[Haskell-cafe] instance of String illegal

[Bernie Pope]

On 29/09/2006, at 12:44 PM, Donald Bruce Stewart wrote:

>
> Alternatively, use -fglasgow-exts :)
>
>> instance Foo String where
>>     mkFoo = id
>
> $ ghci -fglasgow-exts A.hs
> *Main> mkFoo "foo"
> "foo"
>

And just to follow up what Don said, this feature of GHC is described  
here:

    http://www.haskell.org/ghc/docs/latest/html/users_guide/type- 
extensions.html