F＃从词法分析器中捕获异常

Question

我试图让我的F＃代码从词法分析器中捕获错误输入的异常。虽然引发了异常，但它没有被其他模块捕获。有人能帮忙吗？

let lexstring expr =
    try
        LexBuffer<char>.FromString(expr)
    with 
     Lexer.IllegalCharacter  -> failwith "XXXXXXXXXXXX" 

词法分析器代码如下：

| ['-']?digit+('.'digit+)?(['e''E']digit+)?     { FLOAT (Double.Parse(lexeme lexbuf)) }
// EOF
| eof   { EOF }
| _     { raise IllegalCharacter }

错误消息如下：

Lexer.IllegalCharacter occurred
  HResult=-2146233088
  Message=Exception of type 'Lexer+IllegalCharacter' was thrown.
  Source=FSharp.Core
  StackTrace:
       at Microsoft.FSharp.Core.Operators.Raise[T](Exception exn)
       at Lexer._fslex_tokenize(Int32 _fslex_state, LexBuffer`1 lexbuf) in E:\Programming\F#\fsapp_ozan\parser\Lexer.fsl:line 48
  InnerException: