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 constant =
      Const_int of int
    | Const_char of char
    | Const_string of string * string option
    | Const_float of string
    | Const_int32 of int32
    | Const_int64 of int64
    | Const_nativeint of nativeint
  type rec_flag = Nonrecursive | Recursive
  type direction_flag = Upto | Downto
  type private_flag = Private | Public
  type mutable_flag = Immutable | Mutable
  type virtual_flag = Virtual | Concrete
  type override_flag = Override | Fresh
  type closed_flag = Closed | Open
  type label = string
  type 'a loc = 'a Location.loc = { txt : 'a; loc : Location.t; }
  type variance = Covariant | Contravariant | Invariant
end