[Haskell-cafe] Problem on overlapping instances

Jasper Van der Jeugt jaspervdj at gmail.com
Wed Jan 5 09:33:05 CET 2011


    {-# LANGUAGE OverlappingInstances, FlexibleInstances #-}
    import Data.Binary

    instance Binary [String] where
        get = undefined
        put = undefined

works fine here on GHC 6.12.3. That being said, it would be safer
perhaps to add a newtype around [String] so you can avoid the orphan
instance as well, i.e.

    import Data.Binary

    newtype MyType = MyType [String]

    instance Binary MyType where
        get = undefined
        put = undefined


On Wed, Jan 5, 2011 at 9:24 AM, Magicloud Magiclouds
<magicloud.magiclouds at gmail.com> wrote:
> Hi,
>  I am using Data.Binary which defined "instance Binary a => Binary
> [a]". Now I need to define "instance Binary [String]" to make
> something special for string list.
>  How to make it work? I looked into the chapter of
> overlappinginstances, nothing works.
> --
> 竹密岂妨流水过
> 山高哪阻野云飞
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe at haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe

More information about the Haskell-Cafe mailing list