On Wed, Sep 24, 2008 at 03:59:12PM +0100, Simon Marlow wrote:
Claus Reinke wrote:
This raises the more general issue of instance-visibility. Since instances are automatically re-exported and therefore break abstraction barriers, the only sensible way to think about instances is as global properties.
I've heard this fatalistic view expressed before, and even for impoverished Haskell 98, it just isn't true. Perhaps it has come about from years of being bitten by either #2182, by attempts to avoid "orphan" instances, by carelessly designed libraries, or by careless instance imports, all of which make combining libraries that provide instances of the same class for the same type a pain?
No, it has nothing to do with bugs or misfeatures in GHC, it's a fact of Haskell 98.
Except for #2356, which some people think is a feature. (Not me, though)