{-# LANGUAGE ScopedTypeVariables #-}
module Main where
import Control.Monad.ST
import Data.Primitive
main :: IO ()
main = do
let xs :: [Float] = runST $ do
barr <- mutableByteArrayFromList [1..fromIntegral n::Float]
peekByteArray n barr
print xs
where
n = 13
mutableByteArrayFromList :: forall s a . (Prim a)
=> [a]
-> ST s (MutableByteArray s)
mutableByteArrayFromList xs = do
arr <- newByteArray (length xs*sizeOf (undefined :: a))
loop arr 0 xs
return arr
where
loop :: (Prim a) => MutableByteArray s -> Int -> [a] -> ST s ()
loop _ _ [] = return ()
loop arr i (x : xs) = do
writeByteArray arr i x
loop arr (i+1) xs
peekByteArray :: (Prim a)
=> Int
-> MutableByteArray s
-> ST s [a]
peekByteArray n arr =
loop 0 arr
where
loop :: (Prim a)
=> Int
-> MutableByteArray s
-> ST s [a]
loop i _ | i >= n = return []
loop i arr = do
x <- readByteArray arr i
xs <- loop (i+1) arr
return (x : xs)