anchor.diff:  
                       type StructuralEquatable<'a when 'a : struct and 'a :> IStructuralEquatable>() =
                           member __.Equals (ec:IEqualityComparer, x:'a, y:'a) = Calls.StructuralEqualityEquals (ec, x, y)
  +                        member __.GetHashCode (ec:IEqualityComparer, x:'a) = Calls.StructuralEqualityGetHashCode<'a> (ec, x)
   
                       type Equatable<'a when 'a : struct and 'a :> IEquatable<'a>>() =
                           member __.Equals (_:IEqualityComparer, x:'a, y:'a) = Calls.EquatableEquals (x, y)
   
                       type Equality<'a when 'a : struct and 'a : equality>() =
                           member __.Equals (_:IEqualityComparer, x:'a, y:'a) = x.Equals y
  +                        member __.GetHashCode (_:IEqualityComparer, x:'a) = x.GetHashCode ()
   
                   module RefType = 
                       type StructuralComparable<'a when 'a : not struct and 'a : null and 'a :> IStructuralComparable>() =
  
positive.code:             // functionality of GenericSpecializedHash should match GenericHashParamObj, or return null
              // for fallback to that funciton. 
              module GenericSpecializeHash =
                  let standardTypes (t:Type) : obj =
                      if   t.Equals typeof<bool>       then box (Func<IEqualityComparer,bool      ,int>(fun _ a -> a.GetHashCode()))
                      elif t.Equals typeof<float>      then box (Func<IEqualityComparer,float     ,int>(fun _ a -> a.GetHashCode()))
  
negative.code:                             | null, null -> true
                              | null, _ | _, null -> false
                              | _, _ -> x.Equals y
  
                          member __.GetHashCode (_:IEqualityComparer, x:'a) =
                              match x with
                              | null -> 0
                              | _ -> x.GetHashCode ()
  
                  module DummyTypes =
                      let doNotEat () = raise (Exception "not for eating! these types only exist for getting typedef.")
  