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Re: [Haskell-cafe] Re: Arrow instance of Transducer (Was: [Haskell] ANN:

Subject: Re: [Haskell-cafe] Re: Arrow instance of Transducer Was: [Haskell] ANN: Streaming Component Combinators 0.4
From: Twan van Laarhoven
Date: Sun, 17 Jan 2010 22:47:48 +0100
Mario BlaÅeviÄ 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.

Twan
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