我的计时器总是返回0 [英] My timer always returns 0

问题描述

我在haskell中创建了一个计时器。问题是，它总是返回0.我认为这是因为懒惰，但我不知道如何解决它。

  import System.CPUTime 
 timeit :: IO（） - > IO（Float）
 timeit io = do 
 start< -getCPUTime 
 action< -seq start io 
结束< -seq动作getCPUTime 
返回$！ （fromIntegral $ end-start）/（10 ** 12）
  

正如您所见，我拥有抛出 seq 和 $！ galor，但无济于事。我在做什么？

在一个示例运行中：

  *主> timeit测试
你叫什么名字？ 
 Haskell 
您的名字是Haskell。 
 0.0 
  

解决方案

工作

  import Data.Time.Clock 
 
 timeit :: IO（） - > IO NominalDiffTime 
 timeit doit = do 
 start<  -  getCurrentTime 
 doit 
 end<  -  getCurrentTime 
 return（diffUTCTime end start）
  
 
 $ b 
现在进行一些讨论 -   
 
 
 
 
 
从评论看来，你想要的是实时，而不是cpu时间，所以这就是我写的。
      System.Time库不推荐使用，所以我把你切换到了Data.Time库。  
 
 
 NominalDiffTime保存时间，以秒为单位... 
 
 
 NominalDiffTime忽略闰秒！如果在程序运行期间增加了闰秒，10秒延迟将显示为11秒。我搜索了如何解决这个问题，尽管Data.Time确实有一个DiffTime类型来解决这个问题，但似乎没有一种简单的方法可以根据UTCTime生成DiffTime。我想你可能可以使用Posix时间库，从1970年1月1日开始获得秒数......然后拿这个差异，但这看起来像是为了一个非常罕见的bug而喋喋不休。但是，如果您正在编写软件来安全降落飞机，请深入挖掘并修复此问题。 ：） 
 
 
I have created a timer in haskell. The problem is, it always returns 0. I think this is because of laziness, but I do not know how to fix it.
import System.CPUTime
timeit::IO ()->IO (Float)
timeit io=do
    start  <-getCPUTime
    action <-seq start io
    end    <-seq action getCPUTime
    return $! (fromIntegral $ end-start)/(10**12)
As you can see, I have throw in seq and $! galor, but to no avail. What do I do?


Here in an example run:
*Main> timeit test
What is your name?
Haskell
Your name is Haskell.
0.0

解决方案
Here is some code I got to work
import Data.Time.Clock

timeit::IO ()->IO NominalDiffTime
timeit doit=do
    start  <- getCurrentTime
    doit
    end    <- getCurrentTime
    return (diffUTCTime end start)
Now for some discussion-

From the comments it seemed that you wanted real time, not cpu time, so that is what I wrote.
The System.Time libary is deprecated, so I switched you to the Data.Time library.
NominalDiffTime holds the time in seconds....
NominalDiffTime ignores leap seconds!  In the unlikely event that a leap second is added during the running of the program, a 10 second delay will show up as 11 seconds.  I googled around on how to fix this, and although Data.Time does have a DiffTime type to account for this, there doesn't seem to be a simple way to generate a DiffTime from UTCTime.  I think you may be able to use the Posix time libraries and get seconds from Jan 1, 1970....  Then take the diff, but this seems like to much hastle for a pretty rare bug.  If you are writing software to safely land airplanes however, please dig a bit deeper and fix this problem. :)


                        
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