[erlang-questions] Re: Defensive Programming

[Henning Diedrich]

Thanks Steve,

that question of "is it recoverable?" makes a lot of sense to clarify. I 
am taking note.

In my case I am writing a lib function for others to use, which is 
exactly why I would like to give them more information on the error.

Even though they might not be able to recover it, they should at least 
know why it didn't work, instead of just getting a bad match for "ok = "

I meanwhile conclude that the trimmest variant will be to care less and 
demand that the user of the function test for the return value directly 
handed over from the gen_tcp:send() call. Making it

login(Name, Password) ->

       ...
        gen_tcp:send(Socket, term_to_binary(Str)).



That looks the Erlangest an hands responsibility to the person who can 
actually answer the 'recoverability question', the user of the lib.

I realize I'd like to take away chances of frustration, puffing it up in 
the process.

Thanks for taking a look!
Henning



Steve Davis wrote:
> Hi Henning,
>
> This isn't intended to be any kind of definite answer, and I'm
> interested to see how others respond.
>
> In my case how I deal with this question is that I'd probably ask
> myself:
>
> *Is this exceptional case _recoverable_,? e.g. in the case of the tcp
> send, you could try to resend the data, so the first idiom may do it.
>
> If it's not recoverable, I'd just let it crash out. In fact I would
> likely force it to crash out using the second idiom.
>
> If I want to get fancy with error handling, I find that try..catch at
> the top level is usually enough.
>
> A further aside to this is that a certain Mr Armstrong once introduced
> me to an interesting "transactional" idiom also, namely:
>
> try begin
> ...
> end catch
> ...
>
> Regards,
>
> /s
>
> On May 16, 5:04 pm, Henning Diedrich <hd2...@REDACTED> wrote:
>   
>> Hi list,
>>
>> I have a question about the Erlang way.
>>
>> I realize I keep programming defensive using exceptions/error calls to
>> *label failure* more precisely.
>>
>> E.g. ( - PRESUMABLY WRONG - )
>>
>> login(Name, Password) ->
>>
>>        ...
>>         case
>>                 gen_tcp:send(Socket, term_to_binary(Str)) of
>>                      ok -> ok;
>>                      _ -> erlang:error(*sending_failed, {Str }*)
>>        end
>>        ...
>>
>> Instead of simply
>>
>> login(Name, Password) ->
>>
>>        ...
>>         ok = gen_tcp:send(Socket, term_to_binary(Str)),
>>        ...
>>
>> It feels wrong in Erlang and I wonder if I am missing out on something.
>>
>> If somebody has a pointer to read up on this, thanks in advance,
>>
>> Henning
>>
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