anchor.diff:                      Column = None
                   }
           }
  +
       member this.Cast(source : SourceInfo, cast : CastExpr) =
           let input = this.Expr(cast.Expression)
           let ty = InferredType.OfTypeName(cast.AsType, input.Info.Type)
  
positive.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
  
negative.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
  