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haskell - GHCI 无法加载“System.Time”的接口

问题描述

我正在学习 Haskell 并尝试从书中构建一个示例。当我在 GHCI 中使用“:l BetterPredicate”命令加载代码时，出现以下错误：

Prelude> :l BetterPredicate
[1 of 2] Compiling RecursiveContents ( RecursiveContents.hs, interpreted )

RecursiveContents.hs:12:32: warning: [-Wtabs]
    Tab character found here.
    Please use spaces instead.
[2 of 2] Compiling Main             ( BetterPredicate.hs, interpreted )

BetterPredicate.hs:3:1: error:
    Failed to load interface for ‘System.Time’
    Perhaps you meant
      System.CPUTime (from base-4.9.1.0)
      System.Cmd (from process-1.4.3.0)
      System.Mem (from base-4.9.1.0)
    Use -v to see a list of the files searched for.
Failed, modules loaded: RecursiveContents.

这是我要编译的代码：

import Control.Monad (filterM)
import System.Directory (Permissions (..), getModificationTime, getPermissions)
import System.Time (ClockTime(..))
import System.FilePath (takeExtension)
import Control.Exception (bracket, handle)
import System.IO (IOMode(..), hClose, hFileSize, openFile)

-- Our functions
import RecursiveContents (getRecursiveContents)

type Predicate = FilePath        -- Path to directory entry
              -> Permissions     -- permissions
              -> Maybe Integer   -- file size (Nothing if not file)
              -> ClockTime       -- last modified
              -> Bool
-- TBD
getFileSize :: FilePath -> IO (Maybe Integer)

betterFind :: Predicate -> FilePath -> IO [FilePath]
betterFind p path = getRecursiveContents >>= filterM check
    where check name = do 
              perms <- getPermissions name
              size  <- getFileSize name
              modified <- getModificationTime name 
              return (p name perms size modified)

simpleFileSize :: FilePath -> IO Integer
simpleFileSize path = do
    h <- openFile path ReadMode
    size <- hFileSize h
    hClose
    return size

saferFileSize :: FilePath -> IO (Maybe Integer)
saferFileSize path = handle (\_ -> return Nothing) $ do
    h <- openFile path ReadMode
    size <- hFileSize h
    hClose
    return (Just size)

getFileSize :: FilePath -> IO (Maybe Integer)
getFileSize path = handle (\_ -> return Nothing) $
    bracket (openFile path ReadOnly) hClose $ \h -> do
        size <- hFileSize h
        hClose
        return (Just size)


type InfoP a =  FilePath       -- path to directory entry
             -> Permissions    -- permissions
             -> Maybe Integer  -- file size (Nothing if not file)
             -> ClockTime      -- last modified
             -> a 

pathP :: InfoP FilePath
pathP path _ _ _ = path

sizeP :: InfoP Integer
sizeP _ _ (Just size) _ = size
sizeP _ _ Nothing     _ = -1

equalP :: (Eq a) => InfoP a -> a -> InfoP Bool
--equalP f k = \w x y z -> f w x y z == k
equalP f k w x y z = f w x y z == k

根据文档：http ://hackage.haskell.org/package/old-time-1.1.0.3/docs/System-Time.html这个模块是旧库的一部分，所以我想我需要导入它不知何故，但如果我不使用 Cabal（没有 *.cabal 文件）或其他东西构建包，我不知道该怎么做，我只想在 GHCI 中使用我的代码。

标签： haskellhaskell-platform

解决方案

只需用于cabal install全局安装包

$ cabal install old-time

它会给你一个警告，但如果你只是将它用于 ghci 支持，那也没关系。

另请注意文档警告：

Data.Time该库已弃用，请改为查看time 包。

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