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https://github.com/idris-lang/Idris2.git
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83 lines
2.4 KiB
Idris
83 lines
2.4 KiB
Idris
module System.Random
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import Data.Fin
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import Data.Vect
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import Data.List
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public export
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interface Random a where
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randomIO : HasIO io => io a
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||| Takes a range (lo, hi), and returns a random value uniformly
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||| distributed in the closed interval [lo, hi]. It is unspecified what
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||| happens if lo > hi.
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randomRIO : HasIO io => (a, a) -> io a
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%foreign "scheme:blodwen-random"
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"javascript:lambda:(max)=>Math.floor(Math.random() * max)"
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prim__randomBits32 : Bits32 -> PrimIO Bits32
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randomBits32 : Bits32 -> IO Bits32
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randomBits32 upperBound = fromPrim (prim__randomBits32 upperBound)
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public export
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Random Int32 where
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-- Generate a random value within [-2^31, 2^31-1].
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randomIO = do
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let maxInt : Bits32 = 2147483647 -- shiftL 1 31 - 1
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negMinInt : Bits32 = 2147483648 -- negate $ shiftL 1 31
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magnitude : Bits32 = maxInt + negMinInt
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bits32 <- liftIO $ randomBits32 magnitude
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let int : Integer = cast bits32
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pure . cast $ int - (cast negMinInt)
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-- Generate a random value within [lo, hi].
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randomRIO (lo, hi) =
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let range : Integer = (cast hi) - (cast lo) + 1
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in pure . cast $ !(liftIO . randomBits32 $ cast range) + cast lo
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%foreign "scheme:blodwen-random"
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"javascript:lambda:()=>Math.random()"
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prim__randomDouble : PrimIO Double
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randomDouble : IO Double
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randomDouble = fromPrim prim__randomDouble
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public export
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Random Double where
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-- 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
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export
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srand : Bits64 -> IO ()
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srand n = fromPrim (prim__srand n)
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||| Generate a random number in Fin (S `k`)
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||| Note that rndFin k takes values 0, 1, ..., k.
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public export
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rndFin : HasIO io => (n : Nat) -> io (Fin (S n))
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rndFin 0 = pure FZ
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rndFin (S k) = do
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let intBound = the Int32 (cast (S k))
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randomInt <- randomRIO (0, intBound)
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pure $ restrict (S k) (cast randomInt)
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||| Select a random element from a vector
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public export
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rndSelect' : HasIO io => {k : Nat} -> Vect (S k) a -> io a
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rndSelect' xs = pure $ Vect.index !(rndFin k) xs
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||| Select a random element from a non-empty list
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public export
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rndSelect : HasIO io => (elems : List a) -> (0 _ : NonEmpty elems) => io a
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rndSelect (x :: xs) = rndSelect' $ fromList (x :: xs)
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