[Haskell] How to avoid both duplicate instances and extraneous instance declarations?

Robin Bate Boerop robin_bb at acm.org
Sat Apr 22 13:18:15 EDT 2006

The error given by GHC (with or without the -fallow-overlapping- 
instances) is

     Duplicate instance declarations:
       question.hs:6:0: instance (B1 x) => A x
       question.hs:7:0: instance (B2 x) => A x

Robin Bate Boerop

On 22-Apr-06, at 1:01 PM, ihope wrote:

> On 4/22/06, Robin Bate Boerop <robin_bb at acm.org> wrote:
>> This does not work.  The compiler gives the same error with or
>> without "-fallow-overlapping-instances".
> Just what is the error?

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