On Mon, Feb 10, 2014 at 5:33 AM, Dominique Devriese <dominique.devriese@cs.kuleuven.be> wrote:
Local instances were already considered by Wadler when he proposed
type classes, but they are problematic to combine with type inference

Local instances have a bigger problem: you can use them to trivially violate invariants. Consider a local replacement for Ord on a Data.Map. They're not going to happen.

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