Below is the API for the OCaml standard library. It's directly copied over from the OCaml Manual, formatted to the Reason syntax and styled accordingly. The API docs are work-in-progress; we'll be polishing these gradually!
If you're targeting JavaScript, the API docs for BuckleScript includes all of below, plus JS-specific APIs.
sig type ('a, 'b) t = ('a, 'b) Hashtbl.t val create : ?random:bool -> int -> ('a, 'b) MoreLabels.Hashtbl.t val clear : ('a, 'b) MoreLabels.Hashtbl.t -> unit val reset : ('a, 'b) MoreLabels.Hashtbl.t -> unit val copy : ('a, 'b) MoreLabels.Hashtbl.t -> ('a, 'b) MoreLabels.Hashtbl.t val add : ('a, 'b) MoreLabels.Hashtbl.t -> key:'a -> data:'b -> unit val find : ('a, 'b) MoreLabels.Hashtbl.t -> 'a -> 'b val find_all : ('a, 'b) MoreLabels.Hashtbl.t -> 'a -> 'b list val mem : ('a, 'b) MoreLabels.Hashtbl.t -> 'a -> bool val remove : ('a, 'b) MoreLabels.Hashtbl.t -> 'a -> unit val replace : ('a, 'b) MoreLabels.Hashtbl.t -> key:'a -> data:'b -> unit val iter : f:(key:'a -> data:'b -> unit) -> ('a, 'b) MoreLabels.Hashtbl.t -> unit val fold : f:(key:'a -> data:'b -> 'c -> 'c) -> ('a, 'b) MoreLabels.Hashtbl.t -> init:'c -> 'c val length : ('a, 'b) MoreLabels.Hashtbl.t -> int val randomize : unit -> unit type statistics = Hashtbl.statistics val stats : ('a, 'b) MoreLabels.Hashtbl.t -> MoreLabels.Hashtbl.statistics module type HashedType = Hashtbl.HashedType module type SeededHashedType = Hashtbl.SeededHashedType module type S = sig type key and 'a t val create : int -> 'a MoreLabels.Hashtbl.S.t val clear : 'a MoreLabels.Hashtbl.S.t -> unit val reset : 'a MoreLabels.Hashtbl.S.t -> unit val copy : 'a MoreLabels.Hashtbl.S.t -> 'a MoreLabels.Hashtbl.S.t val add : 'a MoreLabels.Hashtbl.S.t -> key:MoreLabels.Hashtbl.S.key -> data:'a -> unit val remove : 'a MoreLabels.Hashtbl.S.t -> MoreLabels.Hashtbl.S.key -> unit val find : 'a MoreLabels.Hashtbl.S.t -> MoreLabels.Hashtbl.S.key -> 'a val find_all : 'a MoreLabels.Hashtbl.S.t -> MoreLabels.Hashtbl.S.key -> 'a list val replace : 'a MoreLabels.Hashtbl.S.t -> key:MoreLabels.Hashtbl.S.key -> data:'a -> unit val mem : 'a MoreLabels.Hashtbl.S.t -> MoreLabels.Hashtbl.S.key -> bool val iter : f:(key:MoreLabels.Hashtbl.S.key -> data:'a -> unit) -> 'a MoreLabels.Hashtbl.S.t -> unit val fold : f:(key:MoreLabels.Hashtbl.S.key -> data:'a -> 'b -> 'b) -> 'a MoreLabels.Hashtbl.S.t -> init:'b -> 'b val length : 'a MoreLabels.Hashtbl.S.t -> int val stats : 'a MoreLabels.Hashtbl.S.t -> MoreLabels.Hashtbl.statistics end module type SeededS = sig type key and 'a t val create : ?random:bool -> int -> 'a MoreLabels.Hashtbl.SeededS.t val clear : 'a MoreLabels.Hashtbl.SeededS.t -> unit val reset : 'a MoreLabels.Hashtbl.SeededS.t -> unit val copy : 'a MoreLabels.Hashtbl.SeededS.t -> 'a MoreLabels.Hashtbl.SeededS.t val add : 'a MoreLabels.Hashtbl.SeededS.t -> key:MoreLabels.Hashtbl.SeededS.key -> data:'a -> unit val remove : 'a MoreLabels.Hashtbl.SeededS.t -> MoreLabels.Hashtbl.SeededS.key -> unit val find : 'a MoreLabels.Hashtbl.SeededS.t -> MoreLabels.Hashtbl.SeededS.key -> 'a val find_all : 'a MoreLabels.Hashtbl.SeededS.t -> MoreLabels.Hashtbl.SeededS.key -> 'a list val replace : 'a MoreLabels.Hashtbl.SeededS.t -> key:MoreLabels.Hashtbl.SeededS.key -> data:'a -> unit val mem : 'a MoreLabels.Hashtbl.SeededS.t -> MoreLabels.Hashtbl.SeededS.key -> bool val iter : f:(key:MoreLabels.Hashtbl.SeededS.key -> data:'a -> unit) -> 'a MoreLabels.Hashtbl.SeededS.t -> unit val fold : f:(key:MoreLabels.Hashtbl.SeededS.key -> data:'a -> 'b -> 'b) -> 'a MoreLabels.Hashtbl.SeededS.t -> init:'b -> 'b val length : 'a MoreLabels.Hashtbl.SeededS.t -> int val stats : 'a MoreLabels.Hashtbl.SeededS.t -> MoreLabels.Hashtbl.statistics end module Make : functor (H : HashedType) -> sig type key = H.t and 'a t val create : int -> 'a t val clear : 'a t -> unit val reset : 'a t -> unit val copy : 'a t -> 'a t val add : 'a t -> key:key -> data:'a -> unit val remove : 'a t -> key -> unit val find : 'a t -> key -> 'a val find_all : 'a t -> key -> 'a list val replace : 'a t -> key:key -> data:'a -> unit val mem : 'a t -> key -> bool val iter : f:(key:key -> data:'a -> unit) -> 'a t -> unit val fold : f:(key:key -> data:'a -> 'b -> 'b) -> 'a t -> init:'b -> 'b val length : 'a t -> int val stats : 'a t -> statistics end module MakeSeeded : functor (H : SeededHashedType) -> sig type key = H.t and 'a t val create : ?random:bool -> int -> 'a t val clear : 'a t -> unit val reset : 'a t -> unit val copy : 'a t -> 'a t val add : 'a t -> key:key -> data:'a -> unit val remove : 'a t -> key -> unit val find : 'a t -> key -> 'a val find_all : 'a t -> key -> 'a list val replace : 'a t -> key:key -> data:'a -> unit val mem : 'a t -> key -> bool val iter : f:(key:key -> data:'a -> unit) -> 'a t -> unit val fold : f:(key:key -> data:'a -> 'b -> 'b) -> 'a t -> init:'b -> 'b val length : 'a t -> int val stats : 'a t -> statistics end val hash : 'a -> int val seeded_hash : int -> 'a -> int val hash_param : int -> int -> 'a -> int val seeded_hash_param : int -> int -> int -> 'a -> int end