Re: [Haskell-cafe] manage effects in a DSL

On 10 Feb 2014, at 19:03, Brandon Allbery wrote:

On Mon, Feb 10, 2014 at 5:33 AM, Dominique Devriese 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.

You can easily achieve the same thing with orphan instances, and they only result in a compiler warning.