Question

实施getReturnList和getReturnList2

getReturnList用于计算一次返回a/b

getReturnList2用于高级版本并行使用分而治之以增加计算返回a/b的速度意味着它想要以不同方式并行计算整个列表的子列表

第一个错误我不明白我将x : []传递给参数[String] 编译器返回此错误

error for getReturnList

    readcsv.hs:108:20:
        Couldn't match type `Char' with `[Char]'
        Expected type: [String]
          Actual type: String
        In the return type of a call of `getClose'
        In the first argument of `(:)', namely `(getClose (x : []))'
        In the expression:
          (getClose (x : [])) : getReturnList (n - 1) total xs

    readcsv.hs:108:30:
        Couldn't match type `[Char]' with `Char'
        Expected type: String
          Actual type: [String]
        In the first argument of `(:)', namely `x'
        In the first argument of `getClose', namely `(x : [])'
        In the first argument of `(:)', namely `(getClose (x : []))'

代码：

import Control.Monad.Par
import Text.ParserCombinators.Parsec
import Data.Either.Unwrap
import System.IO
{- A CSV file contains 0 or more lines, each of which is terminated
   by the end-of-line character (eol). -}
csvFile :: GenParser Char st [[String]]
csvFile = 
    do result <- many line
       eof
       return result

-- Each line contains 1 or more cells, separated by a comma
line :: GenParser Char st [String]
line = 
    do result <- cells
       eol                       -- end of line
       return result

-- Build up a list of cells.  Try to parse the first cell, then figure out 
-- what ends the cell.
cells :: GenParser Char st [String]
cells = 
    do first <- cellContent
       next <- remainingCells
       return (first : next)

-- The cell either ends with a comma, indicating that 1 or more cells follow,
-- or it doesn't, indicating that we're at the end of the cells for this line
remainingCells :: GenParser Char st [String]
remainingCells =
    (char ',' >> cells)            -- Found comma?  More cells coming
    <|> (return [])                -- No comma?  Return [], no more cells

-- Each cell contains 0 or more characters, which must not be a comma or
-- EOL
cellContent :: GenParser Char st String
cellContent = 
    many (noneOf ",\n")


-- The end of line character is \n
eol :: GenParser Char st Char
eol = char '\n'

parseCSV :: String -> Either ParseError [[String]]
--parseCSV :: String -> [[String]]
--parseCSV input = parse csvFile input
parseCSV input = parse csvFile "(unknown)" input


take3 :: Int ->[[String]] -> [String]
take3 0 _ = []
take3 _ [] = []
take3 n (x:xs) 
    | n == 1 = x
    | n > 0 = take3 (n-1) xs
take3 _ _ = error "preludelist.take: negative argument"

returnlimiters = ['\n']


realtake2 :: Int -> [[String]] -> [String]
realtake2 x y = take3 x y

takeelem3 :: Int -> [String] -> String
takeelem3 0 _ = []
takeelem3 _ [] = []
takeelem3 n (x:xs) 
    | n == 1 = x
    | n > 0 = takeelem3 (n-1) xs
takeelem3 _ _ = error "preludelist.take: negative argument"


realtakeelem2 :: Int -> [String] -> String
realtakeelem2 x y = takeelem3 x y


getOpen :: [String] -> String
getOpen x = realtakeelem2 2 x

getHigh :: [String] -> String
getHigh x = realtakeelem2 3 x

getLow :: [String] -> String
getLow x = realtakeelem2 4 x

getClose :: [String] -> String
getClose x = realtakeelem2 5 x


whitespace :: String
whitespace = ['\n','\t',' ']


forloop3 0 f = return()
forloop3 n f =
 do
  f n
  forloop3 (n-1) f


getReturnList :: Int -> Int -> [[String]] -> [[String]]
getReturnList 0 _ _ = []
getReturnList _ _ [] = []
getReturnList n total (x:xs) 
    | n == total = getReturnList (n-1) total xs
    | n > 0 = (getClose (x : [])) : getReturnList (n-1) total xs
getReturnList _ _ _ = error "preludelist.take: negative argument"


getReturnList2 :: Int -> Int -> [[String]] -> [[String]]
getReturnList2 0 _ _ = []
getReturnList2 _ _ [] = []
getReturnList2 n total (x:xs) 
    | n == total = getReturnList2 (n-1) total xs
    | n > 0 = 
           do
             p1 <- spawn (getReturnList2 n-1 total (filter (<x) xs))
             p2 <- spawn (getReturnList2 n-1 total (filter (>=x) xs))
             left <- get p1
             right <- get p2
             return $ left ++ (x:right)
getReturnList2 _ _ _ = error "preludelist.take: negative argument"



main = do
    csvstring <- readFile "C:\\Users\\martin.lee\\Downloads\\0388.HK.csv"
    let afterparse = parseCSV csvstring

    let afterparse2 = fromRight afterparse
    --putStrLn(show afterparse2)
    let getline3 = realtake2 3 afterparse2
    putStrLn(show getline3)
    --putStrLn(getOpen getline3)
    --putStrLn(getHigh getline3)
    --putStrLn(getLow getline3)
    putStrLn(getClose getline3) 
    --forloop3 5 (\c -> putStrLn(show (5-c)))

    --putStrLn(show (take2b 3 2 3 afterparse2))
    --let (as,bs) = splitAt (length grids `div` 2) afterparse2


    let num = 5

    putStrLn("begin getReturnList")
    putStrLn(show ( "a" : []))
    putStrLn(show (getReturnList 3 3 afterparse2))
    putStrLn("end getReturnList")
    --putStrLn(show (1 :: Float))
    --putStrLn(show (getlines2 csvstring))
    --putStrLn(show (take 1 (getlines2 csvstring)))
    putStrLn("a")

更新

F＃非并行版

let rec test2(xs : float list) =
        if xs.Length > 3 then
            let (list1, list2) = split1 (xs.Length/2) xs
            let (list3, list4) = split1 (xs.Length/2-1) xs
            let b1 = test2(list1) // would like to parallel these two function
            let b2 = test2(list4) // would like to parallel these two function
            b1 @ b2
        else
            let b1 = xs |> Seq.windowed 2
                        |> PSeq.map (fun x -> x.[0]/x.[1])
                        |> PSeq.toList
            b1

如何并行使用分而治之以计算a / b作为此列表的返回值

0 个答案: