23 Feb
2011
23 Feb
'11
10:18 a.m.
On Wed, 2011-02-23 at 08:42 -0600, Kurt Stutsman wrote:
When I was reviewing the Haskell language specification on haskell.org, it certainly looked like what I was doing was supported by the language. I found some comments on GHC's site about the reasoning behind these flags, but I couldn't tell if they were restrictions GHC had added to their implementation or if they derive from the language spec. Is this kind of instance allowed by the spec?
FlexibleInstances and UndecidableInstances are language extensions that relax the rules in the Haskell Report. If they are needed, then the instances you are writing are not allowed by the spec. -- Chris