[erlang-questions] Erlang vs Clojure

Kostis Sagonas <>
Sun Nov 25 00:29:02 CET 2007


Ciprian Dorin Craciun wrote:
> 
>    It's not only about something you can or can not. It's also about
> aesthetics.

Yes.  I very much agree on this.  The only problem is that different 
people have different aesthetics.

(Btw, I am not the one who designed the macro system and I am far from 
enamoured by it, so I am not certain why I am currently defending it. 
But here is a response to your mail in any case.)

>    Compare the following two forms:
>    ?if_(guard, {do something})
>    vs
>    if_ guard -> {do something} end
> 
>    Which one looks more natural?

Well, in Erlang, I would say it's definitely the first that looks more 
natural for the following two reasons:

  1. It looks like a function call, and function calls are very natural
     in a functional language.

  2. Erlang's if construct has totally different semantics than the ones
     you want there; it fails if the guard does not evaluate to true.

>    What if I want to execute two operations?
>    ?if_(guard, begin {operation-1}, {operation-2} end)
>    vs
>    if_ guard -> {operation-1}, {operation-2} end

You are making a good argument, but I'd say the best thing to do is to 
factor the two operations out in a function in such a case. (Actually, 
the only reason why you need the begin+end is that the ',' symbol is 
overloaded in Erlang).

>    What if I decide there is an else case? In my this case it's a
> matter of removing a character '_' and adding the true case. In your
> case I would have to rewrite a good portion.

Well, not really.  Your case would be something like:

   if guard -> {do something}; true -> {do something else} end

and in my case it would be a macro:

   ?if_else(guard, {do something}, {do something else}).

(and writing the new macro -- the ?if_ macro would be a special case 
where the true part is just the above macro with the else part 'ok')

>    The idea behind a good macro is to be able to "blend" inside the
> "built-in" syntax and not stand out.

I can give you many reasons why macros in Erlang suck but the "macros 
stand out in the language" argument comes pretty low on that list. I am 
not so convinced that Lisp-like macros is what Erlang desperately needs.
But then again, disagreements such as these are exactly the reason we 
have so many different and diverse programming languages...

Cheers,
Kostis



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