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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)
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