mirror of
https://github.com/idris-lang/Idris2.git
synced 2024-12-18 16:51:51 +03:00
69 lines
1.9 KiB
Idris
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)
|