T = lists:foldl(fun(L2, A2) ->
% do my logic on each item in the list here,
% the line below appends the result of all the
% work we do here to the accumulator A2.
end, , R),
The key to the above is the 'A2' accumulator which stores the result of each loop in a list.
This is useful when you need to take a list work on it to create a new list. Especially when working with libraries like mochiweb, webmachine where the output might be in json.
You could use the structure above to generate a mochijson2 friendly list from a regular erlang list.
[lists:foldl/3 man page][http://www.erlang.org/doc/man/lists.html#foldl-3]