val ( ++ ) : ('a -> 'b) -> ('c -> 'a) -> 'c -> 'b
val findi : ('a -> bool) -> 'a list -> (int * 'a)
val option_map : ('a -> 'b) -> 'a option -> 'b option
+val option_get : ('a option) -> 'a
val find_opt : ('a -> 'b option) -> 'a list -> 'b option
val index_of : ?eq:('a -> 'a -> bool) -> 'a -> 'a list -> int
val index_of_opt : ?eq:('a -> 'a -> bool) -> 'a list -> 'a -> int option