optimization of list comprehensions

Serge Aleynikov <>
Thu Mar 2 14:36:44 CET 2006


I do want to throw a vote for Mats' suggestion on the alternative syntax:

(I || I <- List) -> ok

What I also find limiting is that it's not possible to have an 
accumulator when using list comprehension.  Perhaps something like this 
could also be considered (unless someone can suggest a better syntax):

[Acc+1, I || Acc, I <- List](0) -> Acc1
                              ^
                              |
                        Initial Acc's value
Serge

Robert Virding wrote:
> I have been thinking about this a bit and I wonder if the constructing 
> of the return list really causes any problems. Space-wise it will only 
> be as large as the size of the input list, so I wouldn't worry.
> 
> Robert
> 
> Ulf Wiger (AL/EAB) skrev:
> 
>> I've seen many examples of how people use
>> list comprehensions as a form of beautified
>> lists:foreach() - that is, they don't care
>> about the return value of the comprehension.
>>
>> I hesitate to say that it's bad practice,
>> even though one will build a potentially
>> large list unnecessarily, since it's actually looks a lot nicer than 
>> using lists:foreach().
>>
>> Question: would it be in some way hideous
>> to introduce an optimization where such
>> list comprehensions do everything except
>> actually build the list? Then they could
>> execute in constant space.
>>
>> /Ulf W
>>
> 




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