Re: [Haskell-cafe] Overlapping instances with "instance F a => G a"

1 Jan 2015


      On Thu, Jan 01, 2015 at 01:29:59PM -0800, Bryan Gardiner wrote:
...
Overlapping instances for HostBinary Word8
[..]
...
Doesn't "HostBinaryNum a => HostBinary a" create a HostBinary instance
for all instances of HostBinaryNum only?
[..]
  instance HostBinary Word8 where
[..]
  instance HostBinaryNum a => HostBinary a where
AIUI `instance HostBinaryNum a => HostBinary a` means "Every instance of the
form `HostBinary a` arises from an instance for `HostBinaryNum a`", so
provding an additional instance `HostBinary Word8` creates (potential)
overlap.

Tom

Re: [Haskell-cafe] Overlapping instances with "instance F a => G a"

Tom Ellis