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(.module:
[lux #*
["_" test (#+ Test)]
[abstract
[monad (#+ do)]]
[data
["." product]
["." maybe ("#@." functor)]
[number
["n" nat]]
[collection
["." list ("#@." fold)]]]
[math
["." random (#+ Random)]]]
{1
["." /]})
(def: #export test
Test
(let [limit (: (Random Nat)
(:: random.monad map (n.% 20) random.nat))]
(do random.monad
[start limit
end limit
#let [[start end] (if (n.< end start)
[start end]
[end start])
range (/.range n.enum start end)]]
(<| (_.covering /._)
($_ _.and
(_.cover [/.range]
(let [expected-size (|> end (n.- start) inc)
expected-start? (|> range list.head (maybe@map (n.= start)) (maybe.default false))
expected-end? (|> range list.last (maybe@map (n.= end)) (maybe.default false))
every-element-is-a-successor? (case range
(#.Cons head tail)
(|> (list@fold (function (_ next [verdict prev])
[(and verdict
(n.= next (:: n.enum succ prev)))
next])
[true head]
tail)
product.left)
#.Nil
false)]
(and (n.= expected-size (list.size range))
expected-start?
expected-end?
every-element-is-a-successor?)))
)))))
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