[Haskell-beginners] Streams

[mike h]

Thanks Francesco - I’ll follow up the link.
M
> On 27 Jul 2017, at 11:08, Francesco Ariis <fa-ml at ariis.it> wrote:
> 
> On Thu, Jul 27, 2017 at 09:33:33AM +0100, mike h wrote:
>> What I'd like to do is take one item at a time from the stream. My first
>> shot was 
>> 
>> next :: (Stream a) -> (Stream a, a)
>> 
>> but that means I need to keep a ref to the stream that is returned in the tuple which makes for messy code
>> for subsequent calls to next. I sense that the State monad needs to be involved but I'm not sure exactly how as 
>> my experiments with State still required I keep a ref to the 'new' stream. Conceptually I see this as a 'global' state
>> and  next is just
>> 
>> next :: a
>> 
>> but that's 30 years of imperative programming speaking and is, I think,
>> wrong! 
> 
> Hello Mike,
> 
>    I see nothing wrong with a State monad (you signature looks really like
> the one inside a State monad, after all)
> 
>    next  :: Stream a -> (a, Stream a)
>    next' :: s        -> (a, s       )
> 
> Many many many other ways of dealing elegantly with streams have been
> proposed; check for example this article [1], which starts exactly
> from your example, e.g.
> 
>    data Stream b = SCons (b, Stream b)
> 
> And then, if you are sold to the idea, exploring the various libraries
> on hackage is the other half of the fun :P
> -F
> 
> [1] https://blog.jle.im/entry/intro-to-machines-arrows-part-1-stream-and
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