Haskell Vectors

vector.hs

#!nix-shell --pure -p "haskellPackages.ghcWithPackages(pkgs:[pkgs.text pkgs.bytestring pkgs.vector])" -i runghc

{- |
haskell vectors
-}

import qualified Data.ByteString.Lazy.Char8 as C8Lazy
import qualified Data.Vector as V
import qualified Data.Vector.Mutable as MV
import qualified Data.Maybe as Maybe
import System.Environment
import Control.Monad.IO.Class (liftIO)

main :: IO ()
main = do
  [f] <- getArgs
  s <- C8Lazy.readFile f
  print . V.sum . parse $ s
  vectorImutable
  putStrLn "+++++++++++++++++++"
  vectorMutable

{- | fill the a vector with numbers from input file
-}
parse :: C8Lazy.ByteString -> V.Vector Int
parse  = V.unfoldr step
  where
    step !s = Maybe.maybe Nothing f (C8Lazy.readInt s)
    f = \(i, s) -> Just(i, C8Lazy.tail s)

vectorImutable :: IO ()
vectorImutable = do
  let v = V.fromList ['a' .. 'z']
  let e = v V.! 1
  let v1 = v V.//[(1, 'x')]
  let e1 = v1 V.! 1
  let v2 = V.slice 1 2 v1
  print e
  print e1
  print v2

vectorMutable :: IO ()
vectorMutable = do
  let v = V.fromList ['a' .. 'z']
  mvv <- liftIO $ V.thaw v
  MV.write mvv 1 'Z'
  v' <- V.freeze mvv
  print v'

This is a nix script. To execute:

chmod 755 ./vector.hs
seq 1 100000 >  ./data
./vector.hs data