anchor.diff:      %% iterate from the right so we can append to the head of lists
       {ResultTypeSet, Q2} = lists:foldl(CompileColFn, Acc, Sel),
   
  -    {ColTypes, Errors} = lists:mapfoldl(
  +    {ColTypes, Errors} = my_mapfoldl(
           fun(ColASTX, Errors) ->
               infer_col_type(DDL, ColASTX, Errors)
           end, [], Sel),
  
positive.code: prepend_select_columns(V, Acc) ->
      [V | Acc].
  
  %%
  compile_select_clause(DDL, ?SQL_SELECT{'SELECT' = #riak_sel_clause_v1{ clause = Sel } } = Q) ->
      CompileColFn = 
  
negative.code: 
  %%
  -spec infer_col_type(#ddl_v1{}, selection(), Errors1::[any()]) ->
          {Type::simple_field_type() | error, Errors2::[any()]}.
  infer_col_type(_, {Type, _}, Errors) when Type == sint64; Type == varchar;
                                            Type == boolean; Type == double ->
      {Type, Errors};
  