Module Base.Random

Pseudo-random number generation.

This is a wrapper of the standard library's Random library, though it does not share state with that library.

Basic functions

Note that all of these "basic" functions mutate a global random state.

val init : int -> unit

Initialize the generator, using the argument as a seed. The same seed will always yield the same sequence of numbers.

val full_init : int array -> unit

Same as Random.init but takes more data as seed.

val self_init : ?allow_in_tests:bool -> unit -> unit

Initialize the generator with a more-or-less random seed chosen in a system-dependent way. By default, self_init is disallowed in inline tests, as it's often used for no good reason and it just creates nondeterministic failures for everyone. Passing ~allow_in_tests:true removes this restriction in case you legitimately want nondeterministic values, like in Filename.temp_dir.

val bits : unit -> int

Return 30 random bits in a nonnegative integer.

  • before 3.12.0

    used a different algorithm (affects all the following functions)

val int : int -> int

Random.int bound returns a random integer between 0 (inclusive) and bound (exclusive). bound must be greater than 0.

val int32 : int32 -> int32

Random.int32 bound returns a random integer between 0 (inclusive) and bound (exclusive). bound must be greater than 0.

val nativeint : nativeint -> nativeint

Random.nativeint bound returns a random integer between 0 (inclusive) and bound (exclusive). bound must be greater than 0.

val int64 : int64 -> int64

Random.int64 bound returns a random integer between 0 (inclusive) and bound (exclusive). bound must be greater than 0.

val float : float -> float

Random.float bound returns a random floating-point number between 0 (inclusive) and bound (exclusive). If bound is negative, the result is negative or zero. If bound is 0, the result is 0.

val int_incl : int -> int -> int

Produces a random value between the given inclusive bounds. Raises if bounds are given in decreasing order.

val int32_incl : int32 -> int32 -> int32
val nativeint_incl : nativeint -> nativeint -> nativeint
val int64_incl : int64 -> int64 -> int64
val float_range : float -> float -> float

Produces a value between the given bounds (inclusive and exclusive, respectively). Raises if bounds are given in decreasing order.

val bool : unit -> bool

Random.bool () returns true or false with probability 0.5 each.

val char : unit -> char

Return a uniformly-chosen char.

val ascii : unit -> char

Return a uniformly-chosen char in the ASCII range.

Advanced functions
module State : sig ... end

The functions from module 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.

val set_state : State.t -> unit

Sets the state of the generator used by the basic functions.