Mutable vectors

[chris-martin]

Here's an example I jotted down a while ago. A slightly more practical example might be nice, but I don't think I've ever actually used mutable vectors in Haskell, nothing is immediately coming to mind... ideas welcome.

import qualified Data.Vector as V
import qualified Data.Vector.Mutable as MV

main =
  do
    a <- MV.replicate 5 0
    do a' <- V.freeze a; putStrLn ("empty: " ++ show a')

    MV.write a 4 100
    do a' <- V.freeze a; putStrLn ("write: " ++ show a')
    do x <- MV.read a 4; putStrLn ("read: " ++ show x)

    putStrLn ("length: " ++ show (MV.length a))

    b <- V.thaw (V.fromList [1..5])
    do b' <- V.freeze b; putStrLn ("dcl: " ++ show b')

$ runhaskell vectors.hs
empty: [0,0,0,0,0]
write: [0,0,0,0,100]
read: 100
length: 5
dcl: [1,2,3,4,5]

[cideM]

Added PR for this one #33