Question

我正在尝试BetterPredicate.hs的{{1}}，关于ClockTime的代码段代码在我的ghc 7.6.3下引发错误：

    Couldn't match expected type `ClockTime'
            with actual type `time-1.4.0.1:Data.Time.Clock.UTC.UTCTime'

根据Hyogeol Lee对本书在线版"getModificationTime does not returns ClockTime type in ghc 7.6.3, but you can use UTCTime instead."的评论，在前奏提示下，我试过：+m Data.Time.Clock.UTC，我收到以下错误：

<no location info>:
Could not find module `Data.Time.Clock.UTC'
It is a member of the hidden package `time-1.4.0.1'.
it is a hidden module in the package `time-1.5'
it is a hidden module in the package `time-1.4.0.1'

ghc-pkg list time的结果是

ghc-pkg list time
/usr/lib64/ghc-7.6.3/package.conf.d
time-1.4.0.1
/home/abelard/.ghc/x86_64-linux-7.6.3/package.conf.d
time-1.5

但我仍然不知道该怎么办？

编辑：根据user2407038，我使用ghc-pkg unregister time-1.5删除时间1.5，之后我得到了类似的错误：

:m +Data.Time.Clock.UTC
Could not find module `Data.Time.Clock.UTC'
It is a member of the hidden package `time-1.4.0.1'.
it is a hidden module in the package `time-1.4.0.1'

和

Prelude> :m +Data.Time.Clock
<no location info>:
Could not find module `Data.Time.Clock'
It is a member of the hidden package `time-1.4.0.1'.

编辑2 ：在阅读了Real World Haskell's chapter 9的输出后，并更改了BetterPredicate.hs的代码： System.Time(ClockTime(..)) Data.Time.Clock(UTCTime) ghc --make BetterPredicate.hs -package time-1.4.0.1，以下两种方式对我有用：

编译文件BetterPredicate.hs：sudo ghc-pkg expose time-1.4.0.1
使用ghci取消隐藏，然后在Data.Time.Clock下，我可以成功加载模块:m +Data.Time.Clock：

*Main Data.Time.Clock> :t UTCTime

UTCTime :: time-1.4.0.1:Data.Time.Calendar.Days.Day -> DiffTime -> UTCTime

{{1}}

Answer 1

要修复RWH第9章中的BetterPredicate.hs模块，您必须执行以下操作：

import Data.Time.Clock
将Predicate的定义更改为使用UTCTime而不是ClockTime
从Control.Exception
定义handleAny函数
在handleAny和handle函数

saferFileSize

getFileSize

import Data.Time.Clock (UTCTime)
import Control.Exception (bracket, handle, SomeException)
...
type Predicate =  FilePath      -- path to directory entry
               -> Permissions   -- permissions
               -> Maybe Integer -- file size (Nothing if not file)
               -> UTCTime       -- last modified
               -> Bool
...
handleAny :: (SomeException -> IO a) -> IO a -> IO a
handleAny = handle
...
saferFileSize path = handleAny (\_ -> ...
...
getFileSize path = handleAny (\_ -> ...

固定代码在这里：http://lpaste.net/116709

它是`time-1.5＆＃39;包中的一个隐藏模块。跑步时＃34; ：load Data.Time.Clock.UTC＆＃34;

1 个答案: