[erlang-questions] if vs. case (long)

Jay Nelson jay@REDACTED
Thu Mar 13 14:13:45 CET 2008

On Mar 13, 2008, at 1:12 AM, Mats Cronqvist wrote:

> Ulf Wiger wrote:
>> A colleague of mine would most definitely write this as
>>   DebugOn andalso log(Var).

That's definitely shorter, although Mats points out the returning a  
boolean issue.  Not a bad solution and most telling of its intent,  
including any side-effects caused by log/1.

>  that's too verbose, and log/1 has to return a boolean. here's the  
> Right Way(tm);
> [log(Var) || DebugOn].
>  mats
> p.s. sarcasm! this construct is only to be used in obfuscated  
> erlang competitions!

I tend to forget about the ways to abuse list comprehensions.  I  
don't mind adopting a particular idiomatic odd construct usage if it  
has the following characteristics:

1) It is used to mean precisely one thing
2) You are consistent in your usage
3) Once figured out, it cannot be confused with normal usage of the  
4) Optional: put it in a macro and give it a better name

Since andalso is good enough and clear I would use it or put it in a  
macro, although to me it has a PERL feel to it rather than an erlang  
feel.  I tend to expect erlang code to execute everything, rather  
than to skip over some statements.  I don't expect this in guard or  
case situations where andalso is normally used.

But there may be another good (ab)use of list comprehensions that I  
haven't tried yet ;-).  And in the list comprehension case, the  
statement _is_ executed.  You expect some elements of the source list  
to be skipped, possibly all of them.

The comprehension also can be expanded to a series of things:

[log(A) and log(B) || DebugOn]

How's this for obfuscation?

[[log(E) || E <- LogVars] || DebugOn]


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