Hello, Such a pragma sounds useful, and is very much like the "fails" instance from the "Instance chains" paper. You may also be interested in ticket #9334 (https://ghc.haskell.org/trac/ghc/ticket/9334), which proposes an alternative to overlapping instances, and I just updated it to point to #7775.
-Iavor On Sun, Aug 10, 2014 at 7:19 AM, Henning Thielemann < schlepp...@henning-thielemann.de> wrote: > Am 29.07.2014 um 12:02 schrieb Johan Tibell: > > P.S. For e.g. INLINABLE we require that you mention the function name >> next to the pragma (which means that you can e.g. put the pragma after >> the declaration). What's the rationale to not require >> >> {-# OVERLAPPING Show [Char] #-} >> >> here? Perhaps it's too annoying to have to repeat the types? >> > > Once I proposed a pragma for documenting intentionally unimplemented > instances. In this case there is no instance you can write a pragma in > front of. Your OVERLAPPING syntax would be conform with the one of > NOINSTANCE: > > https://ghc.haskell.org/trac/ghc/ticket/7775 > > Maybe NOINSTANCE can be reconsidered in the course of the introduction of > the OVERLAP pragma? > >
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