Erlang: List Comprehension to an Existing List

I am trying to create a new list via a list comprehension but want those new values to be included in an existing list.

More specifically, I am try to create a string out of the date and will have some string formatting between the values ( a dash - ). The existing list will be a template if you will with the dash.

Here is what I have so far:

{Date, Time} = erlang:universaltime().
DateList = tuple_to_list(Date).
DateListString = [ integer_to_list(X) || X < DateList ].
DateListStringConcatenate = lists:flatten(DateListString).

The result s开发者_运维百科hould be something along "20101121"

But, what I want is "2010-11-21"

So I am thinking about the DateListString comprehension "comprehending" to an existing list with "-" after the first and second element.

Any suggestions accompanied with concrete code samples much appreciated.

1> {{Y,M,D},_} = erlang:universaltime().
{{2010,11,21},{16,42,56}}
2> lists:flatten(io_lib:format("~p-~p-~p", [Y,M,D])).
"2010-11-21"

If you really want it in a list comprehension then you could do the following:

{Date, Time} = erlang:universaltime().
DateList = tuple_to_list(Date).
DateListString = [ [$- | integer_to_list(X)] || X <- DateList ].
[_ | DateListStringConcatenate] = lists:flatten(DateListString).

Roberto's is a better/more efficient solution to this but in case you wondered how you might do it with a list comprehension this would be one way.

This is a possible solution, but I feel that it is not an elegant one. Also, it does not use list comprehension.

1> {Date, Time} = erlang:universaltime().
{{2010,11,21},{14,51,23}}
2> DateList = tuple_to_list(Date).
[2010,11,21]
3> DateListString = lists:zipwith(fun(X,Y) -> integer_to_list(X) ++ Y end, DateList, ["-","-",""]).           
["2010-","11-","21"]
4> DateListStringConcatenate = lists:flatten(DateListString).
"2010-11-21"