F# decompiled pattern matching

Sample01.cs

// Decompiled with JetBrains decompiler
// Type: FSharpParts.FSharpParts
// Assembly: FSharpParts, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null
// MVID: 54894392-FF35-398D-A745-038392438954
// Assembly location: D:\temp\SharpExperiments\FSharpParts\bin\Debug\FSharpParts.dll

using CSharpParts;
using Microsoft.FSharp.Core;

namespace FSharpParts
{
  [CompilationMapping(SourceConstructFlags.Module)]
  public static class FSharpParts
  {
    public static string selector(object obj)
    {
      object obj1 = obj;
      if (obj1 is ClassA)
        return "A";
      if (obj1 is ClassB)
        return "B";
      if (obj1 is ClassC)
        return "C";
      if (obj1 is ClassD)
        return "D";
      return obj1 is ClassE ? "E" : "?";
    }
  }
}

Sample01.fs

namespace FSharpParts

open CSharpParts

module FSharpParts =

    let selector (obj: obj) =
        match obj with
        | :? ClassA -> "A"
        | :? ClassB -> "B"
        | :? ClassC -> "C"
        | :? ClassD -> "D"
        | :? ClassE -> "E"
        | _ -> "?"