17 Jan
2016
17 Jan
'16
7:02 p.m.
+1, with a one stipulation: I'd rather the Semigroup instance be: instance Semigroup (a :~: b) where Refl <> Refl = Refl and similarly for Monoid(mappend). It's a minor quibble, but the documentation [1] for (:~:) says that there's only a proof term for a ~ b if it's inhabited by a terminating value, so performing a strict pattern match seems like the best default here. Ryan S. ----- [1] http://hackage.haskell.org/package/base-4.8.1.0/docs/Data-Type-Equality.html...: