[Haskell-cafe] Re: Arrow instance of Transducer (Was: [Haskell] ANN: Streaming Component Combinators 0.4)

Twan van Laarhoven twanvl at gmail.com
Sun Jan 17 16:47:48 EST 2010

Mario Blažević wrote:
>     After some investigation, I've concluded that Transducer cannot be made an
> instance of Arrow in any way that's both practical and general.
> the arr and (>>>) methods are trivial:
> but there is no satisfactory definition for the method first.

The Arrow class is too big, it includes too many things and it should be split 
up. This is yet another example. You can get some of the benefits of standard 
classes by making Transducer an instance of Control.Category.Category, for which 
you only need to implement (.) and id.


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