In your class Sum example,
class Sum x y z | x y - z, x z - y
your own solution has a bunch of helper classes
First of all, on the top of other issues, I haven't actually shown an
implementation in the message on Haskell'. I posed this as a general
issue.
In special cases like
On Tue, Apr 30, 2013 at 09:46:01PM -0400, Edward Kmett wrote:
instance Foldable Baz where
foldmap f (Baz a) = f a
is an innocent typo that would then just mean that foldMap when applied to
Baz will silently loop forever with no warning to the programmer.
Traversable Baz behaves similarly with
