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From: Arved Sandstrom <asandstrom2@eastlink.ca>
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Subject: Re: Java 8 Streams and Eratosthenes
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On 06/05/2013 04:44 AM, Sebastian wrote:
> Am 05.06.2013 09:03, schrieb Sebastian:
>> Am 05.06.2013 00:35, schrieb Arved Sandstrom:
>>> On 06/04/2013 06:54 PM, Sebastian wrote:
>>>> Hello there,
>>>>
>>>> I'd like to start an open discussion on issues involving the Streams
>>>> API. As an exercise, I have looked at generating the first n primes,
>>>> for some given n, using the sieve of Eratosthenes. It seemed a
>>>> plausible enough proposition, seeing that the sieve involves repeatedly
>>>> filtering a sequence of integers.
>>>>
>> [snip]
>>>>
>>>> Perhaps the lesson is that some things are best not done using
>>>> streams.
>> [snip]
>>>>
>>>> What are your opinions?
>>>>
>>>> Best,
>>>> Sebastian
>>> [ SNIP ]
>>>
>>> Some things are best not done using Java. Given interop, I'd use Closure
>>> or Scala for this type of stuff, if the main program is still Java.
>>>
>>> AHS
>>
>> That's a bit of a dodge, isn't it? Scala may be a nice language, but
>> that doesn't help with investigating Java's strength and weaknesses.
>>
>> -- Sebastian
>
> Or perhaps it does. There are many Scala implementations of this
> algorithm on the internet, cf. this one
>
>   def primes : Stream[Int] = {
>
>     var is = Stream from 2
>
>     def sieve(numbers: Stream[Int]): Stream[Int] = {
>       Stream.cons(
>         numbers.head,
>         sieve(for (x <- numbers.tail if x % numbers.head > 0) yield x))
>     }
>
>     sieve(is)
>    }
>
> from
> http://louisbotterill.blogspot.de/2009/07/scala-lazy-evaluation-and-sieve-of.html
>
>
> What the implementations all seem to have in common is the ability to
> access the head of the stream and still lazily operate on the rest. It
> is an ability that Java streams lack. So perhaps the way to go is to
> create a sort of LazyLinkedList in Java (if there isn't one.)
>
> -- Sebastian
>
Me I wouldn't re-invent the wheel in this case. Implementing this type 
of laziness is not that straightforward.

And why not use interop between JVM languages? This way you leverage the 
strengths. I usually have Java as the main language, but for some 
functionality in some apps I use Scala. Maintainability goes up, for 
starters, as does reliability and speed of development.

It's all ultimately JVM bytecode.

AHS

-- 
When a true genius appears, you can know him by this sign:
that all the dunces are in a confederacy against him.
-- Jonathan Swift