Changes between Version 18 and Version 19 of Proposals/transformers

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Timestamp:
11/05/10 09:45:01 (4 years ago)
Author:
ross (IP: 81.98.180.212)
Comment:

simpler suggestion for Functor constraint error

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  • Proposals/transformers

    v18 v19  
    107107 
    108108''Could not deduce (Functor m) from the context (Monad m)'' 
    109  This will be in a situation where you're using a monad constructed with a transformer as a Functor.  You can replace the {{{Monad m}} with {{{Functor m}}}.  Alternatively, if you add a {{{Functor m}}} constraint it will work with old and new versions of mtl. 
     109 This will be in a situation where you're using a monad constructed with a transformer as a Functor.  If this is triggered by a use of {{{fmap}}}, you can replace it with {{{liftM}}} and the code will build with old and new versions of mtl.  Alternatively, you can replace the {{{Monad m}}} with {{{Functor m}}} to make it work with mtl-2, or add a {{{Functor m}}} constraint to make it work with old and new versions of mtl. 
    110110 
    111111''Not in scope: data constructor State''