-- use of vectorMapM
--

-------------------------------------------

import Data.Packed.Vector
import Numeric.LinearAlgebra.Interface

import Control.Monad.State

-------------------------------------------

-- an instance of MonadIO, a monad transformer
type VectorMonadT = StateT Int IO

v :: Vector Int
v = fromList $ take 10 [0..]

test1 :: Vector Int -> IO (Vector Int)
test1 = do
        mapVectorM (\x -> do
                          putStr $ (show x) ++ " "
                          return (x + 1))
                            
-- we can have an arbitrary monad AND do IO
addInitialM :: Vector Int -> VectorMonadT ()
addInitialM = mapVectorM_ (\x -> do
                                 i <- get
                                 liftIO $ putStr $ (show $ x + i) ++ " "
                                 put $ x + i
                          )

-- sum the values of the even indiced elements
sumEvens :: Vector Int -> Int
sumEvens = foldVectorWithIndex (\x a b -> if x `mod` 2 == 0 then a + b else b) 0 

-- sum and print running total of evens
sumEvensAndPrint :: Vector Int -> VectorMonadT ()
sumEvensAndPrint = mapVectorWithIndexM_ (\ i x -> do
                                                  when (i `mod` 2 == 0) (do
                                                                         v <- get
                                                                         put $ v + x
                                                                         v' <- get
                                                                         liftIO $ putStr $ (show v') ++ " " 
                                                                         return ())
                                                  return ()
                                        )

indexPlusSum :: Vector Int -> VectorMonadT ()
indexPlusSum v' = do
                  v <- mapVectorWithIndexM (\i x -> do
                                                    s <- get
                                                    let inc = x+s
                                                    liftIO $ putStr $ show (i,inc) ++ " "
                                                    put inc
                                                    return inc) v'
                  liftIO $ do
                           putStrLn ""
                           putStrLn $ show v

-------------------------------------------

main = do
       v' <- test1 v
       putStrLn ""
       putStrLn $ show v'
       evalStateT (addInitialM v) 0
       putStrLn ""
       putStrLn $ show (sumEvens v)
       evalStateT (sumEvensAndPrint v) 0
       putStrLn ""
       evalStateT (indexPlusSum v) 0
       return ()