anchor.diff:              using (collection.GetEnumerator()) 
                   (fun it -> whileLoop (fun () -> it.MoveNext()) (fun () -> it.Current |> func))
           
  +        [<DebuggerStepThrough>]
           member inline this.Using(disposable : #System.IDisposable, body) = 
               let body' = fun () -> body disposable
               this.TryFinally(body', (fun () -> disposable.Dispose()))
  
positive.code: open System.Collections.Concurrent
  open System.Collections.Generic
  open System.ComponentModel.Composition
  open System.IO
  open System.Linq
  open System.Threading
  
negative.code:     [<Sealed>]
      type ErrorHandlingBuilder() = 
          
          [<DebuggerStepThrough>]
          member inline __.Bind(v, f) = 
              match v with
              | Choice1Of2(x) -> f x
              | Choice2Of2(s) -> Choice2Of2(s)
          
          [<DebuggerStepThrough>]
          member inline __.ReturnFrom v = v
          
          [<DebuggerStepThrough>]
          member inline __.Return v = Choice1Of2(v)
          
          [<DebuggerStepThrough>]
          member inline __.Zero() = Choice1Of2()
          
          [<DebuggerStepThrough>]
          member inline __.Combine(a, b) = 
              match a, b with
              | Choice1Of2 a', Choice1Of2 b' -> Choice1Of2 b'
  