marlowsd at gmail.com
Fri Sep 26 11:33:14 EDT 2008
Claus Reinke wrote:
>> .. I'm not trying to say that Haskell 98 only supports global
>> instances, rather I'm saying we should think of it that way and design
>> our libraries with global instances in mind, because otherwise we have
>> serious problems with abstraction.
> Thinking of it that way still doesn't make it so. If you want instances
> to be global, you have to change Haskell 98, by propagating instances
> through the whole program.
Sigh. I'm not having much luck convincing you, so let me try a
different tack. Here's a scenario I'd like your opinion on:
We have a test in GHC's test suite called instance-leak, which tests
that none of the Haskell 98 libraries exports the Functor instance for
(->). I broke this test recently by accident. How did I break it? By
using Data.Map internally in System.Process. The Functor instance for
(->) is exported from Control.Monad.Instances, makes its way into
Data.Map, then into System.Process and thereby into System, which is a
Haskell 98 module.
In your opinion, who or what is at fault for this test failure? Think
carefully about the ramifications of your answer. Oh, and "Haskell 98"
is not a valid answer, because we can't change that.
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