Basic random number generator support based on the one available on the Haskell library

class RandomGen (g : Type u) : Type u

Interface for random number generators.

• range : g → Nat × Nat

  range returns the range of values returned by the generator.

• next : g → Nat × g

  next operation returns a natural number that is uniformly distributed the range returned by range (including both end points), and a new generator.

• split : g → g × g

  The 'split' operation allows one to obtain two distinct random number generators. This is very useful in functional programs (for example, when passing a random number generator down to recursive calls).

structure StdGen : Type

"Standard" random number generator.

• s1 : Nat
• s2 : Nat

instance instInhabitedStdGen : Inhabited StdGen

def stdRange : Nat × Nat

The range of values returned by StdGen

instance instReprStdGen : Repr StdGen

def stdNext : StdGen → Nat × StdGen

The next value from a StdGen, paired with an updated generator state.

def stdSplit : StdGen → StdGen × StdGen

Splits a StdGen into two separate states.

instance instRandomGenStdGen : RandomGen StdGen

def mkStdGen (s : Nat := 0) : StdGen

Returns a standard number generator.

def randNat {gen : Type u} [RandomGen gen] (g : gen) (lo hi : Nat) : Nat × gen

Generates a random natural number in the interval [lo, hi].

def randBool {gen : Type u} [RandomGen gen] (g : gen) : Bool × gen

Generates a random Boolean.

opaque IO.stdGenRef : Ref StdGen

def IO.setRandSeed (n : Nat) : BaseIO Unit

Seeds the random number generator state used by IO.rand.

def IO.rand (lo hi : Nat) : BaseIO Nat

Returns a pseudorandom number between lo and hi, using and updating a saved random generator state.

This state can be seeded using IO.setRandSeed.