'deriving Tree (Eq,Ord)'

Simon Marlow simonmar at microsoft.com
Tue Apr 4 11:44:48 EDT 2006

On 04 April 2006 14:35, Bulat Ziganshin wrote:

> Hello Ross,
> Tuesday, April 4, 2006, 4:55:09 PM, you wrote:
>>> http://www.cse.unsw.edu.au/~dons/haskell-1990-2000/msg00727.html
>> (Making 'deriving' a separate declaration instead of a clause)
>> Orphan instances are discouraged in the GHC libraries, so there might
>> not be much support for adding a feature designed to permit orphan
>> derived instances.
> sorry, i don't understand how them are discouraged? GHC can't support
> this because of it's internal limits? i think you mean some other
> thing but i can't understand you

Discouraged in the sense of "it works fine, but we don't recommend it".
Compilation times may be worse if you have orphan instances, because the
compiler *always* has to read an interface file containing an orphan
instance if it is in the transitive closure of imported modules.


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