anchor.diff:  
       /// Looks the underlying tag id for given union case name using linear search.
       member _.GetTag (caseName : string) : int =
  -        let caseNames = caseNames
  +        let caseNames = caseNames.Value
           let n = caseNames.Length
           let mutable i = 0
           let mutable notFound = true
  
positive.code:     member _.IsAnonymousRecord = isAnonymousRecord
  
      /// F# record field shapes
      member _.Fields = recordFields
  
      /// Creates an uninitialized instance for given record
      [<MethodImpl(MethodImplOptions.AggressiveInlining)>]
  
negative.code:         member _.IsStructRecord = typeof<'Record>.IsValueType
          member _.IsAnonymousRecord = isAnonymousRecord
  
          member _.Fields = recordFields.Value |> Array.map unbox
          member s.Accept v = v.Visit s
  
  and IFSharpRecordVisitor<'R> =
  