[Haskell-cafe] Stream fusion and span/break/group/init/tails

[Gábor Lehel]

On Mon, Apr 29, 2013 at 8:35 PM, Duncan Coutts <duncan.coutts at googlemail.com
> wrote:

> On Mon, 2013-04-29 at 20:19 +0200, Gábor Lehel wrote:
>
> > Thanks for the explanation. I looked at your thesis previously, but only
> > read through a couple of sections (including the one about concatMap). I
> > might go through the state machine parts as well now that I know the
> > significance/relevance.
> >
> > The thing in particular that was motivating me is that if it weren't for
> > Skip, it seems that to some extent (I haven't had time to investigate
> > precisely what extent) you could write a stream fusion framework in a
> > datatype-generic way, parameterized over the base functor. But it wasn't
> > obvious to me how (or whether) you would translate Skip. But maybe the
> > state machine perspective will provide some insight into that. I'll think
> > about it.
>
> Oh I think you can write it in a data-type generic way.
>
> If your datatype is described by a base functor F, then the skip version
> is a simple transformation on that functor.
>
> F_skip a = F a + a
>
> And then the stream type for F is  nu a. F_skip a
>
> See section 3.6.
>
> In most of my theory chapter I write it in this style, rather than using
> the list functor specifically.
>
> Duncan
>
>
Oh. So basically it does just amount to adding a `Skip s` constructor to
whatever the base functor was. I definitely should read more of it. Thanks
again!

-- 
Your ship was destroyed in a monadic eruption.
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