小编wil*_*y-s的帖子

我最初编写了一个功能强力搜索(城市的ADT表示,城市的元组作为距离数组的索引,懒惰地产生排列Data.List.permutations并使用严格的左折叠消耗它们),但这非常缓慢.我设法通过以更迫切的方式连续重写它并使用Heap的算法进行排列来加速它3倍,但直接将结果转换为(写得不好)C再快10倍!到底是怎么回事？

{-# LANGUAGE TupleSections, BangPatterns, ForeignFunctionInterface #-}

import Data.Array.Unboxed
import Data.Array.Base (unsafeAt)
import qualified Data.Vector.Unboxed.Mutable as M
import qualified Data.Vector.Unboxed as V
import Data.Word (Word)
import Data.IORef
import GHC.Arr (Ix(..)) 
import Control.Arrow
import Control.Monad

import Data.Array.Storable
import Foreign.Ptr (Ptr)
import Foreign.C (CInt)

import Criterion.Main

distances :: UArray Int Word
distances = listArray (0, 255) [0,629,1023,1470,1276,915,894,1199,760,795,676,903,1394,350,647,922,629,
                                0,556,1312,674,1097,317,946,784,504,1228,276,1254,878,712,1236,1023,556,
                                0,861,408,977,280,480,1340,288,1424,533,822,1346,1267,1198,1470,1312,861,
                                0,1196,751,1125,382,2052,809,1476,1381,78,1817,1957,980,1276,674,408,1196,
                                0,1384,383,837,1370,676,1777,469,1173,1551,1327,1600,915,1097,977,751,1384,
                                0,1103,722,1641,719,730,1303,676,1223,1530,249,894,317,280,1125,383,1103,
                                0,743,1083,392,1409,256,1079,1178,1019,1293,1199,946,480,382,837,722,743,
                                0,1708,454,1366,999,343,1549,1618,972,760,784,1340,2052,1370,1641,1083,1708,
                                0,1253,1392,901,1986,640,113,1679,795,504,288,809,676,719,392,454,1253,
                                0,1138,623,749,1136,1164,925,676,1228,1424,1476,1777,730,1409,1366,1392,1138,
                                0,1502,1399,786,1283,551,903,276,533,1381,469,1303,256,999,901,623,1502,
                                0,1335,1127,857,1469,1394,1254,822,78,1173,676,1079,343,1986,749,1399,1335,
                                0,1741,1889,908,350,878,1346,1817,1551,1223,1178,1549,640,1136,786,1127,1741,
                                0,543,1182,647,712,1267,1957,1327,1530,1019,1618,113,1164,1283,857,1889,543,
                                0,1566,922,1236,1198,980,1600,249,1293,972,1679,925,551,1469,908,1182,1566,0]

tsp_mut :: [Int] -> IO ([Int], Word) 
tsp_mut [] …

我正在尝试编写一些win32包中未包含的win32 API函数的绑定,但遇到了一些困难.在下面的代码中,EnumWindows和GetWindow的绑定工作正常,但GetWindowText和GetWindowTextLength的绑定不能:

{-# LANGUAGE ForeignFunctionInterface #-}

import Foreign.Ptr
import Graphics.Win32.GDI.Types (HWND)
import System.Win32.Types (ptrToMaybe)
import Foreign.C
import Foreign.Marshal.Alloc (free)
import Control.Applicative ((<$>))

gW_CHILD = 5::CInt

getWindow :: HWND -> CInt -> IO (Maybe HWND)
getWindow hwnd cint = ptrToMaybe <$> (c_getWindow hwnd cint)
foreign import stdcall "windows.h GetWindow"
  c_getWindow :: HWND -> CInt -> IO HWND

foreign import stdcall "windows.h EnumWindows"
  enumWindows :: (FunPtr (HWND -> Ptr b -> IO a)) -> CInt -> IO CInt  

foreign import stdcall "windows.h …