anchor.diff:          ///         to make sure.
           ///     </para>
           /// </summary>
  -        | NoSuchView of name : string
  +        | NoSuchView of func : DFunc
           /// <summary>
           ///     A view lookup failed during downclosure checking.
           ///
  
positive.code:       : Result<IteratedDFunc * BoolExpr<Sym<Var>>, Error> =
          (* To do the base downclosure, we need to replace all instances of the
             iterator in the definition with 0. *)
          let subZero v = if v = iterator then AInt 0L else AVar (Reg v)
  
          let baseDefn = downclosureMap subZero defn
  
          (* Base downclosure for a view V[n](x):
               D(emp) => D(V[0](x))
  
negative.code:         | MixedFuncType view ->
              fmt "constraint '{0}' mixes iterated and non-iterated views"
                  [ printDView view ]
          | NoSuchView name
              -> fmt "no view prototype for '{0}'" [ printDFunc name ]
          | LookupError(func, err) ->
              wrapped "lookup for view"
                  (printDFunc func)
                  (err |> Core.Instantiate.Pretty.printError)
          | IteratorOnNonIterated func ->
              fmt "view '{0}' is not iterated, but used in an iterated constraint"
                  [ printIteratedContainer
  