错误没有被捕获

Question

我写了一个上传xml文件的脚本，看下面的代码片段：

open System.Xml
open System.IO
open System

type XmlErrorLoad = 
    | Success of XmlDocument
    | FileNotFound of FileNotFoundException
    | OtherException of Exception

let doc (filename:string) = 
    try
        let file = XmlDocument()
        file.Load(filename)
        Success file
    with
    | :? FileNotFoundException as ex -> FileNotFound ex 
    | :? Exception as ex -> OtherException ex


let fileNotExists = doc("C:\Temp\ip2.xml")
match fileNotExists with
| Success s -> ()
| FileNotFound ex -> printfn "File not found: %s" ex.Message
| OtherException ex -> printfn "Exception: %s" ex.Message

在这种情况下，ip2.xml 文件不存在，它应该抛出错误 FileNotFound 并在屏幕上打印。

"File not found: %s" ex.Message

但我收到消息

val fileNotExists : XmlErrorLoad =
  FileNotFound
    System.IO.FileNotFoundException: Could not find file 'C:\Temp\ip2.xml'.
File name: 'C:\Temp\ip2.xml'
   at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
   at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
   at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize)
   at System.Xml.XmlDownloadManager.GetStream(Uri uri, ICredentials credentials, IWebProxy proxy, RequestCachePolicy cachePolicy)
   at System.Xml.XmlUrlResolver.GetEntity(Uri absoluteUri, String role, Type ofObjectToReturn)
   at System.Xml.XmlTextReaderImpl.OpenUrlDelegate(Object xmlResolver)
   at System.Threading.CompressedStack.runTryCode(Object userData)
   at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
   at System.Threading.CompressedStack.Run(CompressedStack compressedStack, ContextCallback callback, Object state)
   at System.Xml.XmlTextReaderImpl.OpenUrl()
   at System.Xml.XmlTextReaderImpl.Read()
   at System.Xml.XmlLoader.Load(XmlDocument doc, XmlReader reader, Boolean preserveWhitespace)
   at System.Xml.XmlDocument.Load(XmlReader reader)
   at System.Xml.XmlDocument.Load(String filename)
   at FSI_0004.doc(String filename) in D:\f#\samples\ip.fsx:line 20

Answer 1

我已经尝试将您的代码作为 F# Interactive 的输入并获得了所需的消息

File not found: Could not find file 'C:\Temp\ip2.xml'.

除了输出 F# Interactive 列出了代码中定义的所有值，所以我还打印了以下内容：

type XmlErrorLoad =
  | Success of XmlDocument
  | FileNotFound of FileNotFoundException
  | OtherException of Exception
val doc : filename:string -> XmlErrorLoad
val fileNotExists : XmlErrorLoad =
  FileNotFound
    System.IO.FileNotFoundException: Could not find file 'C:\Temp\ip2.xml'.
File name: 'C:\Temp\ip2.xml'
   at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
   at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
   at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize)
   at System.Xml.XmlDownloadManager.GetStream(Uri uri, ICredentials credentials, IWebProxy proxy, RequestCachePolicy cachePolicy)
   at System.Xml.XmlUrlResolver.GetEntity(Uri absoluteUri, String role, Type ofObjectToReturn)
   at System.Xml.XmlTextReaderImpl.OpenUrlDelegate(Object xmlResolver)
   at System.Threading.CompressedStack.runTryCode(Object userData)
   at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
   at System.Threading.CompressedStack.Run(CompressedStack compressedStack, ContextCallback callback, Object state)
   at System.Xml.XmlTextReaderImpl.OpenUrl()
   at System.Xml.XmlTextReaderImpl.Read()
   at System.Xml.XmlLoader.Load(XmlDocument doc, XmlReader reader, Boolean preserveWhitespace)
   at System.Xml.XmlDocument.Load(XmlReader reader)
   at System.Xml.XmlDocument.Load(String filename)
   at FSI_0003.doc(String filename)
val it : unit = ()

作为 REPL 反馈的一部分，您只能在 F# Interactive 中获得此输出。在普通程序中不会产生此输出。

错误没有被捕获

Error does not get caught

f#

exception