mirror of
https://github.com/nim-lang/Nim.git
synced 2025-12-30 09:54:49 +00:00
43 lines
975 B
Nim
43 lines
975 B
Nim
discard """
|
|
output: "11.0"
|
|
"""
|
|
|
|
type
|
|
# A random number generator
|
|
Random = object
|
|
random: proc(): float
|
|
# A generic typeclass for a random var
|
|
RandomVar[A] = concept x
|
|
var rng: Random
|
|
rng.sample(x) is A
|
|
# A few concrete instances
|
|
Uniform = object
|
|
a, b: float
|
|
ClosureVar[A] = object
|
|
f: proc(rng: var Random): A
|
|
|
|
# How to sample from various concrete instances
|
|
proc sample(rng: var Random, u: Uniform): float = u.a + (u.b - u.a) * rng.random()
|
|
|
|
proc sample[A](rng: var Random, c: ClosureVar[A]): A = c.f(rng)
|
|
|
|
proc uniform(a, b: float): Uniform = Uniform(a: a, b: b)
|
|
|
|
# How to lift a function on values to a function on random variables
|
|
proc map[A, B](x: RandomVar[A], f: proc(a: A): B): ClosureVar[B] =
|
|
proc inner(rng: var Random): B =
|
|
f(rng.sample(x))
|
|
|
|
result.f = inner
|
|
|
|
import sugar
|
|
|
|
proc fakeRandom(): Random =
|
|
result.random = () => 0.5
|
|
|
|
let x = uniform(1, 10).map((x: float) => 2 * x)
|
|
|
|
var rng = fakeRandom()
|
|
|
|
echo rng.sample(x)
|