From the paper by Jean-Christophe Filliâtre, "A persistent Union-Find data structure", see the ps version
val make : int -> 'a -> 'a tmake n x returns a persistent array of length n, with x. All the elements of this new array are initially physically equal to x (in the sense of the == predicate). Consequently, if x is mutable, it is shared among all elements of the array, and modifying x through one of the array entries will modify all other entries at the same time.
Invalid_argument if n < 0 or n > Sys.max_array_length. If the value of x is a floating-point number, then the maximum size is only Sys.max_array_length / 2.
val init : int -> (int -> 'a) -> 'a tmake n f returns a persistent array of length n, with element i initialized to the result of f i.
Invalid_argument if n < 0 or n > Sys.max_array_length. If the value of x is a floating-point number, then the maximum size is only Sys.max_array_length / 2.
val get : 'a t -> int -> 'aget a i returns the element with index i from the array a.
Invalid_argument "index out of bounds" if n is outside the range 0 to Array.length a - 1.
set a i v sets the element index i from the array a to v.
Invalid_argument "index out of bounds" if n is outside the range 0 to Array.length a - 1.
val length : 'a t -> intReturns the length of the persistent array.
Applies the given function to all elements of the array, and returns a persistent array initialized by the results of f. In the case of mapi, the function is also given the index of the element. It is equivalent to fun f t -> init (fun i -> f (get t i)).
val iter : ('a -> unit) -> 'a t -> unitval iteri : (int -> 'a -> unit) -> 'a t -> unititer f t applies function f to all elements of the persistent array, in order from element 0 to element length t - 1.
val fold_left : ('a -> 'b -> 'a) -> 'a -> 'b t -> 'aval fold_right : ('a -> 'b -> 'b) -> 'a t -> 'b -> 'bFold on the elements of the array.
val to_array : 'a t -> 'a arrayto_array t returns a mutable copy of t.
val of_array : 'a array -> 'a tfrom_array a returns an immutable copy of a.
val to_list : 'a t -> 'a listto_list t returns the list of elements in t.
val of_list : 'a list -> 'a tof_list l returns a fresh persistent array containing the elements of l.
val of_rev_list : 'a list -> 'a tof_rev_list l is the same as of_list (List.rev l) but more efficient
type 'a printer = Format.formatter -> 'a -> unit