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mirror of https://github.com/idris-lang/Idris2.git synced 2024-12-21 10:41:59 +03:00
Idris2/libs/contrib/System/Random.idr
2020-05-18 14:00:08 +01:00

69 lines
1.9 KiB
Idris

module System.Random
import Data.Fin
import Data.Vect
import Data.List
public export
interface Random a where
randomIO : IO a
-- Takes a range (lo, hi), and returns a random value uniformly
-- distributed in the closed interval [lo, hi]. It is unspecified what
-- happens if lo > hi.
randomRIO : (a, a) -> IO a
prim_randomInt : Int -> IO Int
prim_randomInt upperBound = schemeCall Int "blodwen-random" [upperBound]
public export
Random Int where
-- Generate a random value within [-2^31, 2^31-1].
randomIO =
let maxInt = shiftL 1 31 - 1
minInt = negate $ shiftL 1 31
range = maxInt - minInt
in map (+ minInt) $ prim_randomInt range
-- Generate a random value within [lo, hi].
randomRIO (lo, hi) =
let range = hi - lo + 1
in map (+ lo) $ prim_randomInt range
prim_randomDouble : IO Double
prim_randomDouble = schemeCall Double "blodwen-random" []
public export
Random Double where
-- Generate a random value within [0, 1].
randomIO = prim_randomDouble
-- Generate a random value within [lo, hi].
randomRIO (lo, hi) = map ((+ lo) . (* (hi - lo))) prim_randomDouble
||| Sets the random seed
export
srand : Integer -> IO ()
srand n = schemeCall () "blodwen-random-seed" [n]
||| Generate a random number in Fin (S `k`)
|||
||| Note that rndFin k takes values 0, 1, ..., k.
public export
rndFin : (n : Nat) -> IO (Fin (S n))
rndFin 0 = pure FZ
rndFin (S k) = do
let intBound = the Int (cast (S k))
randomInt <- randomRIO (0, intBound)
pure $ restrict (S k) (cast randomInt)
||| Select a random element from a vector
public export
rndSelect' : {k : Nat} -> Vect (S k) a -> IO a
rndSelect' {k} xs = pure $ Vect.index !(rndFin k) xs
||| Select a random element from a non-empty list
public export
rndSelect : (elems : List a) -> {auto prf : NonEmpty elems} -> IO a
rndSelect (x :: xs) {prf = IsNonEmpty} = rndSelect' $ fromList (x :: xs)