[sledge] Avoid matching on Not_found

Summary: base 0.13 breaks it (sometimes).

Reviewed By: jvillard

Differential Revision: D18717807

fbshipit-source-id: e27a4d6da

sledge/src/llair/term.ml

@@ -395,7 +395,7 @@ module Var = struct
       Map.fold sub ~init:Set.empty ~f:(fun ~key:_ ~data range ->
           Set.add range data )
 
-    let apply sub v = try Map.find_exn sub v with Caml.Not_found -> v
+    let apply sub v = Map.find sub v |> Option.value ~default:v
 
     let apply_set sub vs =
       Map.fold sub ~init:vs ~f:(fun ~key ~data vs ->

sledge/src/symbheap/equality.ml

@@ -107,7 +107,7 @@ let invariant r =
 let true_ = {sat= true; rep= empty_map} |> check invariant
 
 (** apply a subst to a term *)
-let apply s a = try Map.find_exn s a with Caml.Not_found -> a
+let apply s a = Map.find s a |> Option.value ~default:a
 
 (** apply a subst to maximal non-interpreted subterms *)
 let rec norm s a =