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# bug #3995
import future
type
RNG* = tuple[]
Rand*[A] = (RNG) -> (A, RNG)
proc nextInt*(r: RNG): (int, RNG) =
(1, ())
proc flatMap[A,B](f: Rand[A], g: A -> Rand[B]): Rand[B] =
(rng: RNG) => (
let (a, rng2) = f(rng);
let g1 = g(a);
g1(rng2)
)
proc map[A,B](s: Rand[A], f: A -> B): Rand[B] =
let g: A -> Rand[B] = (a: A) => ((rng: RNG) => (f(a), rng))
flatMap(s, g)
let f = nextInt.map(i => i - i mod 2)
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