[erlang-questions] Doubt with lists:dropwhile

[Jesse Gumm]

This is a misinterpretation of lists:dropwhile.

lists:dropwhile will remove elements of a list starting with the first
and iterate through the list, continuing to drop elements as long as
the predicate returns true.  However, as soon as the predicate returns
false, it'll just stop and return.

So in your case, the dropwhile didn't match the first element, so it
just returned.

Easy Example:

> LessThan5 = fun(X) X < 5 end.

> lists:dropwhile(LessThan5,[1,2,3,4,5,6]).
[5,6]

>lists:dropwhile(LessThan5,[6,5,4,3,2,1]).
[6,5,4,3,2,1]

-Jesse

On Wed, Apr 25, 2012 at 12:34 PM, Farruco Sanjurjo <madtrick@REDACTED> wrote:
> Hi,
>
> I'm not getting the expected result while using lists:dropwhile/2
>
> Here is an example of my problem:
>
> Data = <<"HTTP/1.1 205 Reset Content\r\n
>               Header-A: A\r\n
>               Header-C : dGhlIHNhbXBsZSBub25jZQ==\r\n
>               Header-D: D\r\n\r\n
>               ">>,
>
> lists:dropwhile(fun(E) -> E == <<>> end, binary:split(Data, <<"\r\n">>,
> [trim, global])).
>
> And this is the result:
>
> [<<"HTTP/1.1 205 Reset Content">>,
>  <<"\n              Header-A: A">>,
>  <<"\n              Header-C dGhlIHNhbXBsZSBub25jZQ==">>,
>  <<"\n              Header-D: D">>,<<>>,
>  <<"\n              ">>]
>
> But on the result above, there's a <<>> which if I understand the manpage of
> lists:dropwhile shouldn't be there.
>
> Am I misunderstanding something?
>
>
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-- 
Jesse Gumm
Owner, Sigma Star Systems
414.940.4866 || sigma-star.com || @jessegumm