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|
-- 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 ()
|
