anchor.diff:  
   let TextSpans = R.textSpans
   let SaveTextSpans() = R.saveTextSpans <- true
  +
  +let baseCtor thisExpr (t: Concrete<TypeDefinition>) c a =
  +    if t.Entity = Definitions.Obj then thisExpr
  +    elif (let fn = t.Entity.Value.FullName in fn = "WebSharper.ExceptionProxy" || fn = "System.Exception") then 
  +        match a with
  +        | [] -> Undefined
  +        | [msg] -> ItemSet(thisExpr, Value (String "message"), msg)
  +        | [msg; inner] -> 
  +            Sequential [
  +                ItemSet(thisExpr, Value (String "message"), msg)
  +                ItemSet(thisExpr, Value (String "inner"), inner)
  +            ]
  +        | _ -> failwith "Too many arguments for Error"
  +    else
  +        BaseCtor(thisExpr, t, c, a) 
   
   let private transformClass (rcomp: CSharpCompilation) (sr: R.SymbolReader) (comp: Compilation) (annot: A.TypeAnnotation) (cls: INamedTypeSymbol) =
       let isStruct = cls.TypeKind = TypeKind.Struct
  
positive.code:                                 match c.Initializer with
                                  | Some (CodeReader.BaseInitializer (bTyp, bCtor, args, reorder)) ->
                                      CombineStatements [
                                          ExprStatement (BaseCtor(This, bTyp, bCtor, args) |> reorder)
                                          c.Body
                                      ]
                                  | Some (CodeReader.ThisInitializer (bCtor, args, reorder)) ->
                                      CombineStatements [
                                          ExprStatement (BaseCtor(This, NonGeneric def, bCtor, args) |> reorder)
                                          c.Body
                                      ]
                                  | None -> c.Body
  
negative.code:                                 | { Entity = td } when td = Definitions.Obj || td = Definitions.ValueType ->
                                      Empty
                                  | b ->
                                      ExprStatement (baseCtor This b (ConstructorInfo.Default()) [])
                              let init =
                                  if hasInit then 
                                      ExprStatement <| Call(Some This, NonGeneric def, NonGeneric initDef, [])
  