3

我已经到了论文的第 3 部分。Haskell XML 工具箱的食谱，其中包含 M. Ohlendorf 的RDF 文档处理示例。

这是我写的程序，

import Text.XML.HXT.Core
import System.Exit
import System.Environment
import Data.Maybe

main = do
  args       <- getArgs
  (al, src)  <- cmdLineOpts args
  [rc]       <- runX (processDocument al src)
  exitWith ( if rc >= c_err
             then ExitFailure (-1)
             else ExitSuccess
           )

cmdLineOpts :: [String] -> IO (Attributes, String)
cmdLineOpts []  = return ([("","")], "")
cmdLineOpts xss = return (zip [""] xss :: Attributes, last xss)

processDocument :: Attributes -> String -> IOSArrow b Int
processDocument al src =
    readDocument al src -- lecture du document en appliquant les attributes                                                                                            
    >>>
    removeAllWhiteSpace >>> propagateNamespaces
    >>>
    writeDocument al (fromMaybe "" (lookup a_output_file al))
    >>>
    getErrStatus

但我仍然遇到以下错误

hxtuto.hs:28:17:
    Couldn't match expected type `XIOSysState -> XIOSysState'
           against inferred type `(String, String)'
      Expected type: SysConfigList
      Inferred type: Attributes
    In the first argument of `readDocument', namely `al'
    In the first argument of `(>>>)', namely `readDocument al src'
Failed, modules loaded: none.

看来这是我的实现cmdLineOpts不太合适。

这里有什么问题 ？我该如何解决？

谢谢你的帮助 ！

4

1 回答 1

1

由于 readDocument 和 writeDocument 的第一个参数是 [SysConfig]，您可能希望使用 GetOpt 之类的包来处理从命令行读取文本并将其转换为所需对象的内务管理。我从论文的第 50 页获取了“可用选项”列表，并使用当前对应的 SysConfigs（来自 Text.XML.HXT.Arrow.XmlState.SystemConfig）创建了一个 Options 类型。除了为手头的特定应用程序定制的部分外，其余部分（例如 cmdLineOpts）直接取自 GetOpt 文档。

import System.Console.GetOpt
import System.Environment
import System.Exit 
import Text.XML.HXT.Core

data Options = Options {
    withvalidate :: SysConfig
  , withchecknamespaces :: SysConfig
  , withcanonicalize :: SysConfig
  , withremovews :: SysConfig
  , withtrace :: SysConfig
  , output_file :: String } 

defaultOptions = Options { withvalidate = (withValidate no)
                         , withchecknamespaces = (withCheckNamespaces no)
                         , withcanonicalize = (withCanonicalize no)
                         , withremovews = (withRemoveWS no)
                         , withtrace = (withTrace 0)
                         , output_file = "" } 

options :: [OptDescr (Options -> Options)]
options =
 [ Option ['V'] ["withValidate"] 
   (ReqArg (\v opts -> opts { withvalidate = withValidate (v == "yes") } ) "") 
   "perform DTD validation"
 , Option ['n'] ["withCheckNamespaces"] 
   (ReqArg (\n opts -> opts { withchecknamespaces = withCheckNamespaces (n == "yes") } ) "")
   "check namespaces"
 , Option ['c'] ["withCanonicalize"] 
   (ReqArg (\c opts -> opts { withcanonicalize = withCanonicalize (c == "yes") } ) "")
   "canonicalize document"
 , Option ['w'] ["withRemoveWS"] 
   (ReqArg (\w opts -> opts { withremovews = withRemoveWS (w == "yes") } ) "")
   "remove whitespace used for document indentation"
 , Option ['t'] ["withTrace"] 
   (ReqArg (\t opts -> opts { withtrace = withTrace (read t) } ) "")
   "set trace level" 
 , Option ['o'] ["outputFile"] 
   (ReqArg (\o opts -> opts { output_file = o } ) "") 
   "output file" ]

cmdLineOpts :: [String] -> IO (Options, [String])
cmdLineOpts argv =
    case getOpt Permute options argv of
      (o, n, []) -> return (foldl (flip id) defaultOptions o, n)
      (_, _, errs) -> ioError (userError (concat errs ++ usageInfo header options))
    where header = "Using: [OPTION ...]"

main :: IO ()
main = do (opts, (src:_)) <- cmdLineOpts =<< getArgs 
          [rc] <- runX $ processDocument opts src
          exitWith $ if rc >= c_err then ExitFailure (-1) else ExitSuccess

processDocument :: Options -> String -> IOSArrow b Int
processDocument (Options val ns can ws tr out) src =
    readDocument [val, ns, can, ws, tr] src >>> 
    removeAllWhiteSpace >>> propagateNamespaces >>>
    writeDocument [val, ns, can, ws, tr] out >>>
    getErrStatus
于 2012-03-19T00:02:25.930 回答