> On Tue Apr 18 10:31:30 UTC 2017, Simon Peyton Jones wrote:
>
> Moreover, as discussed in the user manual section,
> GHC doesnt complain about overlapping instances at the
instance decl,
> but rather where the instances are used.
Thank you Simon, yes I knew that, so I'd written a usage
(just did
verlap complaint
here
Simon
From: Glasgow-haskell-users [mailto:glasgow-haskell-users-boun...@haskell.org]
On Behalf Of Iavor Diatchki
Sent: 18 April 2017 01:50
To: anthony_clay...@clear.net.nz
Cc: GHC Users Mailing List
Subject: Re: Why isn't this Overlapping?
Hello,
these two instances reall
> On Tue Apr 18 00:50:20 UTC 2017, Iavor Diatchki wrote:
>
> these two instances really should be rejected as they
> violate the FD of the class: we can derive `TypeEq a a
> True` using the first instance and `TypeEq a a False`
> using the second one. Unfortunately, the check that we
> are using
Hello,
these two instances really should be rejected as they violate the FD of the
class: we can derive `TypeEq a a True` using the first instance and `TypeEq
a a False` using the second one. Unfortunately, the check that we are
using to validate FDs when `UndecidableInstances` is on, is not quit
--ghc 7.10 or 8.0.1
{-# LANGUAGE DataKinds, KindSignatures, GADTs,
MultiParamTypeClasses,
FunctionalDependencies, FlexibleInstances,
UndecidableInstances,
NoOverlappingInstances #-}
class TypeEq a a' (b :: Bool) | a a' -> b
instance (b ~ True
