[Haskell-cafe] Haskell-Cafe Digest, Vol 152, Issue 27

Julian Leviston julian at getcontented.com.au
Sat Apr 23 12:36:04 UTC 2016

There were quite a few responses to you so far, but no one seemed to mention that what you actually asked for are called anamorphisms. 

https://en.wikipedia.org/wiki/Anamorphism <https://en.wikipedia.org/wiki/Anamorphism>

They’re not a *class* per se (as in… they’re not a typeclass), but rather they’re a kind of higher-order function which we call unfold (the kind-of “opposite" action to a fold).

Here’s a nice little thing I found which is quite helpful as an explanation:

and Data.List has unfoldr: http://hackage.haskell.org/package/base- <http://hackage.haskell.org/package/base->

If you google around for either "anamorphism Haskell” or “unfold Haskell” you’ll find some nice explanatory resources.

Hope that helps!

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> On 23 Apr 2016, at 10:00 PM, haskell-cafe-request at haskell.org wrote:
> Hi. I'm more in the shallow end of the Haskell pool right now, so
> forgive me if this is really basic... In Haskell, what is the class for
> things that can provide an infinite sequence? I mean, things that
> produce a value as well as function for producing the next value?
> Clearly RandomGen does this, but what is the next level of abstraction
> above RandomGen (i.e., RandomGen minus the randomness aspect).

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