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Idris2/libs/contrib/System/Random.idr

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module System.Random
import Data.Fin
import Data.Vect
import Data.List
public export
interface Random a where
randomIO : HasIO io => io a
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-- 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 : HasIO io => (a, a) -> io a
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%foreign "scheme:blodwen-random"
prim__randomInt : Int -> PrimIO Int
randomInt : Int -> IO Int
randomInt upperBound = fromPrim (prim__randomInt upperBound)
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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
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in map (+ minInt) $ liftIO $ randomInt range
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-- Generate a random value within [lo, hi].
randomRIO (lo, hi) =
let range = hi - lo + 1
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in map (+ lo) $ liftIO $ randomInt range
%foreign "scheme:blodwen-random"
prim__randomDouble : PrimIO Double
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randomDouble : IO Double
randomDouble = fromPrim prim__randomDouble
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public export
Random Double where
-- Generate a random value within [0, 1].
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randomIO = liftIO randomDouble
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-- Generate a random value within [lo, hi].
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randomRIO (lo, hi) = map ((+ lo) . (* (hi - lo))) (liftIO randomDouble)
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%foreign "scheme:blodwen-random-seed"
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prim__srand : Bits64 -> PrimIO ()
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||| Sets the random seed
export
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srand : Bits64 -> IO ()
srand n = fromPrim (prim__srand n)
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||| 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)