[Haskell-cafe] How to define instance for type synonym with parameter.

Brandon S. Allbery KF8NH allbery at ece.cmu.edu
Tue Mar 16 21:55:51 EDT 2010

On Mar 16, 2010, at 17:03 , Vasyl Pasternak wrote:
>> Aren't ErrorT and ReaderT instances of Applicative already? (At  
>> least in
>> 'transformers' package?)
> what difference between 'mtl' and 'transformers' packages ? 'mtl' goes
> with Haskell Platform as standard package, so what is the benefit of
> 'transformers' library ?

mtl is being deprecated (not just yet but soon); transformers is more  
general and provides the ability to support type families as well as  
functional dependencies (many folks believe type families are the  
future of Haskell, because functional dependencies are often difficult  
to understand).

brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery at kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery at ece.cmu.edu
electrical and computer engineering, carnegie mellon university    KF8NH

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