package containers

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package containers
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Random Generators

type state = Random.State.t
type 'a t = state -> 'a

Random generator for values of type 'a

type 'a random_gen = 'a t
val return : 'a -> 'a t

return x is the generator that always returns x. Example: let random_int = return 4 (* fair dice roll *)

val flat_map : ('a -> 'b t) -> 'a t -> 'b t
val (>>=) : 'a t -> ('a -> 'b t) -> 'b t
val map : ('a -> 'b) -> 'a t -> 'b t
val (>|=) : 'a t -> ('a -> 'b) -> 'b t
val delay : (unit -> 'a t) -> 'a t

Delay evaluation. Useful for side-effectful generators that need some code to run for every call. Example:

let gensym = let r = ref 0 in fun () -> incr r; !r ;;

delay (fun () ->
  let name = gensym() in
  small_int >>= fun i -> return (name,i)
)
  • since 0.4
val choose : 'a t list -> 'a option t

Choose a generator within the list.

val choose_exn : 'a t list -> 'a t

Same as choose but without option.

  • raises Invalid_argument

    if the list is empty

val choose_array : 'a t array -> 'a option t
val choose_return : 'a list -> 'a t

Choose among the list

  • raises Invalid_argument

    if the list is empty

val replicate : int -> 'a t -> 'a list t

replace n g makes a list of n elements which are all generated randomly using g

val list_seq : 'a t list -> 'a list t

Build random lists from lists of random generators

  • since 0.4
val small_int : int t
val int : int -> int t
val int_range : int -> int -> int t

Inclusive range

val small_float : float t

A reasonably small float.

  • since 0.6.1
val float : float -> float t

Random float within the given range

  • since 0.6.1
val float_range : float -> float -> float t

Inclusive range

  • since 0.6.1
val split : int -> (int * int) option t

Split a positive value n into n1,n2 where n = n1 + n2.

  • returns

    None if the value is too small

val split_list : int -> len:int -> int list option t

Split a value n into a list of values whose sum is n and whose length is length.

  • returns

    None if the value is too small

val retry : ?max:int -> 'a option t -> 'a option t

retry g calls g until it returns some value, or until the maximum number of retries was reached. If g fails, then it counts for one iteration, and the generator retries.

  • parameter max:

    maximum number of retries. Default 10

val try_successively : 'a option t list -> 'a option t

try_successively l tries each generator of l, one after the other. If some generator succeeds its result is returned, else the next generator is tried

val (<?>) : 'a option t -> 'a option t -> 'a option t

a <?> b is a choice operator. It first tries a, and returns its result if successful. If a fails, then b is returned.

val fix : ?sub1:('a t -> 'a t) list -> ?sub2:('a t -> 'a t -> 'a t) list -> ?subn:(int t * ('a list t -> 'a t)) list -> base:'a t -> int t -> 'a t

Recursion combinators, for building recursive values. The integer generator is used to provide fuel. The sub_ generators should use their arguments only once!

  • parameter sub1

    cases that recurse on one value

  • parameter sub2

    cases that use the recursive gen twice

  • parameter subn

    cases that use a list of recursive cases

Applicative
val pure : 'a -> 'a t
val (<*>) : ('a -> 'b) t -> 'a t -> 'b t
Run a generator
val run : ?st:state -> 'a t -> 'a

Using a random state (possibly the one in argument) run a generator