More explicit translation for Function$.

Cosmetic change that will be needed later to remove `Function$`.

Author: cristianoc

compiler/ml/translcore.ml

@@ -823,7 +823,9 @@ and transl_exp0 (e : Typedtree.expression) : Lambda.lambda =
     with Not_constant -> Lprim (Pmakeblock Blk_tuple, ll, e.exp_loc))
   | Texp_construct ({txt = Lident "false"}, _, []) -> Lconst Const_false
   | Texp_construct ({txt = Lident "true"}, _, []) -> Lconst Const_true
-  | Texp_construct ({txt = Lident "Function$"}, _, [expr]) ->
+  | Texp_construct
+      ({txt = Lident "Function$"}, _, [({exp_desc = Texp_function _} as expr)])
+    ->
     (* ReScript uncurried encoding *)
     let loc = expr.exp_loc in
     let lambda = transl_exp expr in