Stdlib.Random(3)

💖 Stdlib.Random(3) 💖

okay so this is the OCaml library manual page for Stdlib.Random, and bestie we are absolutely getting into it. ✨

✨ NAME ✨

Stdlib.Random — and the description is literally no description 😭. Minimalist. Iconic. No notes.

🦋 Module 🦋

Module Stdlib.Random

💖 Documentation 💖

Module Random : (module Stdlib__Random)

🌸 Basic functions 🌸

• val init : int -> unit — Initialize the domain-local generator, using the argument as a seed. The same seed will always yield the same sequence of numbers. Lowkey deterministic queen 💅
• val full_init : int array -> unit — Same as Random.init but takes more data as seed.
• val self_init : unit -> unit — Initialize the domain-local generator with a random seed chosen in a system-dependent way. If a cryptographically secure pseudorandom number generator is available on the host machine, it is used to provide a highly random initial seed. Otherwise, a less random seed is computed from system parameters (current time, process IDs, domain-local state).
• val bits : unit -> int — Return 30 random bits in a nonnegative integer.
• val int : int -> int — Random.int bound returns a random integer between 0 (inclusive) and bound (exclusive). bound must be greater than 0 and less than 2^30.

Raises Invalid_argument if bound <= 0 or bound >= 2^30.

• val full_int : int -> int — Random.full_int bound returns a random integer between 0 (inclusive) and bound (exclusive). bound may be any positive integer.

If bound is less than 2^31, then Random.full_int bound yields identical output across systems with varying int sizes.

If bound is less than 2^30, then Random.full_int bound is equal to Random.int bound.

If bound is at least 2^30 (on 64-bit systems, or non-standard environments such as JavaScript), then Random.full_int returns a value whereas Random.int raises Invalid_argument.

Since 4.13

Raises Invalid_argument if bound <= 0.

• val int_in_range : min:int -> max:int -> int — Random.int_in_range ~min ~max returns a random integer between min (inclusive) and max (inclusive). Both min and max are allowed to be negative; min must be less than or equal to max.

If both bounds fit in 32-bit signed integers (that is, if -2^31 <= min and max < 2^31), then int_in_range yields identical output across systems with varying int sizes.

Since 5.2

Raises Invalid_argument if min > max.

• val int32 : Int32.t -> Int32.t — Random.int32 bound returns a random integer between 0 (inclusive) and bound (exclusive). bound must be greater than 0.

Raises Invalid_argument if bound <= 0.

• val int32_in_range : min:int32 -> max:int32 -> int32 — Random.int32_in_range ~min ~max returns a random integer between min (inclusive) and max (inclusive). Both min and max are allowed to be negative; min must be less than or equal to max.

Since 5.2

Raises Invalid_argument if min > max.

• val nativeint : Nativeint.t -> Nativeint.t — Random.nativeint bound returns a random integer between 0 (inclusive) and bound (exclusive). bound must be greater than 0.

Raises Invalid_argument if bound <= 0.

• val nativeint_in_range : min:nativeint -> max:nativeint -> nativeint — Random.nativeint_in_range ~min ~max returns a random integer between min (inclusive) and max (inclusive). Both min and max are allowed to be negative; min must be less than or equal to max.

Since 5.2

Raises Invalid_argument if min > max.

• val int64 : Int64.t -> Int64.t — Random.int64 bound returns a random integer between 0 (inclusive) and bound (exclusive). bound must be greater than 0.

Raises Invalid_argument if bound <= 0.

• val int64_in_range : min:int64 -> max:int64 -> int64 — Random.int64_in_range ~min ~max returns a random integer between min (inclusive) and max (inclusive). Both min and max are allowed to be negative; min must be less than or equal to max.

Since 5.2

Raises Invalid_argument if min > max.

• val float : float -> float — Random.float bound returns a random floating-point number between 0 and bound (inclusive). If bound is negative, the result is negative or zero. If bound is 0, the result is 0.
• val bool : unit -> bool — Random.bool () returns true or false with probability 0.5 each.
• val bits32 : unit -> Int32.t — Random.bits32 () returns 32 random bits as an integer between Int32.min_int and Int32.max_int.

Since 4.14

• val bits64 : unit -> Int64.t — Random.bits64 () returns 64 random bits as an integer between Int64.min_int and Int64.max_int.

Since 4.14

• val nativebits : unit -> Nativeint.t — Random.nativebits () returns 32 or 64 random bits (depending on the bit width of the platform) as an integer between Nativeint.min_int and Nativeint.max_int.

Since 4.14

🧚 Advanced functions 🧚

The functions from module Random.State manipulate the current state of the random generator explicitly. This allows using one or several deterministic PRNGs, even in a multi-threaded program, without interference from other parts of the program.

module State : sig end

• val get_state : unit -> State.t — get_state() returns a fresh copy of the current state of the domain-local generator (which is used by the basic functions).

The current state is unchanged, which means that random numbers generated from multiple calls to get_state () will be identical.

See Random.State.make_self_init and Random.split instead to obtain a fresh state that is not shared.

• val set_state : State.t -> unit — set_state s updates the current state of the domain-local generator (which is used by the basic functions) by copying the state s into it.
• val split : unit -> State.t — Draw a fresh PRNG state from the current state of the domain-local generator used by the default functions. (The state of the domain-local generator is modified.) See Random.State.split.

Since 5.0

---

Source/version: OCamldoc · date: 2026-06-22 · page: Stdlib.Random(3). Bye bestie, go generate something cute 💅✨