ioref_float.hs

module Example (main) where

import Data.IORef
import Data.Primitive
import Data.Primitive.PrimArray
import GHC.Prim (RealWorld)

main :: IO ()
main = do
  let len = 30
  arr <- newInitialise len
  modifyArray (+1) arr
  x <- readPrimArray arr (len `div` 2)
  print x 

newInitialise :: Int -> IO (MutablePrimArray RealWorld Int)
newInitialise sz = do
  arr <- newPrimArray sz
  let go :: Int -> IO ()
      go ix = if ix < sz
        then writePrimArray arr ix 0 >> go (ix + 1)
        else pure ()
  go 0
  pure arr

modifyArray :: (Int -> Int) -> MutablePrimArray RealWorld Int -> IO ()
modifyArray f arr = do
  let sz = sizeofMutablePrimArray arr
  let go :: Int -> IO () 
      go ix = if ix < sz
        then do
          atIx <- readPrimArray arr ix
          writePrimArray arr ix (f atIx)
          go (ix + 1)    
        else pure () 

  go 0
  
{-
  x <- newIORef 0
  add1 x
  v <- readIORef x
  print v  


add1 :: IORef Int -> IO ()
add1 x = modifyIORef' x (+1)

-}