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Today's Topics:
1. Re: Streams (mike h)
----------------------------------------------------------------------
Message: 1
Date: Thu, 27 Jul 2017 13:29:00 +0100
From: mike h <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Streams
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
Thanks Francesco - I’ll follow up the link.
M
> On 27 Jul 2017, at 11:08, Francesco Ariis <[email protected]> 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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