random

import "random" expose random

The module exposes a single ready-made random instance (of an internal Random class), seeded from the OS’s source of randomness by default:

class Random do
  this.__init__(self, seed) = do
    self.__state__ = __rand__.random_seed(seed)
  this.random(self) = do
    return __rand__.random_next_number(self.__state__)
  this.range(self, start, end) = do
    return start + self.random()*end
  this.int(self, start, end) = do
    return maths.int(self.range(start, end))
  this.choice(self, arr) = do
    return arr[self.int(0, arr.length)]

let random = Random(__rand__.random_os_seed())

(from stdlib/random/init.ar) — the underlying random number generation is implemented in native C (native/random.c), loaded via load_native_code.

Reference

Member	Description
random.random()	a random floating point number in [0, 1)
random.range(start, end)	a random float between start and end
random.int(start, end)	a random integer between start and end (inclusive-ish, see usage below)
random.choice(arr)	a random element from arr

Examples

Picking a random index and popping it (a shuffle pattern):

import "random" expose random

let x = []
let i = 0
while (i < 1e6) do
    x.append(i)
    i = i + 1

let y = []
while (x.length) do
    let result = x.pop(random.int(0, x.length - 1))
    y.append(result)

(from array_pop.ar)

Swapping random elements (Fisher–Yates style shuffle):

let random_index = random.int(0, len - 1)
let temp = x[len - 1]
x[len - 1] = x[random_index]
x[random_index] = temp

(from array_set.ar)

Creating your own generator

You can also construct your own seeded Random-like instance if you need reproducibility, though the standard library’s random export is a single shared instance seeded from the OS by default — check the random_test.ar test file in the repository if you need to see further custom-seeding examples.

Next

• path