Pop3 connection with D

[Andrei Alexandrescu (See Website For Email)]

kris wrote:
> Andrei Alexandrescu (See Website For Email) wrote:
>> kris wrote:
>>
>>> Andrei Alexandrescu (See Website For Email) wrote:
>>>
>>>> kris wrote:
>>>>
>>>>> Andrei Alexandrescu (See Website For Email) wrote:
>>>>>
>>>>>> Possibly implementing protocols could be an area in which DSLs 
>>>>>> might help, e.g. in the guise of automata and of course regex. I 
>>>>>> once designed a little DSL for implementing FTP and it was of 
>>>>>> great help.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> Compile-time DSLs?
>>>>
>>>>
>>>>
>>>> Obviously.
>>>
>>>
>>> That sounds reasonably sophisticated.
>>>
>>> Just out of interest, how does one easily debug something like that?
>>
>>
>> Very easy. The FTP protocol is described as a collection of states 
>> with prescribed transitions in between them. A DFA (in C++) 
>> implemented them in a compact manner; whenever the DFA would bail out 
>> (by throwing), it would tell what state it was in, what was the 
>> expected input, and what the actual input was. I remember that library 
>> was a rewrite of a library written in a "old school" style from first 
>> principles (e.g. int and if and switch), meaning that following what 
>> the code does and where you are was horrendous. We were very pleased 
>> with the rewrite.
>>
>>
>> Andrei
> 
> sounds good.
> 
> Yet, you appear to be describing a "black-box" of sorts, with diagnostic 
> exceptions? My guess is that interactive "step through" debugging, with 
> something like MSVC6 for example, would not be particularly feasible?

Stepping through was of course possible and useful. The main difference 
was that stepping through manually-written code was replaced by stepping 
through the more compact templated code. The instantiation types are 
different and therefore different actual binary code maps to the same 
source line.

Andrei