anchor.diff:              let extraColorInfo =
                   maybe { let! document = Option.ofNull document
                           let! parsedDocument = Option.ofNull document.ParsedDocument
  -                        let! pc = tryCast<ParseAndCheckResults> document.ParsedDocument.Ast
  +                        let! pc = Option.tryCast<ParseAndCheckResults> document.ParsedDocument.Ast
                           return! pc.GetExtraColorizations() }
   
               match (this.Document, line, offset, length, style) with
  
positive.code:                     let localParsedDocument = document.ParsedDocument
                      if localParsedDocument <> null then
                          localParsedDocument.Ast 
                          |> tryCast<ParseAndCheckResults>
                          |> Option.iter (getAndProcessSymbols >> Async.Start))
  
      let makeChunk (lineNumber: int) (style: ColorScheme) (offset:int) (extraColorInfo: (Range.range * TokenColorKind)[] option) (token: TokenInformation) =
  
negative.code: open Microsoft.FSharp.Compiler
  open Microsoft.FSharp.Compiler.SourceCodeServices
  open FSharp.CompilerBinding
  open ExtCore.Control
  
  module FSharpSyntaxModeInternals =
      let contains predicate sequence =
  