[erlang-questions] behavior of lists:append/1

[Michał Muskała]

My understanding is that for most functions in the Erlang standard library, if you don't uphold the contract the documentation specifies the function can crash, but it could also return whatever - in short "garbage in, garbage out" applies.

Michał.
On 15 Sep 2019, 18:45 +0100, Karlo Kuna <kuna.prime@REDACTED>, wrote:
> Hello,
>
> i have found surprising  behavior of function lists:append/1:
>
> spec and documentation  are in a agreement that this function should accept lists of lists ( [List] ) ,
> and return list of T ( [T] ), however when we use function like:
>
>      lists:append([a]) %wrong input parameter
> one gets:
>      a  % wrong type of a return
>
> implementation assumes correct type:
>
> append([E]) -> E; % E is not checked for type
> append([H|T]) -> H ++ append(T);
> append([]) -> [].
>
> simple solution could be:
>
> lists:append([E]) when is_list(E) -> E
>
> am i missing something?
>
> _______________________________________________
> erlang-questions mailing list
> erlang-questions@REDACTED
> http://erlang.org/mailman/listinfo/erlang-questions
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://erlang.org/pipermail/erlang-questions/attachments/20190915/792efd23/attachment.htm>