小编wen*_*ong的帖子

在项目pandoc中,Paths_pandoc在Shared.hs中导入.Paths_pandoc.hs位于dist/build/autogen /中.它是如何生成的以及它对pandoc的作用.

我使用的是带有语言环境zh_CN和ghc-7.0.4的Windows 7

cmd.exe的默认代码页是936.

> cabal install ghc-mod
Resolving dependencies...
Configuring ghc-syb-utils-0.2.1.0...
Preprocessing library ghc-syb-utils-0.2.1.0...
Building ghc-syb-utils-0.2.1.0...

<built-in>:0:4: lexical error (UTF-8 decoding error)
cabal: Error: some packages failed to install:
ghc-mod-1.10.7 depends on ghc-syb-utils-0.2.1.0 which failed to install.
ghc-syb-utils-0.2.1.0 failed during the building phase. The exception was:
ExitFailure 1

我已尝试更改代码页并重新安装,但获得相同的输出.

> chcp 65001
> cabal install ghc-mod

一些包可以成功构建:

xml-1.3.12 textmath-0.6.0.3 tagsoup-0.12.6

有些包会失败:

temporary-1.1.2.3 utf8-string-0.3.7 pandoc-types-1.9.0.2 json-0.5

这是一种表示现实世界物理单位的数据类型:

import qualified Prelude as P
import Prelude hiding ((+), (*), (/), (-), Int, pi)

data Int = Zero | Succ Int | Pred Int

data Unit :: Int -> Int -> Int -> * where
    U :: Double -> Unit m s kg

(+) :: Unit m s kg -> Unit m s kg -> Unit m s kg
(-) :: Unit m s kg -> Unit m s kg -> Unit m s kg
(*) :: Unit m1 …

在map之后和reduce之前,有一个排序阶段.在流模式下,hadoop如何知道您的密钥类型是什么,并对其进行排序.

例如

输入文件格式

1990    1
1991    4
1992    5
...

地图的结果有钥匙1990,1991,1992 ......,怎么用hadoop排序呢？(数字排序或字母排序)

import Text.JSON
import Control.Monad

data Status = Status { user :: String, text :: String } deriving Show

makeStatus :: JSObject JSValue -> Result Status
makeStatus tweet = let (!) = flip valFromObj in do
    userObject <- tweet ! "user"
    user <- userObject ! "screen_name"
    text <- tweet ! "text"
    return Status {user = user, text = text}

[1 of 1] Compiling Main             ( twitter.hs, interpreted )

twitter.hs:11:27:
    Couldn't match expected type `[Char]'
                with actual type `JSObject JSValue'
    Expected type: …

我尝试在GHCi中运行来自http://gregorycollins.net/posts/2011/10/01/cufp2011/index.html#(43)的代码,但得到了"浮点异常,GHCi退出.

{-# LANGUAGE OverloadedStrings #-}

import           Control.Applicative
import           Data.Aeson
import           Data.Attoparsec (parseOnly)
import           Data.ByteString.Char8  (ByteString)
import qualified Data.ByteString.Char8 as S
import qualified Data.ByteString.Lazy.Char8 as L


------------------------------------------------------------------------------
example1 :: ByteString -> Either String Coord
example1 bs = parseOnly json bs >>= convert
  where
    convert value = case fromJSON value of
                      (Error e)   -> Left e
                      (Success a) -> Right a

example2 :: Coord -> ByteString
example2 c = S.concat $ L.toChunks $ encode c


------------------------------------------------------------------------------
data Coord = Coord …