anchor.diff:                      Column = None
                   }
           }
  +
       member this.FunctionInvocation(source : SourceInfo, func : FunctionInvocationExpr) =
           match scope.Model.Builtin.Functions.TryFind(func.FunctionName) with
           | None -> failAt source <| sprintf "No such function: ``%O``" func.FunctionName
  
positive.code:                     if not allowNotFound then failAt objectName.Source r
                      else Missing
          }
      member this.ColumnName(source : SourceInfo, columnName : ColumnName) =
          let tblAlias, tblInfo, name = scope.ResolveColumnReference(columnName) |> foundAt source
          {   Expr.Source = source
  
negative.code:         | CaseExpr case -> this.Case(source, case)
          | ScalarSubqueryExpr select -> this.ScalarSubquery(source, select)
          | RaiseExpr raise -> { Source = source; Value = RaiseExpr raise; Info = ExprInfo<_>.OfType(InferredType.Any) }
  
      member this.Expr(expr : Expr, ty : CoreColumnType) =
          let expr = this.Expr(expr)
          cxt.Unify(expr.Info.Type, ty) |> resultOk expr.Source
  