type Rng = { state: UInt64 }
PRNG state. Copy it to fork a reproducible stream.
std/random
6 exports, from std/random.vyrn.
Deterministic pseudo-randomness with a host-seeded escape.
The generator is a value (Rng): each draw returns the value and the advanced Rng, so a seeded run reproduces on every engine. There is no ambient random(); randomSeed is the one host effect. The algorithm is SplitMix64. It is not cryptographic: use it for shuffles, sampling and tests, not for secrets. PRNG state. Copy it to fork a reproducible stream.
Dependencies
The import graph shows the whole library.
- Imports
- nothing else in std/
- Imported by
- storage
type Draw = { value: Int64, rng: Rng }
One draw: the value and the advanced generator.
fn randomSeed() -> Int64
An unpredictable seed from the host CSPRNG. A host effect, so generators and comptime code cannot call it.
fn seededRng(seed: Int64) -> Rng
A generator seeded by any Int64. SplitMix64 has no bad states, so the seed's bit pattern is the initial state.
fn nextInt(rng: Rng) -> Draw
Advances the generator once: value covers the full Int64 range. Pure, so generators and comptime code can call it.
fn nextInRange(rng: Rng, lo: Int64, hi: Int64) -> Draw
A draw in the inclusive range [lo, hi], or lo if the range is empty. Modulo reduction, so a very wide range has a slight low bias.
The span is UInt64 because hi - lo + 1 reaches 2^64. That wraps to 0, which means the full range: every draw lands inside it and the reduction is skipped.
Tests
2 test blocks in std/random.vyrn. CI runs all of them.
Test names
- nextInRange covers the full Int64 range without trapping
- nextInRange stays deterministic and in range on wide spans
Examples
1 program in examples/ import this module. Each runs as WebAssembly and as a native binary.