime.nix)
+  import "${drv}" (import ./runtime.nix pkgs.lib)

primops.dhall

@@ -5,6 +5,7 @@ let Set = ./Set/Type.dhall
 in  { equal : Any → Any → Bool
     , fix : ∀(t : Type) → (t → t) → t
     , `fix'` : (Set → Set) → Set
+    , ignoreOtherArgs : ∀(A: Type) → ∀(B: Type) → (A → B) → A → B
     , mergeAttrs : Set → Set → Set
     , toAny : ∀(t : Type) → ∀(v : t) → Any
     , toTypeUnchecked : ∀(t : Type) → ∀(v : Any) → t

runtime.nix

@@ -1,8 +1,13 @@
-{
+lib: {
   primops = {
     equal = a: b: a == b;
     fix = _: f: let x = f x; in x;
     fix' = f: let x = f x // { __unfix__ = f; }; in x;
+    ignoreOtherArgs = _: _: f: let
+      args = lib.trivial.functionArgs f;
+      filterFunction = k: _: builtins.hasAttrs k set;
+      filteredFunction = s: f (lib.attrsets.filterAttrs filterFunction s);
+    in lib.trivial.setFunctionArgs filteredFunction args;
     mergeAttrs = a: b: a // b;
     toAny = _: v: v;
     toTypeUnchecked = _: v: v;