(:~:) is from Data.Type.Equality.
data a :~: b where
Refl :: a :~: a
On Jan 14, 2016 8:56 AM, "Andreas Abel"
What does this smiley :~: stand for?
On 13.01.2016 06:58, David Feuer wrote:
These are not likely to be *useful*, but they fall easily into the general bucket of "exactly one sensible instance exists".
instance Semigroup (a :~: b) where r <> _ = r
instance a ~ b => Monoid (a :~: b) where mempty = Refl mappend r _ = r _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
-- Andreas Abel <>< Du bist der geliebte Mensch.
Department of Computer Science and Engineering Chalmers and Gothenburg University, Sweden
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