Re: [Haskell-cafe] Safe Haskell and instance coherence

Hello, On Thu, Oct 11, 2012 at 3:54 PM, MigMit wrote:

You have a bigger problem coming. Some extensions make multiple instances OK, even in Safe Haskell. For example:

{-# LANGUAGE FlexibleInstances, IncoherentInstances, Safe #-} [...]

Safe Haskell already disallows OverlappingInstances. If we add a requirement that it must be unambiguous which instance declaration a given type class constraint resolves to (taking into account instances defined in all modules), I think it will be necessary to also disallow IncoherentInstances. -- () ascii ribbon campaign - against html e-mail /\ www.asciiribbon.org - against proprietary attachments