Dispatching on a variant

[language_fan]

Sat, 26 Sep 2009 18:51:19 -0400, #ponce thusly wrote:

>> Exactly, this is what I mentioned previously. Isn't it ugly compared to
>> 
>>   type Event = Mouse | Key | Move;
>> 
>>   void dispatchEvent(Event event) {
>>     match(event) {
>>       Mouse m => m.squeek();
>>       Key k => ...
>>       ...
>>     }
>>   }
>> 
>> What's with all the language proposals here? Why hasn't anyone proposed
>> this before? This is in fact very helpful - that's why several modern
>> languages have adopted it.
> 
> Algebraic data types are indeed a neat feature. But the languages which
> implemented this (ML, Haskell, scala...) seems only to be functionals
> one. I suppose it's because it replaces enums and unions for those. In
> procedural languages one can emulate this with 1 enum + 1 union.
> 
> I would prefer having some computed goto (through final switch).

Agreed.

On the other hand I cannot fully agree that Scala is more a functional 
language than something else. The core is both object oriented and 
functional. It is even more object oriented (purer) than most mainstream 
C-like languages. By this I mean that in my opinion it is not impossible 
to imagine that D also implemented something like case classes and 
extended switch to handle also simple patterns.