Merge pull request #990 from ocaml/list-find-exn

Add List.find_exn

bin/main.ml

@@ -181,9 +181,10 @@ let find_root () =
       List.fold_left l ~init:max_int ~f:(fun acc (prio, _, _) ->
         min acc prio)
     in
-    match List.find l ~f:(fun (prio, _, _) -> prio = lowest_priority) with
-    | None -> assert false
-    | Some (_, dir, to_cwd) -> (dir, to_cwd)
+    let (_, dir, to_cwd) =
+      List.find_exn l ~f:(fun (prio, _, _) -> prio = lowest_priority)
+    in
+    (dir, to_cwd)
 
 let package_name =
   Arg.conv ((fun p -> Ok (Package.Name.of_string p)), Package.Name.pp)
@@ -896,11 +897,7 @@ let external_lib_deps =
              in
              if only_missing then begin
                let context =
-                 match
-                   List.find setup.contexts ~f:(fun c -> c.name = context_name)
-                 with
-                 | None -> assert false
-                 | Some c -> c
+                 List.find_exn setup.contexts ~f:(fun c -> c.name = context_name)
                in
                let missing =
                  String.Map.filteri externals ~f:(fun name _ ->

src/build_system.ml

@@ -160,9 +160,9 @@ module Internal_rule = struct
         last_requested_file :: acc
       else
         let requested_file, rev_dep =
-          Option.value_exn
-            (List.find t.rev_deps ~f:(fun (_, t) ->
-               Id.Set.mem t.transitive_rev_deps last.id))
+          List.find_exn
+            t.rev_deps
+            ~f:(fun (_, t) -> Id.Set.mem t.transitive_rev_deps last.id)
         in
         build_loop (requested_file :: acc) rev_dep
     in

src/stdune/list.ml

@@ -77,6 +77,11 @@ let rec find l ~f =
   | [] -> None
   | x :: l -> if f x then Some x else find l ~f
 
+let find_exn l ~f =
+  match find l ~f with
+  | Some x -> x
+  | None -> invalid_arg "List.find_exn"
+
 let rec last = function
   | [] -> None
   | [x] -> Some x

src/stdune/list.mli

@@ -28,6 +28,7 @@ val rev_filter_partition_map
   -> 'b t * 'c t
 
 val find     : 'a t -> f:('a -> bool     ) -> 'a option
+val find_exn : 'a t -> f:('a -> bool     ) -> 'a
 val find_map : 'a t -> f:('a -> 'b option) -> 'b option
 
 val last : 'a t -> 'a option